FFmpeg源代码分析：libswswcale的sws_getContext()
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打算写两篇文章记录FFmpeg中的图像处理（缩放，YUV/RGB格式转换）类库libswsscale的源代码。libswscale是一个主要用于处理图片像素数据的类库。可以完成图片像素格式的转换，图片的拉伸等工作。有关libswscale的使用可以参考文章：
《最简单的基于FFmpeg的libswscale的示例（YUV转RGB）》
libswscale常用的函数数量很少，一般情况下就3个：
sws_getContext()：初始化一个SwsContext。
sws_scale()：处理图像数据。
sws_freeContext()：释放一个SwsContext。其中sws_getContext()也可以用sws_getCachedContext()取代。
尽管libswscale从表面上看常用函数的个数不多，它的内部却有一个大大的“世界”。做为一个几乎“万能”的图片像素数据处理类库，它的内部包含了大量的代码。因此计划写两篇文章分析它的源代码。本文首先分析它的初始化函数sws_getContext()，而下一篇文章则分析它的数据处理函数sws_scale()。
函数调用结构图
分析得到的libswscale的函数调用关系如下图所示。
Libswscale处理数据流程
Libswscale处理像素数据的流程可以概括为下图。
从图中可以看出，libswscale处理数据有两条最主要的方式：unscaled和scaled。unscaled用于处理不需要拉伸的像素数据（属于比较特殊的情况），scaled用于处理需要拉伸的像素数据。Unscaled只需要对图像像素格式进行转换；而Scaled则除了对像素格式进行转换之外，还需要对图像进行缩放。Scaled方式可以分成以下几个步骤：
SwsContext
SwsContext是使用libswscale时候一个贯穿始终的结构体。但是我们在使用FFmpeg的类库进行开发的时候，是无法看到它的内部结构的。在libswscale\swscale.h中只能看到一行定义：struct SwsContext;一般人看到这个只有一行定义的结构体，会猜测它的内部一定十分简单。但是假使我们看一下FFmpeg的源代码，会发现这个猜测是完全错误的??SwsContext的定义是十分复杂的。它的定义位于libswscale\swscale_internal.h中，如下所示。
/* This struct should be aligned on at least a 32-byte boundary. */typedef struct SwsContext { /** * info on struct for av_log */ const AVClass *av_class; /** * Note that src, dst, srcStride, dstStride will be copied in the * sws_scale() wrapper so they can be freely modified here. */ SwsFunc swscale; int srcW; ///< Width of source luma/alpha planes. int srcH; ///< Height of source luma/alpha planes. int dstH; ///< Height of destination luma/alpha planes. int chrSrcW; ///< Width of source chroma planes. int chrSrcH; ///< Height of source chroma planes. int chrDstW; ///< Width of destination chroma planes. int chrDstH; ///< Height of destination chroma planes. int lumXInc, chrXInc; int lumYInc, chrYInc; enum AVPixelFormat dstFormat; ///< Destination pixel format. enum AVPixelFormat srcFormat; ///< Source pixel format. int dstFormatBpp; ///< Number of bits per pixel of the destination pixel format. int srcFormatBpp; ///< Number of bits per pixel of the source pixel format. int dstBpc, srcBpc; int chrSrcHSubSample; ///< Binary logarithm of horizontal subsampling factor between luma/alpha and chroma planes in source image. int chrSrcVSubSample; ///< Binary logarithm of vertical subsampling factor between luma/alpha and chroma planes in source image. int chrDstHSubSample; ///< Binary logarithm of horizontal subsampling factor between luma/alpha and chroma planes in destination image. int chrDstVSubSample; ///< Binary logarithm of vertical subsampling factor between luma/alpha and chroma planes in destination image. int vChrDrop; ///< Binary logarithm of extra vertical subsampling factor in source image chroma planes specified by user. int sliceDir; ///< Direction that slices are fed to the scaler (1 = top-to-bottom, -1 = bottom-to-top). double param[2]; ///< Input parameters for scaling algorithms that need them. /* The cascaded_* fields allow spliting a scaler task into multiple * sequential steps, this is for example used to limit the maximum * downscaling factor that needs to be supported in one scaler. */ struct SwsContext *cascaded_context[2]; int cascaded_tmpStride[4]; uint8_t *cascaded_tmp[4]; uint32_t pal_yuv[256]; uint32_t pal_rgb[256]; /** * @name Scaled horizontal lines ring buffer. * The horizontal scaler keeps just enough scaled lines in a ring buffer * so they may be passed to the vertical scaler. The pointers to the * allocated buffers for each line are duplicated in sequence in the ring * buffer to simplify indexing and avoid wrapping around between lines * inside the vertical scaler code. The wrapping is done before the * vertical scaler is called. */ //@{ int16_t **lumPixBuf; ///< Ring buffer for scaled horizontal luma plane lines to be fed to the vertical scaler. int16_t **chrUPixBuf; ///< Ring buffer for scaled horizontal chroma plane lines to be fed to the vertical scaler. int16_t **chrVPixBuf; ///< Ring buffer for scaled horizontal chroma plane lines to be fed to the vertical scaler. int16_t **alpPixBuf; ///< Ring buffer for scaled horizontal alpha plane lines to be fed to the vertical scaler. int vLumBufSize; ///< Number of vertical luma/alpha lines allocated in the ring buffer. int vChrBufSize; ///< Number of vertical chroma lines allocated in the ring buffer. int lastInLumBuf; ///< Last scaled horizontal luma/alpha line from source in the ring buffer. int lastInChrBuf; ///< Last scaled horizontal chroma line from source in the ring buffer. int lumBufIndex; ///< Index in ring buffer of the last scaled horizontal luma/alpha line from source. int chrBufIndex; ///< Index in ring buffer of the last scaled horizontal chroma line from source. //@} uint8_t *formatConvBuffer; /** * @name Horizontal and vertical filters. * To better understand the following fields, here is a pseudo-code of * their usage in filtering a horizontal line: * @code * for (i = 0; i < width; i++) { * dst[i] = 0; * for (j = 0; j < filterSize; j++) * dst[i] += src[ filterPos[i] + j ] * filter[ filterSize * i + j ]; * dst[i] >>= FRAC_BITS; // The actual implementation is fixed-point. * } * @endcode */ //@{ int16_t *hLumFilter; ///< Array of horizontal filter coefficients for luma/alpha planes. int16_t *hChrFilter; ///< Array of horizontal filter coefficients for chroma planes. int16_t *vLumFilter; ///< Array of vertical filter coefficients for luma/alpha planes. int16_t *vChrFilter; ///< Array of vertical filter coefficients for chroma planes. int32_t *hLumFilterPos; ///< Array of horizontal filter starting positions for each dst[i] for luma/alpha planes. int32_t *hChrFilterPos; ///< Array of horizontal filter starting positions for each dst[i] for chroma planes. int32_t *vLumFilterPos; ///< Array of vertical filter starting positions for each dst[i] for luma/alpha planes. int32_t *vChrFilterPos; ///< Array of vertical filter starting positions for each dst[i] for chroma planes. int hLumFilterSize; ///< Horizontal filter size for luma/alpha pixels. int hChrFilterSize; ///< Horizontal filter size for chroma pixels. int vLumFilterSize; ///< Vertical filter size for luma/alpha pixels. int vChrFilterSize; ///< Vertical filter size for chroma pixels. //@} int lumMmxextFilterCodeSize; ///< Runtime-generated MMXEXT horizontal fast bilinear scaler code size for luma/alpha planes. int chrMmxextFilterCodeSize; ///< Runtime-generated MMXEXT horizontal fast bilinear scaler code size for chroma planes. uint8_t *lumMmxextFilterCode; ///< Runtime-generated MMXEXT horizontal fast bilinear scaler code for luma/alpha planes. uint8_t *chrMmxextFilterCode; ///< Runtime-generated MMXEXT horizontal fast bilinear scaler code for chroma planes. int canMMXEXTBeUsed; int dstY; ///< Last destination vertical line output from last slice. int flags; ///< Flags passed by the user to select scaler algorithm, optimizations, subsampling, etc... void *yuvTable; // pointer to the yuv->rgb table start so it can be freed() // alignment ensures the offset can be added in a single // instruction on e.g. ARM DECLARE_ALIGNED(16, int, table_gV)[256 + 2*YUVRGB_TABLE_HEADROOM]; uint8_t *table_rV[256 + 2*YUVRGB_TABLE_HEADROOM]; uint8_t *table_gU[256 + 2*YUVRGB_TABLE_HEADROOM]; uint8_t *table_bU[256 + 2*YUVRGB_TABLE_HEADROOM]; DECLARE_ALIGNED(16, int32_t, input_rgb2yuv_table)[16+40*4]; // This table can contain both C and SIMD formatted values, the C vales are always at the XY_IDX points#define RY_IDX 0#define GY_IDX 1#define BY_IDX 2#define RU_IDX 3#define GU_IDX 4#define BU_IDX 5#define RV_IDX 6#define GV_IDX 7#define BV_IDX 8#define RGB2YUV_SHIFT 15 int *dither_error[4]; //Colorspace stuff int contrast, brightness, saturation; // for sws_getColorspaceDetails int srcColorspaceTable[4]; int dstColorspaceTable[4]; int srcRange; ///< 0 = MPG YUV range, 1 = JPG YUV range (source image). int dstRange; ///< 0 = MPG YUV range, 1 = JPG YUV range (destination image). int src0Alpha; int dst0Alpha; int srcXYZ; int dstXYZ; int src_h_chr_pos; int dst_h_chr_pos; int src_v_chr_pos; int dst_v_chr_pos; int yuv2rgb_y_offset; int yuv2rgb_y_coeff; int yuv2rgb_v2r_coeff; int yuv2rgb_v2g_coeff; int yuv2rgb_u2g_coeff; int yuv2rgb_u2b_coeff;#define RED_DITHER "0*8"#define GREEN_DITHER "1*8"#define BLUE_DITHER "2*8"#define Y_COEFF "3*8"#define VR_COEFF "4*8"#define UB_COEFF "5*8"#define VG_COEFF "6*8"#define UG_COEFF "7*8"#define Y_OFFSET "8*8"#define U_OFFSET "9*8"#define V_OFFSET "10*8"#define LUM_MMX_FILTER_OFFSET "11*8"#define CHR_MMX_FILTER_OFFSET "11*8+4*4*"AV_STRINGIFY(MAX_FILTER_SIZE)#define DSTW_OFFSET "11*8+4*4*"AV_STRINGIFY(MAX_FILTER_SIZE)"*2"#define ESP_OFFSET "11*8+4*4*"AV_STRINGIFY(MAX_FILTER_SIZE)"*2+8"#define VROUNDER_OFFSET "11*8+4*4*"AV_STRINGIFY(MAX_FILTER_SIZE)"*2+16"#define U_TEMP "11*8+4*4*"AV_STRINGIFY(MAX_FILTER_SIZE)"*2+24"#define V_TEMP "11*8+4*4*"AV_STRINGIFY(MAX_FILTER_SIZE)"*2+32"#define Y_TEMP "11*8+4*4*"AV_STRINGIFY(MAX_FILTER_SIZE)"*2+40"#define ALP_MMX_FILTER_OFFSET "11*8+4*4*"AV_STRINGIFY(MAX_FILTER_SIZE)"*2+48"#define UV_OFF_PX "11*8+4*4*"AV_STRINGIFY(MAX_FILTER_SIZE)"*3+48"#define UV_OFF_BYTE "11*8+4*4*"AV_STRINGIFY(MAX_FILTER_SIZE)"*3+56"#define DITHER16 "11*8+4*4*"AV_STRINGIFY(MAX_FILTER_SIZE)"*3+64"#define DITHER32 "11*8+4*4*"AV_STRINGIFY(MAX_FILTER_SIZE)"*3+80"#define DITHER32_INT (11*8+4*4*MAX_FILTER_SIZE*3+80) // value equal to above, used for checking that the struct hasn't been changed by mistake DECLARE_ALIGNED(8, uint64_t, redDither); DECLARE_ALIGNED(8, uint64_t, greenDither); DECLARE_ALIGNED(8, uint64_t, blueDither); DECLARE_ALIGNED(8, uint64_t, yCoeff); DECLARE_ALIGNED(8, uint64_t, vrCoeff); DECLARE_ALIGNED(8, uint64_t, ubCoeff); DECLARE_ALIGNED(8, uint64_t, vgCoeff); DECLARE_ALIGNED(8, uint64_t, ugCoeff); DECLARE_ALIGNED(8, uint64_t, yOffset); DECLARE_ALIGNED(8, uint64_t, uOffset); DECLARE_ALIGNED(8, uint64_t, vOffset); int32_t lumMmxFilter[4 * MAX_FILTER_SIZE]; int32_t chrMmxFilter[4 * MAX_FILTER_SIZE]; int dstW; ///< Width of destination luma/alpha planes. DECLARE_ALIGNED(8, uint64_t, esp); DECLARE_ALIGNED(8, uint64_t, vRounder); DECLARE_ALIGNED(8, uint64_t, u_temp); DECLARE_ALIGNED(8, uint64_t, v_temp); DECLARE_ALIGNED(8, uint64_t, y_temp); int32_t alpMmxFilter[4 * MAX_FILTER_SIZE]; // alignment of these values is not necessary, but merely here // to maintain the same offset across x8632 and x86-64. Once we // use proper offset macros in the asm, they can be removed. DECLARE_ALIGNED(8, ptrdiff_t, uv_off); ///< offset (in pixels) between u and v planes DECLARE_ALIGNED(8, ptrdiff_t, uv_offx2); ///< offset (in bytes) between u and v planes DECLARE_ALIGNED(8, uint16_t, dither16)[8]; DECLARE_ALIGNED(8, uint32_t, dither32)[8]; const uint8_t *chrDither8, *lumDither8;#if HAVE_ALTIVEC vector signed short CY; vector signed short CRV; vector signed short CBU; vector signed short CGU; vector signed short CGV; vector signed short OY; vector unsigned short CSHIFT; vector signed short *vYCoeffsBank, *vCCoeffsBank;#endif int use_mmx_vfilter;/* pre defined color-spaces gamma */#define XYZ_GAMMA (2.6f)#define RGB_GAMMA (2.2f) int16_t *xyzgamma; int16_t *rgbgamma; int16_t *xyzgammainv; int16_t *rgbgammainv; int16_t xyz2rgb_matrix[3][4]; int16_t rgb2xyz_matrix[3][4]; /* function pointers for swscale() */ yuv2planar1_fn yuv2plane1; yuv2planarX_fn yuv2planeX; yuv2interleavedX_fn yuv2nv12cX; yuv2packed1_fn yuv2packed1; yuv2packed2_fn yuv2packed2; yuv2packedX_fn yuv2packedX; yuv2anyX_fn yuv2anyX; /// Unscaled conversion of luma plane to YV12 for horizontal scaler. void (*lumToYV12)(uint8_t *dst, const uint8_t *src, const uint8_t *src2, const uint8_t *src3, int width, uint32_t *pal); /// Unscaled conversion of alpha plane to YV12 for horizontal scaler. void (*alpToYV12)(uint8_t *dst, const uint8_t *src, const uint8_t *src2, const uint8_t *src3, int width, uint32_t *pal); /// Unscaled conversion of chroma planes to YV12 for horizontal scaler. void (*chrToYV12)(uint8_t *dstU, uint8_t *dstV, const uint8_t *src1, const uint8_t *src2, const uint8_t *src3, int width, uint32_t *pal); /** * Functions to read planar input, such as planar RGB, and convert * internally to Y/UV/A. */ /** @{ */ void (*readLumPlanar)(uint8_t *dst, const uint8_t *src[4], int width, int32_t *rgb2yuv); void (*readChrPlanar)(uint8_t *dstU, uint8_t *dstV, const uint8_t *src[4], int width, int32_t *rgb2yuv); void (*readAlpPlanar)(uint8_t *dst, const uint8_t *src[4], int width, int32_t *rgb2yuv); /** @} */ /** * Scale one horizontal line of input data using a bilinear filter * to produce one line of output data. Compared to SwsContext->hScale(), * please take note of the following caveats when using these: * - Scaling is done using only 7bit instead of 14bit coefficients. * - You can use no more than 5 input pixels to produce 4 output * pixels. Therefore, this filter should not be used for downscaling * by more than ~20% in width (because that equals more than 5/4th * downscaling and thus more than 5 pixels input per 4 pixels output). * - In general, bilinear filters create artifacts during downscaling * (even when <20%), because one output pixel will span more than one * input pixel, and thus some pixels will need edges of both neighbor * pixels to interpolate the output pixel. Since you can use at most * two input pixels per output pixel in bilinear scaling, this is * impossible and thus downscaling by any size will create artifacts. * To enable this type of scaling, set SWS_FLAG_FAST_BILINEAR * in SwsContext->flags. */ /** @{ */ void (*hyscale_fast)(struct SwsContext *c, int16_t *dst, int dstWidth, const uint8_t *src, int srcW, int xInc); void (*hcscale_fast)(struct SwsContext *c, int16_t *dst1, int16_t *dst2, int dstWidth, const uint8_t *src1, const uint8_t *src2, int srcW, int xInc); /** @} */ /** * Scale one horizontal line of input data using a filter over the input * lines, to produce one (differently sized) line of output data. * * @param dst pointer to destination buffer for horizontally scaled * data. If the number of bits per component of one * destination pixel (SwsContext->dstBpc) is <= 10, data * will be 15bpc in 16bits (int16_t) width. Else (i.e. * SwsContext->dstBpc == 16), data will be 19bpc in * 32bits (int32_t) width. * @param dstW width of destination image * @param src pointer to source data to be scaled. If the number of * bits per component of a source pixel (SwsContext->srcBpc) * is 8, this is 8bpc in 8bits (uint8_t) width. Else * (i.e. SwsContext->dstBpc > 8), this is native depth * in 16bits (uint16_t) width. In other words, for 9-bit * YUV input, this is 9bpc, for 10-bit YUV input, this is * 10bpc, and for 16-bit RGB or YUV, this is 16bpc. * @param filter filter coefficients to be used per output pixel for * scaling. This contains 14bpp filtering coefficients. * Guaranteed to contain dstW * filterSize entries. * @param filterPos position of the first input pixel to be used for * each output pixel during scaling. Guaranteed to * contain dstW entries. * @param filterSize the number of input coefficients to be used (and * thus the number of input pixels to be used) for * creating a single output pixel. Is aligned to 4 * (and input coefficients thus padded with zeroes) * to simplify creating SIMD code. */ /** @{ */ void (*hyScale)(struct SwsContext *c, int16_t *dst, int dstW, const uint8_t *src, const int16_t *filter, const int32_t *filterPos, int filterSize); void (*hcScale)(struct SwsContext *c, int16_t *dst, int dstW, const uint8_t *src, const int16_t *filter, const int32_t *filterPos, int filterSize); /** @} */ /// Color range conversion function for luma plane if needed. void (*lumConvertRange)(int16_t *dst, int width); /// Color range conversion function for chroma planes if needed. void (*chrConvertRange)(int16_t *dst1, int16_t *dst2, int width); int needs_hcscale; ///< Set if there are chroma planes to be converted. SwsDither dither;} SwsContext;这个结构体的定义确实比较复杂，里面包含了libswscale所需要的全部变量。一一分析这些变量是不太现实的，在后文中会简单分析其中的几个变量。
sws_getContext()
sws_getContext()是初始化SwsContext的函数。sws_getContext()的声明位于libswscale\swscale.h，如下所示。/** * Allocate and return an SwsContext. You need it to perform * scaling/conversion operations using sws_scale(). * * @param srcW the width of the source image * @param srcH the height of the source image * @param srcFormat the source image format * @param dstW the width of the destination image * @param dstH the height of the destination image * @param dstFormat the destination image format * @param flags specify which algorithm and options to use for rescaling * @return a pointer to an allocated context, or NULL in case of error * @note this function is to be removed after a saner alternative is * written */struct SwsContext *sws_getContext(int srcW, int srcH, enum AVPixelFormat srcFormat, int dstW, int dstH, enum AVPixelFormat dstFormat, int flags, SwsFilter *srcFilter, SwsFilter *dstFilter, const double *param);
该函数包含以下参数：
srcW：源图像的宽
srcH：源图像的高
srcFormat：源图像的像素格式
dstW：目标图像的宽
dstH：目标图像的高
dstFormat：目标图像的像素格式
flags：设定图像拉伸使用的算法 成功执行的话返回生成的SwsContext，否则返回NULL。
sws_getContext()的定义位于libswscale\utils.c，如下所示。
SwsContext *sws_getContext(int srcW, int srcH, enum AVPixelFormat srcFormat, int dstW, int dstH, enum AVPixelFormat dstFormat, int flags, SwsFilter *srcFilter, SwsFilter *dstFilter, const double *param){ SwsContext *c; if (!(c = sws_alloc_context())) return NULL; c->flags = flags; c->srcW = srcW; c->srcH = srcH; c->dstW = dstW; c->dstH = dstH; c->srcFormat = srcFormat; c->dstFormat = dstFormat; if (param) { c->param[0] = param[0]; c->param[1] = param[1]; } if (sws_init_context(c, srcFilter, dstFilter) < 0) { sws_freeContext(c); return NULL; } return c;}从sws_getContext()的定义中可以看出，它首先调用了一个函数sws_alloc_context()用于给SwsContext分配内存。然后将传入的源图像，目标图像的宽高，像素格式，以及标志位分别赋值给该SwsContext相应的字段。最后调用一个函数sws_init_context()完成初始化工作。下面我们分别看一下sws_alloc_context()和sws_init_context()这两个函数。
sws_alloc_context()
sws_alloc_context()是FFmpeg的一个API，用于给SwsContext分配内存，它的声明如下所示。/** * Allocate an empty SwsContext. This must be filled and passed to * sws_init_context(). For filling see AVOptions, options.c and * sws_setColorspaceDetails(). */struct SwsContext *sws_alloc_context(void);
sws_alloc_context()的定义位于libswscale\utils.c，如下所示。
SwsContext *sws_alloc_context(void){ SwsContext *c = av_mallocz(sizeof(SwsContext)); av_assert0(offsetof(SwsContext, redDither) + DITHER32_INT == offsetof(SwsContext, dither32)); if (c) { c->av_class = &sws_context_class; av_opt_set_defaults(c); } return c;}从代码中可以看出，sws_alloc_context()首先调用av_mallocz()为SwsContext结构体分配了一块内存；然后设置了该结构体的AVClass，并且给该结构体的字段设置了默认值。
sws_init_context()
sws_init_context()的是FFmpeg的一个API，用于初始化SwsContext。/** * Initialize the swscaler context sws_context. * * @return zero or positive value on success, a negative value on * error */int sws_init_context(struct SwsContext *sws_context, SwsFilter *srcFilter, SwsFilter *dstFilter);
sws_init_context()的函数定义非常的长，位于libswscale\utils.c，如下所示。
av_cold int sws_init_context(SwsContext *c, SwsFilter *srcFilter, SwsFilter *dstFilter){ int i, j; int usesVFilter, usesHFilter; int unscaled; SwsFilter dummyFilter = { NULL, NULL, NULL, NULL }; int srcW = c->srcW; int srcH = c->srcH; int dstW = c->dstW; int dstH = c->dstH; int dst_stride = FFALIGN(dstW * sizeof(int16_t) + 66, 16); int flags, cpu_flags; enum AVPixelFormat srcFormat = c->srcFormat; enum AVPixelFormat dstFormat = c->dstFormat; const AVPixFmtDescriptor *desc_src; const AVPixFmtDescriptor *desc_dst; int ret = 0; //获取 cpu_flags = av_get_cpu_flags(); flags = c->flags; emms_c(); if (!rgb15to16) sws_rgb2rgb_init(); //如果输入的宽高和输出的宽高一样，则做特殊处理 unscaled = (srcW == dstW && srcH == dstH); //如果是JPEG标准（Y取值0-255），则需要设置这两项 c->srcRange |= handle_jpeg(&c->srcFormat); c->dstRange |= handle_jpeg(&c->dstFormat); if(srcFormat!=c->srcFormat || dstFormat!=c->dstFormat) av_log(c, AV_LOG_WARNING, "deprecated pixel format used, make sure you did set range correctly\n"); //设置Colorspace if (!c->contrast && !c->saturation && !c->dstFormatBpp) sws_setColorspaceDetails(c, ff_yuv2rgb_coeffs[SWS_CS_DEFAULT], c->srcRange, ff_yuv2rgb_coeffs[SWS_CS_DEFAULT], c->dstRange, 0, 1 << 16, 1 << 16); handle_formats(c); srcFormat = c->srcFormat; dstFormat = c->dstFormat; desc_src = av_pix_fmt_desc_get(srcFormat); desc_dst = av_pix_fmt_desc_get(dstFormat); //转换大小端？ if (!(unscaled && sws_isSupportedEndiannessConversion(srcFormat) && av_pix_fmt_swap_endianness(srcFormat) == dstFormat)) { //检查输入格式是否支持 if (!sws_isSupportedInput(srcFormat)) { av_log(c, AV_LOG_ERROR, "%s is not supported as input pixel format\n", av_get_pix_fmt_name(srcFormat)); return AVERROR(EINVAL); } //检查输出格式是否支持 if (!sws_isSupportedOutput(dstFormat)) { av_log(c, AV_LOG_ERROR, "%s is not supported as output pixel format\n", av_get_pix_fmt_name(dstFormat)); return AVERROR(EINVAL); } } //检查拉伸的方法 i = flags & (SWS_POINT | SWS_AREA | SWS_BILINEAR | SWS_FAST_BILINEAR | SWS_BICUBIC | SWS_X | SWS_GAUSS | SWS_LANCZOS | SWS_SINC | SWS_SPLINE | SWS_BICUBLIN); /* provide a default scaler if not set by caller */ //如果没有指定，就使用默认的 if (!i) { if (dstW < srcW && dstH < srcH) flags |= SWS_BICUBIC; else if (dstW > srcW && dstH > srcH) flags |= SWS_BICUBIC; else flags |= SWS_BICUBIC; c->flags = flags; } else if (i & (i - 1)) { av_log(c, AV_LOG_ERROR, "Exactly one scaler algorithm must be chosen, got %X\n", i); return AVERROR(EINVAL); } /* sanity check */ //检查宽高参数 if (srcW < 1 || srcH < 1 || dstW < 1 || dstH < 1) { /* FIXME check if these are enough and try to lower them after * fixing the relevant parts of the code */ av_log(c, AV_LOG_ERROR, "%dx%d -> %dx%d is invalid scaling dimension\n", srcW, srcH, dstW, dstH); return AVERROR(EINVAL); } if (!dstFilter) dstFilter = &dummyFilter; if (!srcFilter) srcFilter = &dummyFilter; c->lumXInc = (((int64_t)srcW << 16) + (dstW >> 1)) / dstW; c->lumYInc = (((int64_t)srcH << 16) + (dstH >> 1)) / dstH; c->dstFormatBpp = av_get_bits_per_pixel(desc_dst); c->srcFormatBpp = av_get_bits_per_pixel(desc_src); c->vRounder = 4 * 0x0001000100010001ULL; usesVFilter = (srcFilter->lumV && srcFilter->lumV->length > 1) || (srcFilter->chrV && srcFilter->chrV->length > 1) || (dstFilter->lumV && dstFilter->lumV->length > 1) || (dstFilter->chrV && dstFilter->chrV->length > 1); usesHFilter = (srcFilter->lumH && srcFilter->lumH->length > 1) || (srcFilter->chrH && srcFilter->chrH->length > 1) || (dstFilter->lumH && dstFilter->lumH->length > 1) || (dstFilter->chrH && dstFilter->chrH->length > 1); av_pix_fmt_get_chroma_sub_sample(srcFormat, &c->chrSrcHSubSample, &c->chrSrcVSubSample); av_pix_fmt_get_chroma_sub_sample(dstFormat, &c->chrDstHSubSample, &c->chrDstVSubSample); if (isAnyRGB(dstFormat) && !(flags&SWS_FULL_CHR_H_INT)) { if (dstW&1) { av_log(c, AV_LOG_DEBUG, "Forcing full internal H chroma due to odd output size\n"); flags |= SWS_FULL_CHR_H_INT; c->flags = flags; } if ( c->chrSrcHSubSample == 0 && c->chrSrcVSubSample == 0 && c->dither != SWS_DITHER_BAYER //SWS_FULL_CHR_H_INT is currently not supported with SWS_DITHER_BAYER && !(c->flags & SWS_FAST_BILINEAR) ) { av_log(c, AV_LOG_DEBUG, "Forcing full internal H chroma due to input having non subsampled chroma\n"); flags |= SWS_FULL_CHR_H_INT; c->flags = flags; } } if (c->dither == SWS_DITHER_AUTO) { if (flags & SWS_ERROR_DIFFUSION) c->dither = SWS_DITHER_ED; } if(dstFormat == AV_PIX_FMT_BGR4_BYTE || dstFormat == AV_PIX_FMT_RGB4_BYTE || dstFormat == AV_PIX_FMT_BGR8 || dstFormat == AV_PIX_FMT_RGB8) { if (c->dither == SWS_DITHER_AUTO) c->dither = (flags & SWS_FULL_CHR_H_INT) ? SWS_DITHER_ED : SWS_DITHER_BAYER; if (!(flags & SWS_FULL_CHR_H_INT)) { if (c->dither == SWS_DITHER_ED || c->dither == SWS_DITHER_A_DITHER || c->dither == SWS_DITHER_X_DITHER) { av_log(c, AV_LOG_DEBUG, "Desired dithering only supported in full chroma interpolation for destination format '%s'\n", av_get_pix_fmt_name(dstFormat)); flags |= SWS_FULL_CHR_H_INT; c->flags = flags; } } if (flags & SWS_FULL_CHR_H_INT) { if (c->dither == SWS_DITHER_BAYER) { av_log(c, AV_LOG_DEBUG, "Ordered dither is not supported in full chroma interpolation for destination format '%s'\n", av_get_pix_fmt_name(dstFormat)); c->dither = SWS_DITHER_ED; } } } if (isPlanarRGB(dstFormat)) { if (!(flags & SWS_FULL_CHR_H_INT)) { av_log(c, AV_LOG_DEBUG, "%s output is not supported with half chroma resolution, switching to full\n", av_get_pix_fmt_name(dstFormat)); flags |= SWS_FULL_CHR_H_INT; c->flags = flags; } } /* reuse chroma for 2 pixels RGB/BGR unless user wants full * chroma interpolation */ if (flags & SWS_FULL_CHR_H_INT && isAnyRGB(dstFormat) && !isPlanarRGB(dstFormat) && dstFormat != AV_PIX_FMT_RGBA && dstFormat != AV_PIX_FMT_ARGB && dstFormat != AV_PIX_FMT_BGRA && dstFormat != AV_PIX_FMT_ABGR && dstFormat != AV_PIX_FMT_RGB24 && dstFormat != AV_PIX_FMT_BGR24 && dstFormat != AV_PIX_FMT_BGR4_BYTE && dstFormat != AV_PIX_FMT_RGB4_BYTE && dstFormat != AV_PIX_FMT_BGR8 && dstFormat != AV_PIX_FMT_RGB8 ) { av_log(c, AV_LOG_WARNING, "full chroma interpolation for destination format '%s' not yet implemented\n", av_get_pix_fmt_name(dstFormat)); flags &= ~SWS_FULL_CHR_H_INT; c->flags = flags; } if (isAnyRGB(dstFormat) && !(flags & SWS_FULL_CHR_H_INT)) c->chrDstHSubSample = 1; // drop some chroma lines if the user wants it c->vChrDrop = (flags & SWS_SRC_V_CHR_DROP_MASK) >> SWS_SRC_V_CHR_DROP_SHIFT; c->chrSrcVSubSample += c->vChrDrop; /* drop every other pixel for chroma calculation unless user * wants full chroma */ if (isAnyRGB(srcFormat) && !(flags & SWS_FULL_CHR_H_INP) && srcFormat != AV_PIX_FMT_RGB8 && srcFormat != AV_PIX_FMT_BGR8 && srcFormat != AV_PIX_FMT_RGB4 && srcFormat != AV_PIX_FMT_BGR4 && srcFormat != AV_PIX_FMT_RGB4_BYTE && srcFormat != AV_PIX_FMT_BGR4_BYTE && srcFormat != AV_PIX_FMT_GBRP9BE && srcFormat != AV_PIX_FMT_GBRP9LE && srcFormat != AV_PIX_FMT_GBRP10BE && srcFormat != AV_PIX_FMT_GBRP10LE && srcFormat != AV_PIX_FMT_GBRP12BE && srcFormat != AV_PIX_FMT_GBRP12LE && srcFormat != AV_PIX_FMT_GBRP14BE && srcFormat != AV_PIX_FMT_GBRP14LE && srcFormat != AV_PIX_FMT_GBRP16BE && srcFormat != AV_PIX_FMT_GBRP16LE && ((dstW >> c->chrDstHSubSample) <= (srcW >> 1) || (flags & SWS_FAST_BILINEAR))) c->chrSrcHSubSample = 1; // Note the FF_CEIL_RSHIFT is so that we always round toward +inf. c->chrSrcW = FF_CEIL_RSHIFT(srcW, c->chrSrcHSubSample); c->chrSrcH = FF_CEIL_RSHIFT(srcH, c->chrSrcVSubSample); c->chrDstW = FF_CEIL_RSHIFT(dstW, c->chrDstHSubSample); c->chrDstH = FF_CEIL_RSHIFT(dstH, c->chrDstVSubSample); FF_ALLOC_OR_GOTO(c, c->formatConvBuffer, FFALIGN(srcW*2+78, 16) * 2, fail); c->srcBpc = 1 + desc_src->comp[0].depth_minus1; if (c->srcBpc < 8) c->srcBpc = 8; c->dstBpc = 1 + desc_dst->comp[0].depth_minus1; if (c->dstBpc < 8) c->dstBpc = 8; if (isAnyRGB(srcFormat) || srcFormat == AV_PIX_FMT_PAL8) c->srcBpc = 16; if (c->dstBpc == 16) dst_stride <<= 1; if (INLINE_MMXEXT(cpu_flags) && c->srcBpc == 8 && c->dstBpc <= 14) { c->canMMXEXTBeUsed = dstW >= srcW && (dstW & 31) == 0 && c->chrDstW >= c->chrSrcW && (srcW & 15) == 0; if (!c->canMMXEXTBeUsed && dstW >= srcW && c->chrDstW >= c->chrSrcW && (srcW & 15) == 0 && (flags & SWS_FAST_BILINEAR)) { if (flags & SWS_PRINT_INFO) av_log(c, AV_LOG_INFO, "output width is not a multiple of 32 -> no MMXEXT scaler\n"); } if (usesHFilter || isNBPS(c->srcFormat) || is16BPS(c->srcFormat) || isAnyRGB(c->srcFormat)) c->canMMXEXTBeUsed = 0; } else c->canMMXEXTBeUsed = 0; c->chrXInc = (((int64_t)c->chrSrcW << 16) + (c->chrDstW >> 1)) / c->chrDstW; c->chrYInc = (((int64_t)c->chrSrcH << 16) + (c->chrDstH >> 1)) / c->chrDstH; /* Match pixel 0 of the src to pixel 0 of dst and match pixel n-2 of src * to pixel n-2 of dst, but only for the FAST_BILINEAR mode otherwise do * correct scaling. * n-2 is the last chrominance sample available. * This is not perfect, but no one should notice the difference, the more * correct variant would be like the vertical one, but that would require * some special code for the first and last pixel */ if (flags & SWS_FAST_BILINEAR) { if (c->canMMXEXTBeUsed) { c->lumXInc += 20; c->chrXInc += 20; } // we don't use the x86 asm scaler if MMX is available else if (INLINE_MMX(cpu_flags) && c->dstBpc <= 14) { c->lumXInc = ((int64_t)(srcW - 2) << 16) / (dstW - 2) - 20; c->chrXInc = ((int64_t)(c->chrSrcW - 2) << 16) / (c->chrDstW - 2) - 20; } } if (isBayer(srcFormat)) { if (!unscaled || (dstFormat != AV_PIX_FMT_RGB24 && dstFormat != AV_PIX_FMT_YUV420P)) { enum AVPixelFormat tmpFormat = AV_PIX_FMT_RGB24; ret = av_image_alloc(c->cascaded_tmp, c->cascaded_tmpStride, srcW, srcH, tmpFormat, 64); if (ret < 0) return ret; c->cascaded_context[0] = sws_getContext(srcW, srcH, srcFormat, srcW, srcH, tmpFormat, flags, srcFilter, NULL, c->param); if (!c->cascaded_context[0]) return -1; c->cascaded_context[1] = sws_getContext(srcW, srcH, tmpFormat, dstW, dstH, dstFormat, flags, NULL, dstFilter, c->param); if (!c->cascaded_context[1]) return -1; return 0; } }#define USE_MMAP (HAVE_MMAP && HAVE_MPROTECT && defined MAP_ANONYMOUS) /* precalculate horizontal scaler filter coefficients */ {#if HAVE_MMXEXT_INLINE// can't downscale !!! if (c->canMMXEXTBeUsed && (flags & SWS_FAST_BILINEAR)) { c->lumMmxextFilterCodeSize = ff_init_hscaler_mmxext(dstW, c->lumXInc, NULL, NULL, NULL, 8); c->chrMmxextFilterCodeSize = ff_init_hscaler_mmxext(c->chrDstW, c->chrXInc, NULL, NULL, NULL, 4);#if USE_MMAP c->lumMmxextFilterCode = mmap(NULL, c->lumMmxextFilterCodeSize, PROT_READ | PROT_WRITE, MAP_PRIVATE | MAP_ANONYMOUS, -1, 0); c->chrMmxextFilterCode = mmap(NULL, c->chrMmxextFilterCodeSize, PROT_READ | PROT_WRITE, MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);#elif HAVE_VIRTUALALLOC c->lumMmxextFilterCode = VirtualAlloc(NULL, c->lumMmxextFilterCodeSize, MEM_COMMIT, PAGE_EXECUTE_READWRITE); c->chrMmxextFilterCode = VirtualAlloc(NULL, c->chrMmxextFilterCodeSize, MEM_COMMIT, PAGE_EXECUTE_READWRITE);#else c->lumMmxextFilterCode = av_malloc(c->lumMmxextFilterCodeSize); c->chrMmxextFilterCode = av_malloc(c->chrMmxextFilterCodeSize);#endif#ifdef MAP_ANONYMOUS if (c->lumMmxextFilterCode == MAP_FAILED || c->chrMmxextFilterCode == MAP_FAILED)#else if (!c->lumMmxextFilterCode || !c->chrMmxextFilterCode)#endif { av_log(c, AV_LOG_ERROR, "Failed to allocate MMX2FilterCode\n"); return AVERROR(ENOMEM); } FF_ALLOCZ_OR_GOTO(c, c->hLumFilter, (dstW / 8 + 8) * sizeof(int16_t), fail); FF_ALLOCZ_OR_GOTO(c, c->hChrFilter, (c->chrDstW / 4 + 8) * sizeof(int16_t), fail); FF_ALLOCZ_OR_GOTO(c, c->hLumFilterPos, (dstW / 2 / 8 + 8) * sizeof(int32_t), fail); FF_ALLOCZ_OR_GOTO(c, c->hChrFilterPos, (c->chrDstW / 2 / 4 + 8) * sizeof(int32_t), fail); ff_init_hscaler_mmxext( dstW, c->lumXInc, c->lumMmxextFilterCode, c->hLumFilter, (uint32_t*)c->hLumFilterPos, 8); ff_init_hscaler_mmxext(c->chrDstW, c->chrXInc, c->chrMmxextFilterCode, c->hChrFilter, (uint32_t*)c->hChrFilterPos, 4);#if USE_MMAP if ( mprotect(c->lumMmxextFilterCode, c->lumMmxextFilterCodeSize, PROT_EXEC | PROT_READ) == -1 || mprotect(c->chrMmxextFilterCode, c->chrMmxextFilterCodeSize, PROT_EXEC | PROT_READ) == -1) { av_log(c, AV_LOG_ERROR, "mprotect failed, cannot use fast bilinear scaler\n"); goto fail; }#endif } else#endif /* HAVE_MMXEXT_INLINE */ { const int filterAlign = X86_MMX(cpu_flags) ? 4 : PPC_ALTIVEC(cpu_flags) ? 8 : 1; if ((ret = initFilter(&c->hLumFilter, &c->hLumFilterPos, &c->hLumFilterSize, c->lumXInc, srcW, dstW, filterAlign, 1 << 14, (flags & SWS_BICUBLIN) ? (flags | SWS_BICUBIC) : flags, cpu_flags, srcFilter->lumH, dstFilter->lumH, c->param, get_local_pos(c, 0, 0, 0), get_local_pos(c, 0, 0, 0))) < 0) goto fail; if ((ret = initFilter(&c->hChrFilter, &c->hChrFilterPos, &c->hChrFilterSize, c->chrXInc, c->chrSrcW, c->chrDstW, filterAlign, 1 << 14, (flags & SWS_BICUBLIN) ? (flags | SWS_BILINEAR) : flags, cpu_flags, srcFilter->chrH, dstFilter->chrH, c->param, get_local_pos(c, c->chrSrcHSubSample, c->src_h_chr_pos, 0), get_local_pos(c, c->chrDstHSubSample, c->dst_h_chr_pos, 0))) < 0) goto fail; } } // initialize horizontal stuff /* precalculate vertical scaler filter coefficients */ { const int filterAlign = X86_MMX(cpu_flags) ? 2 : PPC_ALTIVEC(cpu_flags) ? 8 : 1; if ((ret = initFilter(&c->vLumFilter, &c->vLumFilterPos, &c->vLumFilterSize, c->lumYInc, srcH, dstH, filterAlign, (1 << 12), (flags & SWS_BICUBLIN) ? (flags | SWS_BICUBIC) : flags, cpu_flags, srcFilter->lumV, dstFilter->lumV, c->param, get_local_pos(c, 0, 0, 1), get_local_pos(c, 0, 0, 1))) < 0) goto fail; if ((ret = initFilter(&c->vChrFilter, &c->vChrFilterPos, &c->vChrFilterSize, c->chrYInc, c->chrSrcH, c->chrDstH, filterAlign, (1 << 12), (flags & SWS_BICUBLIN) ? (flags | SWS_BILINEAR) : flags, cpu_flags, srcFilter->chrV, dstFilter->chrV, c->param, get_local_pos(c, c->chrSrcVSubSample, c->src_v_chr_pos, 1), get_local_pos(c, c->chrDstVSubSample, c->dst_v_chr_pos, 1))) < 0) goto fail;#if HAVE_ALTIVEC FF_ALLOC_OR_GOTO(c, c->vYCoeffsBank, sizeof(vector signed short) * c->vLumFilterSize * c->dstH, fail); FF_ALLOC_OR_GOTO(c, c->vCCoeffsBank, sizeof(vector signed short) * c->vChrFilterSize * c->chrDstH, fail); for (i = 0; i < c->vLumFilterSize * c->dstH; i++) { int j; short *p = (short *)&c->vYCoeffsBank[i]; for (j = 0; j < 8; j++) p[j] = c->vLumFilter[i]; } for (i = 0; i < c->vChrFilterSize * c->chrDstH; i++) { int j; short *p = (short *)&c->vCCoeffsBank[i]; for (j = 0; j < 8; j++) p[j] = c->vChrFilter[i]; }#endif } // calculate buffer sizes so that they won't run out while handling these damn slices c->vLumBufSize = c->vLumFilterSize; c->vChrBufSize = c->vChrFilterSize; for (i = 0; i < dstH; i++) { int chrI = (int64_t)i * c->chrDstH / dstH; int nextSlice = FFMAX(c->vLumFilterPos[i] + c->vLumFilterSize - 1, ((c->vChrFilterPos[chrI] + c->vChrFilterSize - 1) << c->chrSrcVSubSample)); nextSlice >>= c->chrSrcVSubSample; nextSlice <<= c->chrSrcVSubSample; if (c->vLumFilterPos[i] + c->vLumBufSize < nextSlice) c->vLumBufSize = nextSlice - c->vLumFilterPos[i]; if (c->vChrFilterPos[chrI] + c->vChrBufSize < (nextSlice >> c->chrSrcVSubSample)) c->vChrBufSize = (nextSlice >> c->chrSrcVSubSample) - c->vChrFilterPos[chrI]; } for (i = 0; i < 4; i++) FF_ALLOCZ_OR_GOTO(c, c->dither_error[i], (c->dstW+2) * sizeof(int), fail); /* Allocate pixbufs (we use dynamic allocation because otherwise we would * need to allocate several megabytes to handle all possible cases) */ FF_ALLOC_OR_GOTO(c, c->lumPixBuf, c->vLumBufSize * 3 * sizeof(int16_t *), fail); FF_ALLOC_OR_GOTO(c, c->chrUPixBuf, c->vChrBufSize * 3 * sizeof(int16_t *), fail); FF_ALLOC_OR_GOTO(c, c->chrVPixBuf, c->vChrBufSize * 3 * sizeof(int16_t *), fail); if (CONFIG_SWSCALE_ALPHA && isALPHA(c->srcFormat) && isALPHA(c->dstFormat)) FF_ALLOCZ_OR_GOTO(c, c->alpPixBuf, c->vLumBufSize * 3 * sizeof(int16_t *), fail); /* Note we need at least one pixel more at the end because of the MMX code * (just in case someone wants to replace the 4000/8000). */ /* align at 16 bytes for AltiVec */ for (i = 0; i < c->vLumBufSize; i++) { FF_ALLOCZ_OR_GOTO(c, c->lumPixBuf[i + c->vLumBufSize], dst_stride + 16, fail); c->lumPixBuf[i] = c->lumPixBuf[i + c->vLumBufSize]; } // 64 / c->scalingBpp is the same as 16 / sizeof(scaling_intermediate) c->uv_off = (dst_stride>>1) + 64 / (c->dstBpc &~ 7); c->uv_offx2 = dst_stride + 16; for (i = 0; i < c->vChrBufSize; i++) { FF_ALLOC_OR_GOTO(c, c->chrUPixBuf[i + c->vChrBufSize], dst_stride * 2 + 32, fail); c->chrUPixBuf[i] = c->chrUPixBuf[i + c->vChrBufSize]; c->chrVPixBuf[i] = c->chrVPixBuf[i + c->vChrBufSize] = c->chrUPixBuf[i] + (dst_stride >> 1) + 8; } if (CONFIG_SWSCALE_ALPHA && c->alpPixBuf) for (i = 0; i < c->vLumBufSize; i++) { FF_ALLOCZ_OR_GOTO(c, c->alpPixBuf[i + c->vLumBufSize], dst_stride + 16, fail); c->alpPixBuf[i] = c->alpPixBuf[i + c->vLumBufSize]; } // try to avoid drawing green stuff between the right end and the stride end for (i = 0; i < c->vChrBufSize; i++) if(desc_dst->comp[0].depth_minus1 == 15){ av_assert0(c->dstBpc > 14); for(j=0; j<dst_stride/2+1; j++) ((int32_t*)(c->chrUPixBuf[i]))[j] = 1<<18; } else for(j=0; j<dst_stride+1; j++) ((int16_t*)(c->chrUPixBuf[i]))[j] = 1<<14; av_assert0(c->chrDstH <= dstH); //是否要输出 if (flags & SWS_PRINT_INFO) { const char *scaler = NULL, *cpucaps; for (i = 0; i < FF_ARRAY_ELEMS(scale_algorithms); i++) { if (flags & scale_algorithms[i].flag) { scaler = scale_algorithms[i].description; break; } } if (!scaler) scaler = "ehh flags invalid?!"; av_log(c, AV_LOG_INFO, "%s scaler, from %s to %s%s ", scaler, av_get_pix_fmt_name(srcFormat),#ifdef DITHER1XBPP dstFormat == AV_PIX_FMT_BGR555 || dstFormat == AV_PIX_FMT_BGR565 || dstFormat == AV_PIX_FMT_RGB444BE || dstFormat == AV_PIX_FMT_RGB444LE || dstFormat == AV_PIX_FMT_BGR444BE || dstFormat == AV_PIX_FMT_BGR444LE ? "dithered " : "",#else "",#endif av_get_pix_fmt_name(dstFormat)); if (INLINE_MMXEXT(cpu_flags)) cpucaps = "MMXEXT"; else if (INLINE_AMD3DNOW(cpu_flags)) cpucaps = "3DNOW"; else if (INLINE_MMX(cpu_flags)) cpucaps = "MMX"; else if (PPC_ALTIVEC(cpu_flags)) cpucaps = "AltiVec"; else cpucaps = "C"; av_log(c, AV_LOG_INFO, "using %s\n", cpucaps); av_log(c, AV_LOG_VERBOSE, "%dx%d -> %dx%d\n", srcW, srcH, dstW, dstH); av_log(c, AV_LOG_DEBUG, "lum srcW=%d srcH=%d dstW=%d dstH=%d xInc=%d yInc=%d\n", c->srcW, c->srcH, c->dstW, c->dstH, c->lumXInc, c->lumYInc); av_log(c, AV_LOG_DEBUG, "chr srcW=%d srcH=%d dstW=%d dstH=%d xInc=%d yInc=%d\n", c->chrSrcW, c->chrSrcH, c->chrDstW, c->chrDstH, c->chrXInc, c->chrYInc); } /* unscaled special cases */ //不拉伸的情况 if (unscaled && !usesHFilter && !usesVFilter && (c->srcRange == c->dstRange || isAnyRGB(dstFormat))) { //不许拉伸的情况下，初始化相应的函数 ff_get_unscaled_swscale(c); if (c->swscale) { if (flags & SWS_PRINT_INFO) av_log(c, AV_LOG_INFO, "using unscaled %s -> %s special converter\n", av_get_pix_fmt_name(srcFormat), av_get_pix_fmt_name(dstFormat)); return 0; } } //关键：设置SwsContext中的swscale()指针 c->swscale = ff_getSwsFunc(c); return 0;fail: // FIXME replace things by appropriate error codes if (ret == RETCODE_USE_CASCADE) { int tmpW = sqrt(srcW * (int64_t)dstW); int tmpH = sqrt(srcH * (int64_t)dstH); enum AVPixelFormat tmpFormat = AV_PIX_FMT_YUV420P; if (srcW*(int64_t)srcH <= 4LL*dstW*dstH) return AVERROR(EINVAL); ret = av_image_alloc(c->cascaded_tmp, c->cascaded_tmpStride, tmpW, tmpH, tmpFormat, 64); if (ret < 0) return ret; c->cascaded_context[0] = sws_getContext(srcW, srcH, srcFormat, tmpW, tmpH, tmpFormat, flags, srcFilter, NULL, c->param); if (!c->cascaded_context[0]) return -1; c->cascaded_context[1] = sws_getContext(tmpW, tmpH, tmpFormat, dstW, dstH, dstFormat, flags, NULL, dstFilter, c->param); if (!c->cascaded_context[1]) return -1; return 0; } return -1;}sws_init_context()除了对SwsContext中的各种变量进行赋值之外，主要按照顺序完成了以下一些工作：
1. 通过sws_rgb2rgb_init()初始化RGB转RGB（或者YUV转YUV）的函数（注意不包含RGB与YUV相互转换的函数）。
2. 通过判断输入输出图像的宽高来判断图像是否需要拉伸。如果图像需要拉伸，那么unscaled变量会被标记为1。
3. 通过sws_setColorspaceDetails()初始化颜色空间。
4. 一些输入参数的检测。例如：如果没有设置图像拉伸方法的话，默认设置为SWS_BICUBIC；如果输入和输出图像的宽高小于等于0的话，也会返回错误信息。
5. 初始化Filter。这一步根据拉伸方法的不同，初始化不同的Filter。
6. 如果flags中设置了“打印信息”选项SWS_PRINT_INFO，则输出信息。
7. 如果不需要拉伸的话，调用ff_get_unscaled_swscale()将特定的像素转换函数的指针赋值给SwsContext中的swscale指针。
8. 如果需要拉伸的话，调用ff_getSwsFunc()将通用的swscale()赋值给SwsContext中的swscale指针（这个地方有点绕，但是确实是这样的）。
下面分别记录一下上述步骤的实现。
sws_rgb2rgb_init()
sws_rgb2rgb_init()的定义位于libswscale\rgb2rgb.c，如下所示。av_cold void sws_rgb2rgb_init(void){ rgb2rgb_init_c(); if (ARCH_X86) rgb2rgb_init_x86();}从sws_rgb2rgb_init()代码中可以看出，有两个初始化函数：rgb2rgb_init_c()是初始化C语言版本的RGB互转（或者YUV互转）的函数，rgb2rgb_init_x86()则是初始化X86汇编版本的RGB互转的函数。
PS：在libswscale中有一点需要注意：很多的函数名称中包含类似“_c”这样的字符串，代表了该函数是C语言写的。与之对应的还有其它标记，比如“_mmx”，“sse2”等。
rgb2rgb_init_c()
首先来看一下C语言版本的RGB互转函数的初始化函数rgb2rgb_init_c()，定义位于libswscale\rgb2rgb_template.c，如下所示。static av_cold void rgb2rgb_init_c(void){ rgb15to16 = rgb15to16_c; rgb15tobgr24 = rgb15tobgr24_c; rgb15to32 = rgb15to32_c; rgb16tobgr24 = rgb16tobgr24_c; rgb16to32 = rgb16to32_c; rgb16to15 = rgb16to15_c; rgb24tobgr16 = rgb24tobgr16_c; rgb24tobgr15 = rgb24tobgr15_c; rgb24tobgr32 = rgb24tobgr32_c; rgb32to16 = rgb32to16_c; rgb32to15 = rgb32to15_c; rgb32tobgr24 = rgb32tobgr24_c; rgb24to15 = rgb24to15_c; rgb24to16 = rgb24to16_c; rgb24tobgr24 = rgb24tobgr24_c; shuffle_bytes_2103 = shuffle_bytes_2103_c; rgb32tobgr16 = rgb32tobgr16_c; rgb32tobgr15 = rgb32tobgr15_c; yv12toyuy2 = yv12toyuy2_c; yv12touyvy = yv12touyvy_c; yuv422ptoyuy2 = yuv422ptoyuy2_c; yuv422ptouyvy = yuv422ptouyvy_c; yuy2toyv12 = yuy2toyv12_c; planar2x = planar2x_c; ff_rgb24toyv12 = ff_rgb24toyv12_c; interleaveBytes = interleaveBytes_c; deinterleaveBytes = deinterleaveBytes_c; vu9_to_vu12 = vu9_to_vu12_c; yvu9_to_yuy2 = yvu9_to_yuy2_c; uyvytoyuv420 = uyvytoyuv420_c; uyvytoyuv422 = uyvytoyuv422_c; yuyvtoyuv420 = yuyvtoyuv420_c; yuyvtoyuv422 = yuyvtoyuv422_c;}可以看出rgb2rgb_init_c()执行后，会把C语言版本的图像格式转换函数赋值给系统的函数指针。
下面我们选择几个函数看一下这些转换函数的定义。
rgb24tobgr24_c()
rgb24tobgr24_c()完成了RGB24向BGR24格式的转换。函数的定义如下所示。从代码中可以看出，该函数实现了“R”与“B”之间位置的对调，从而完成了这两种格式之间的转换。static inline void rgb24tobgr24_c(const uint8_t *src, uint8_t *dst, int src_size){ unsigned i; for (i = 0; i < src_size; i += 3) { register uint8_t x = src[i + 2]; dst[i + 1] = src[i + 1]; dst[i + 2] = src[i + 0]; dst[i + 0] = x; }}rgb24to16_c()
rgb24to16_c()完成了RGB24向RGB16像素格式的转换。函数的定义如下所示。static inline void rgb24to16_c(const uint8_t *src, uint8_t *dst, int src_size){ uint16_t *d = (uint16_t *)dst; const uint8_t *s = src; const uint8_t *end = s + src_size; while (s < end) { const int r = *s++; const int g = *s++; const int b = *s++; *d++ = (b >> 3) | ((g & 0xFC) << 3) | ((r & 0xF8) << 8); }}yuyvtoyuv422_c()
yuyvtoyuv422_c()完成了YUYV向YUV422像素格式的转换。函数的定义如下所示。static void yuyvtoyuv422_c(uint8_t *ydst, uint8_t *udst, uint8_t *vdst, const uint8_t *src, int width, int height, int lumStride, int chromStride, int srcStride){ int y; const int chromWidth = FF_CEIL_RSHIFT(width, 1); for (y = 0; y < height; y++) { extract_even_c(src, ydst, width); extract_odd2_c(src, udst, vdst, chromWidth); src += srcStride; ydst += lumStride; udst += chromStride; vdst += chromStride; }}该函数将YUYV像素数据分离成为Y，U，V三个分量的像素数据。其中extract_even_c()用于获取一行像素中序数为偶数的像素，对应提取了YUYV像素格式中的“Y”。extract_odd2_c()用于获取一行像素中序数为奇数的像素，并且把这些像素值再次按照奇偶的不同，存储于两个数组中。对应提取了YUYV像素格式中的“U”和“V”。
extract_even_c()定义如下所示。
static void extract_even_c(const uint8_t *src, uint8_t *dst, int count){ dst += count; src += count * 2; count = -count; while (count < 0) { dst[count] = src[2 * count]; count++; }}extract_odd2_c()定义如下所示。 static void extract_even2_c(const uint8_t *src, uint8_t *dst0, uint8_t *dst1, int count){ dst0 += count; dst1 += count; src += count * 4; count = -count; while (count < 0) { dst0[count] = src[4 * count + 0]; dst1[count] = src[4 * count + 2]; count++; }}rgb2rgb_init_x86()
rgb2rgb_init_x86()用于初始化基于X86汇编语言的RGB互转的代码。由于对汇编不是很熟，不再作详细分析，出于和rgb2rgb_init_c()相对比的目的，列出它的代码。它的代码位于libswscale\x86\rgb2rgb.c，如下所示。PS：所有和汇编有关的代码都位于libswscale目录的x86子目录下。
av_cold void rgb2rgb_init_x86(void){#if HAVE_INLINE_ASM int cpu_flags = av_get_cpu_flags(); if (INLINE_MMX(cpu_flags)) rgb2rgb_init_mmx(); if (INLINE_AMD3DNOW(cpu_flags)) rgb2rgb_init_3dnow(); if (INLINE_MMXEXT(cpu_flags)) rgb2rgb_init_mmxext(); if (INLINE_SSE2(cpu_flags)) rgb2rgb_init_sse2(); if (INLINE_AVX(cpu_flags)) rgb2rgb_init_avx();#endif /* HAVE_INLINE_ASM */}可以看出，rgb2rgb_init_x86()首先调用了av_get_cpu_flags()获取CPU支持的特性，根据特性调用rgb2rgb_init_mmx()，rgb2rgb_init_3dnow()，rgb2rgb_init_mmxext()，rgb2rgb_init_sse2()，rgb2rgb_init_avx()等函数。
2.判断图像是否需要拉伸。
这一步主要通过比较输入图像和输出图像的宽高实现。系统使用一个unscaled变量记录图像是否需要拉伸，如下所示。unscaled = (srcW == dstW && srcH == dstH);
3.初始化颜色空间。
初始化颜色空间通过函数sws_setColorspaceDetails()完成。sws_setColorspaceDetails()是FFmpeg的一个API函数，它的声明如下所示：/** * @param dstRange flag indicating the while-black range of the output (1=jpeg / 0=mpeg) * @param srcRange flag indicating the while-black range of the input (1=jpeg / 0=mpeg) * @param table the yuv2rgb coefficients describing the output yuv space, normally ff_yuv2rgb_coeffs[x] * @param inv_table the yuv2rgb coefficients describing the input yuv space, normally ff_yuv2rgb_coeffs[x] * @param brightness 16.16 fixed point brightness correction * @param contrast 16.16 fixed point contrast correction * @param saturation 16.16 fixed point saturation correction * @return -1 if not supported */int sws_setColorspaceDetails(struct SwsContext *c, const int inv_table[4], int srcRange, const int table[4], int dstRange, int brightness, int contrast, int saturation);
简单解释一下几个参数的含义：
c：需要设定的SwsContext。
inv_table：描述输出YUV颜色空间的参数表。
srcRange：输入图像的取值范围（“1”代表JPEG标准，取值范围是0-255；“0”代表MPEG标准，取值范围是16-235）。
table：描述输入YUV颜色空间的参数表。
dstRange：输出图像的取值范围。
brightness：未研究。
contrast：未研究。
saturation：未研究。 如果返回-1代表设置不成功。
其中描述颜色空间的参数表可以通过sws_getCoefficients()获取。该函数在后文中再详细记录。
sws_setColorspaceDetails()的定义位于libswscale\utils.c，如下所示。
int sws_setColorspaceDetails(struct SwsContext *c, const int inv_table[4], int srcRange, const int table[4], int dstRange, int brightness, int contrast, int saturation){ const AVPixFmtDescriptor *desc_dst; const AVPixFmtDescriptor *desc_src; int need_reinit = 0; memmove(c->srcColorspaceTable, inv_table, sizeof(int) * 4); memmove(c->dstColorspaceTable, table, sizeof(int) * 4); handle_formats(c); desc_dst = av_pix_fmt_desc_get(c->dstFormat); desc_src = av_pix_fmt_desc_get(c->srcFormat); if(!isYUV(c->dstFormat) && !isGray(c->dstFormat)) dstRange = 0; if(!isYUV(c->srcFormat) && !isGray(c->srcFormat)) srcRange = 0; c->brightness = brightness; c->contrast = contrast; c->saturation = saturation; if (c->srcRange != srcRange || c->dstRange != dstRange) need_reinit = 1; c->srcRange = srcRange; c->dstRange = dstRange; //The srcBpc check is possibly wrong but we seem to lack a definitive reference to test this //and what we have in ticket 2939 looks better with this check if (need_reinit && (c->srcBpc == 8 || !isYUV(c->srcFormat))) ff_sws_init_range_convert(c); if ((isYUV(c->dstFormat) || isGray(c->dstFormat)) && (isYUV(c->srcFormat) || isGray(c->srcFormat))) return -1; c->dstFormatBpp = av_get_bits_per_pixel(desc_dst); c->srcFormatBpp = av_get_bits_per_pixel(desc_src); if (!isYUV(c->dstFormat) && !isGray(c->dstFormat)) { ff_yuv2rgb_c_init_tables(c, inv_table, srcRange, brightness, contrast, saturation); // FIXME factorize if (ARCH_PPC) ff_yuv2rgb_init_tables_ppc(c, inv_table, brightness, contrast, saturation); } fill_rgb2yuv_table(c, table, dstRange); return 0;}从sws_setColorspaceDetails()定义中可以看出，该函数将输入的参数分别赋值给了相应的变量，并且在最后调用了一个函数fill_rgb2yuv_table()。fill_rgb2yuv_table()函数还没有弄懂，暂时不记录。
sws_getCoefficients()
sws_getCoefficients()用于获取描述颜色空间的参数表。它的声明如下。/** * Return a pointer to yuv<->rgb coefficients for the given colorspace * suitable for sws_setColorspaceDetails(). * * @param colorspace One of the SWS_CS_* macros. If invalid, * SWS_CS_DEFAULT is used. */const int *sws_getCoefficients(int colorspace);
其中colorspace可以取值如下变量。默认的取值SWS_CS_DEFAULT等同于SWS_CS_ITU601或者SWS_CS_SMPTE170M。
#define SWS_CS_ITU709 1#define SWS_CS_FCC 4#define SWS_CS_ITU601 5#define SWS_CS_ITU624 5#define SWS_CS_SMPTE170M 5#define SWS_CS_SMPTE240M 7#define SWS_CS_DEFAULT 5
下面看一下sws_getCoefficients()的定义，位于libswscale\yuv2rgb.c，如下所示。
const int *sws_getCoefficients(int colorspace){ if (colorspace > 7 || colorspace < 0) colorspace = SWS_CS_DEFAULT; return ff_yuv2rgb_coeffs[colorspace];}可以看出它返回了一个名称为ff_yuv2rgb_coeffs的数组中的一个元素，该数组的定义如下所示。
const int32_t ff_yuv2rgb_coeffs[8][4] = { { 117504, 138453, 13954, 34903 }, /* no sequence_display_extension */ { 117504, 138453, 13954, 34903 }, /* ITU-R Rec. 709 (1990) */ { 104597, 132201, 25675, 53279 }, /* unspecified */ { 104597, 132201, 25675, 53279 }, /* reserved */ { 104448, 132798, 24759, 53109 }, /* FCC */ { 104597, 132201, 25675, 53279 }, /* ITU-R Rec. 624-4 System B, G */ { 104597, 132201, 25675, 53279 }, /* SMPTE 170M */ { 117579, 136230, 16907, 35559 } /* SMPTE 240M (1987) */};4.一些输入参数的检测。
例如：如果没有设置图像拉伸方法的话，默认设置为SWS_BICUBIC；如果输入和输出图像的宽高小于等于0的话，也会返回错误信息。有关这方面的代码比较多，简单举个例子。 i = flags & (SWS_POINT | SWS_AREA | SWS_BILINEAR | SWS_FAST_BILINEAR | SWS_BICUBIC | SWS_X | SWS_GAUSS | SWS_LANCZOS | SWS_SINC | SWS_SPLINE | SWS_BICUBLIN); /* provide a default scaler if not set by caller */ if (!i) { if (dstW < srcW && dstH < srcH) flags |= SWS_BICUBIC; else if (dstW > srcW && dstH > srcH) flags |= SWS_BICUBIC; else flags |= SWS_BICUBIC; c->flags = flags; } else if (i & (i - 1)) { av_log(c, AV_LOG_ERROR, "Exactly one scaler algorithm must be chosen, got %X\n", i); return AVERROR(EINVAL); } /* sanity check */ if (srcW < 1 || srcH < 1 || dstW < 1 || dstH < 1) { /* FIXME check if these are enough and try to lower them after * fixing the relevant parts of the code */ av_log(c, AV_LOG_ERROR, "%dx%d -> %dx%d is invalid scaling dimension\n", srcW, srcH, dstW, dstH); return AVERROR(EINVAL); }5.初始化Filter。这一步根据拉伸方法的不同，初始化不同的Filter。
这一部分的工作在函数initFilter()中完成，暂时不详细分析。
6.如果flags中设置了“打印信息”选项SWS_PRINT_INFO，则输出信息。
SwsContext初始化的时候，可以给flags设置SWS_PRINT_INFO标记。这样SwsContext初始化完成的时候就可以打印出一些配置信息。与打印相关的代码如下所示。if (flags & SWS_PRINT_INFO) { const char *scaler = NULL, *cpucaps; for (i = 0; i < FF_ARRAY_ELEMS(scale_algorithms); i++) { if (flags & scale_algorithms[i].flag) { scaler = scale_algorithms[i].description; break; } } if (!scaler) scaler = "ehh flags invalid?!"; av_log(c, AV_LOG_INFO, "%s scaler, from %s to %s%s ", scaler, av_get_pix_fmt_name(srcFormat),#ifdef DITHER1XBPP dstFormat == AV_PIX_FMT_BGR555 || dstFormat == AV_PIX_FMT_BGR565 || dstFormat == AV_PIX_FMT_RGB444BE || dstFormat == AV_PIX_FMT_RGB444LE || dstFormat == AV_PIX_FMT_BGR444BE || dstFormat == AV_PIX_FMT_BGR444LE ? "dithered " : "",#else "",#endif av_get_pix_fmt_name(dstFormat)); if (INLINE_MMXEXT(cpu_flags)) cpucaps = "MMXEXT"; else if (INLINE_AMD3DNOW(cpu_flags)) cpucaps = "3DNOW"; else if (INLINE_MMX(cpu_flags)) cpucaps = "MMX"; else if (PPC_ALTIVEC(cpu_flags)) cpucaps = "AltiVec"; else cpucaps = "C"; av_log(c, AV_LOG_INFO, "using %s\n", cpucaps); av_log(c, AV_LOG_VERBOSE, "%dx%d -> %dx%d\n", srcW, srcH, dstW, dstH); av_log(c, AV_LOG_DEBUG, "lum srcW=%d srcH=%d dstW=%d dstH=%d xInc=%d yInc=%d\n", c->srcW, c->srcH, c->dstW, c->dstH, c->lumXInc, c->lumYInc); av_log(c, AV_LOG_DEBUG, "chr srcW=%d srcH=%d dstW=%d dstH=%d xInc=%d yInc=%d\n", c->chrSrcW, c->chrSrcH, c->chrDstW, c->chrDstH, c->chrXInc, c->chrYInc); }7.如果不需要拉伸的话，就会调用ff_get_unscaled_swscale()将特定的像素转换函数的指针赋值给SwsContext中的swscale指针。
ff_get_unscaled_swscale()
ff_get_unscaled_swscale()的定义如下所示。该函数根据输入图像像素格式和输出图像像素格式，选择不同的像素格式转换函数。
void ff_get_unscaled_swscale(SwsContext *c){ const enum AVPixelFormat srcFormat = c->srcFormat; const enum AVPixelFormat dstFormat = c->dstFormat; const int flags = c->flags; const int dstH = c->dstH; int needsDither; needsDither = isAnyRGB(dstFormat) && c->dstFormatBpp < 24 && (c->dstFormatBpp < c->srcFormatBpp || (!isAnyRGB(srcFormat))); /* yv12_to_nv12 */ if ((srcFormat == AV_PIX_FMT_YUV420P || srcFormat == AV_PIX_FMT_YUVA420P) && (dstFormat == AV_PIX_FMT_NV12 || dstFormat == AV_PIX_FMT_NV21)) { c->swscale = planarToNv12Wrapper; } /* nv12_to_yv12 */ if (dstFormat == AV_PIX_FMT_YUV420P && (srcFormat == AV_PIX_FMT_NV12 || srcFormat == AV_PIX_FMT_NV21)) { c->swscale = nv12ToPlanarWrapper; } /* yuv2bgr */ if ((srcFormat == AV_PIX_FMT_YUV420P || srcFormat == AV_PIX_FMT_YUV422P || srcFormat == AV_PIX_FMT_YUVA420P) && isAnyRGB(dstFormat) && !(flags & SWS_ACCURATE_RND) && (c->dither == SWS_DITHER_BAYER || c->dither == SWS_DITHER_AUTO) && !(dstH & 1)) { c->swscale = ff_yuv2rgb_get_func_ptr(c); } if (srcFormat == AV_PIX_FMT_YUV410P && !(dstH & 3) && (dstFormat == AV_PIX_FMT_YUV420P || dstFormat == AV_PIX_FMT_YUVA420P) && !(flags & SWS_BITEXACT)) { c->swscale = yvu9ToYv12Wrapper; } /* bgr24toYV12 */ if (srcFormat == AV_PIX_FMT_BGR24 && (dstFormat == AV_PIX_FMT_YUV420P || dstFormat == AV_PIX_FMT_YUVA420P) && !(flags & SWS_ACCURATE_RND)) c->swscale = bgr24ToYv12Wrapper; /* RGB/BGR -> RGB/BGR (no dither needed forms) */ if (isAnyRGB(srcFormat) && isAnyRGB(dstFormat) && findRgbConvFn(c) && (!needsDither || (c->flags&(SWS_FAST_BILINEAR|SWS_POINT)))) c->swscale = rgbToRgbWrapper; if ((srcFormat == AV_PIX_FMT_GBRP && dstFormat == AV_PIX_FMT_GBRAP) || (srcFormat == AV_PIX_FMT_GBRAP && dstFormat == AV_PIX_FMT_GBRP)) c->swscale = planarRgbToplanarRgbWrapper;#define isByteRGB(f) ( \ f == AV_PIX_FMT_RGB32 || \ f == AV_PIX_FMT_RGB32_1 || \ f == AV_PIX_FMT_RGB24 || \ f == AV_PIX_FMT_BGR32 || \ f == AV_PIX_FMT_BGR32_1 || \ f == AV_PIX_FMT_BGR24) if (srcFormat == AV_PIX_FMT_GBRP && isPlanar(srcFormat) && isByteRGB(dstFormat)) c->swscale = planarRgbToRgbWrapper; if ((srcFormat == AV_PIX_FMT_RGB48LE || srcFormat == AV_PIX_FMT_RGB48BE || srcFormat == AV_PIX_FMT_BGR48LE || srcFormat == AV_PIX_FMT_BGR48BE || srcFormat == AV_PIX_FMT_RGBA64LE || srcFormat == AV_PIX_FMT_RGBA64BE || srcFormat == AV_PIX_FMT_BGRA64LE || srcFormat == AV_PIX_FMT_BGRA64BE) && (dstFormat == AV_PIX_FMT_GBRP9LE || dstFormat == AV_PIX_FMT_GBRP9BE || dstFormat == AV_PIX_FMT_GBRP10LE || dstFormat == AV_PIX_FMT_GBRP10BE || dstFormat == AV_PIX_FMT_GBRP12LE || dstFormat == AV_PIX_FMT_GBRP12BE || dstFormat == AV_PIX_FMT_GBRP14LE || dstFormat == AV_PIX_FMT_GBRP14BE || dstFormat == AV_PIX_FMT_GBRP16LE || dstFormat == AV_PIX_FMT_GBRP16BE || dstFormat == AV_PIX_FMT_GBRAP16LE || dstFormat == AV_PIX_FMT_GBRAP16BE )) c->swscale = Rgb16ToPlanarRgb16Wrapper; if ((srcFormat == AV_PIX_FMT_GBRP9LE || srcFormat == AV_PIX_FMT_GBRP9BE || srcFormat == AV_PIX_FMT_GBRP16LE || srcFormat == AV_PIX_FMT_GBRP16BE || srcFormat == AV_PIX_FMT_GBRP10LE || srcFormat == AV_PIX_FMT_GBRP10BE || srcFormat == AV_PIX_FMT_GBRP12LE || srcFormat == AV_PIX_FMT_GBRP12BE || srcFormat == AV_PIX_FMT_GBRP14LE || srcFormat == AV_PIX_FMT_GBRP14BE || srcFormat == AV_PIX_FMT_GBRAP16LE || srcFormat == AV_PIX_FMT_GBRAP16BE) && (dstFormat == AV_PIX_FMT_RGB48LE || dstFormat == AV_PIX_FMT_RGB48BE || dstFormat == AV_PIX_FMT_BGR48LE || dstFormat == AV_PIX_FMT_BGR48BE || dstFormat == AV_PIX_FMT_RGBA64LE || dstFormat == AV_PIX_FMT_RGBA64BE || dstFormat == AV_PIX_FMT_BGRA64LE || dstFormat == AV_PIX_FMT_BGRA64BE)) c->swscale = planarRgb16ToRgb16Wrapper; if (av_pix_fmt_desc_get(srcFormat)->comp[0].depth_minus1 == 7 && isPackedRGB(srcFormat) && dstFormat == AV_PIX_FMT_GBRP) c->swscale = rgbToPlanarRgbWrapper; if (isBayer(srcFormat)) { if (dstFormat == AV_PIX_FMT_RGB24) c->swscale = bayer_to_rgb24_wrapper; else if (dstFormat == AV_PIX_FMT_YUV420P) c->swscale = bayer_to_yv12_wrapper; else if (!isBayer(dstFormat)) { av_log(c, AV_LOG_ERROR, "unsupported bayer conversion\n"); av_assert0(0); } } /* bswap 16 bits per pixel/component packed formats */ if (IS_DIFFERENT_ENDIANESS(srcFormat, dstFormat, AV_PIX_FMT_BAYER_BGGR16) || IS_DIFFERENT_ENDIANESS(srcFormat, dstFormat, AV_PIX_FMT_BAYER_RGGB16) || IS_DIFFERENT_ENDIANESS(srcFormat, dstFormat, AV_PIX_FMT_BAYER_GBRG16) || IS_DIFFERENT_ENDIANESS(srcFormat, dstFormat, AV_PIX_FMT_BAYER_GRBG16) || IS_DIFFERENT_ENDIANESS(srcFormat, dstFormat, AV_PIX_FMT_BGR444) || IS_DIFFERENT_ENDIANESS(srcFormat, dstFormat, AV_PIX_FMT_BGR48) || IS_DIFFERENT_ENDIANESS(srcFormat, dstFormat, AV_PIX_FMT_BGRA64) || IS_DIFFERENT_ENDIANESS(srcFormat, dstFormat, AV_PIX_FMT_BGR555) || IS_DIFFERENT_ENDIANESS(srcFormat, dstFormat, AV_PIX_FMT_BGR565) || IS_DIFFERENT_ENDIANESS(srcFormat, dstFormat, AV_PIX_FMT_BGRA64) || IS_DIFFERENT_ENDIANESS(srcFormat, dstFormat, AV_PIX_FMT_GRAY16) || IS_DIFFERENT_ENDIANESS(srcFormat, dstFormat, AV_PIX_FMT_YA16) || IS_DIFFERENT_ENDIANESS(srcFormat, dstFormat, AV_PIX_FMT_GBRP9) || IS_DIFFERENT_ENDIANESS(srcFormat, dstFormat, AV_PIX_FMT_GBRP10) || IS_DIFFERENT_ENDIANESS(srcFormat, dstFormat, AV_PIX_FMT_GBRP12) || IS_DIFFERENT_ENDIANESS(srcFormat, dstFormat, AV_PIX_FMT_GBRP14) || IS_DIFFERENT_ENDIANESS(srcFormat, dstFormat, AV_PIX_FMT_GBRP16) || IS_DIFFERENT_ENDIANESS(srcFormat, dstFormat, AV_PIX_FMT_GBRAP16) || IS_DIFFERENT_ENDIANESS(srcFormat, dstFormat, AV_PIX_FMT_RGB444) || IS_DIFFERENT_ENDIANESS(srcFormat, dstFormat, AV_PIX_FMT_RGB48) || IS_DIFFERENT_ENDIANESS(srcFormat, dstFormat, AV_PIX_FMT_RGBA64) || IS_DIFFERENT_ENDIANESS(srcFormat, dstFormat, AV_PIX_FMT_RGB555) || IS_DIFFERENT_ENDIANESS(srcFormat, dstFormat, AV_PIX_FMT_RGB565) || IS_DIFFERENT_ENDIANESS(srcFormat, dstFormat, AV_PIX_FMT_RGBA64) || IS_DIFFERENT_ENDIANESS(srcFormat, dstFormat, AV_PIX_FMT_XYZ12) || IS_DIFFERENT_ENDIANESS(srcFormat, dstFormat, AV_PIX_FMT_YUV420P9) || IS_DIFFERENT_ENDIANESS(srcFormat, dstFormat, AV_PIX_FMT_YUV420P10) || IS_DIFFERENT_ENDIANESS(srcFormat, dstFormat, AV_PIX_FMT_YUV420P12) || IS_DIFFERENT_ENDIANESS(srcFormat, dstFormat, AV_PIX_FMT_YUV420P14) || IS_DIFFERENT_ENDIANESS(srcFormat, dstFormat, AV_PIX_FMT_YUV420P16) || IS_DIFFERENT_ENDIANESS(srcFormat, dstFormat, AV_PIX_FMT_YUV422P9) || IS_DIFFERENT_ENDIANESS(srcFormat, dstFormat, AV_PIX_FMT_YUV422P10) || IS_DIFFERENT_ENDIANESS(srcFormat, dstFormat, AV_PIX_FMT_YUV422P12) || IS_DIFFERENT_ENDIANESS(srcFormat, dstFormat, AV_PIX_FMT_YUV422P14) || IS_DIFFERENT_ENDIANESS(srcFormat, dstFormat, AV_PIX_FMT_YUV422P16) || IS_DIFFERENT_ENDIANESS(srcFormat, dstFormat, AV_PIX_FMT_YUV444P9) || IS_DIFFERENT_ENDIANESS(srcFormat, dstFormat, AV_PIX_FMT_YUV444P10) || IS_DIFFERENT_ENDIANESS(srcFormat, dstFormat, AV_PIX_FMT_YUV444P12) || IS_DIFFERENT_ENDIANESS(srcFormat, dstFormat, AV_PIX_FMT_YUV444P14) || IS_DIFFERENT_ENDIANESS(srcFormat, dstFormat, AV_PIX_FMT_YUV444P16)) c->swscale = packed_16bpc_bswap; if (usePal(srcFormat) && isByteRGB(dstFormat)) c->swscale = palToRgbWrapper; if (srcFormat == AV_PIX_FMT_YUV422P) { if (dstFormat == AV_PIX_FMT_YUYV422) c->swscale = yuv422pToYuy2Wrapper; else if (dstFormat == AV_PIX_FMT_UYVY422) c->swscale = yuv422pToUyvyWrapper; } /* LQ converters if -sws 0 or -sws 4*/ if (c->flags&(SWS_FAST_BILINEAR|SWS_POINT)) { /* yv12_to_yuy2 */ if (srcFormat == AV_PIX_FMT_YUV420P || srcFormat == AV_PIX_FMT_YUVA420P) { if (dstFormat == AV_PIX_FMT_YUYV422) c->swscale = planarToYuy2Wrapper; else if (dstFormat == AV_PIX_FMT_UYVY422) c->swscale = planarToUyvyWrapper; } } if (srcFormat == AV_PIX_FMT_YUYV422 && (dstFormat == AV_PIX_FMT_YUV420P || dstFormat == AV_PIX_FMT_YUVA420P)) c->swscale = yuyvToYuv420Wrapper; if (srcFormat == AV_PIX_FMT_UYVY422 && (dstFormat == AV_PIX_FMT_YUV420P || dstFormat == AV_PIX_FMT_YUVA420P)) c->swscale = uyvyToYuv420Wrapper; if (srcFormat == AV_PIX_FMT_YUYV422 && dstFormat == AV_PIX_FMT_YUV422P) c->swscale = yuyvToYuv422Wrapper; if (srcFormat == AV_PIX_FMT_UYVY422 && dstFormat == AV_PIX_FMT_YUV422P) c->swscale = uyvyToYuv422Wrapper;#define isPlanarGray(x) (isGray(x) && (x) != AV_PIX_FMT_YA8 && (x) != AV_PIX_FMT_YA16LE && (x) != AV_PIX_FMT_YA16BE) /* simple copy */ if ( srcFormat == dstFormat || (srcFormat == AV_PIX_FMT_YUVA420P && dstFormat == AV_PIX_FMT_YUV420P) || (srcFormat == AV_PIX_FMT_YUV420P && dstFormat == AV_PIX_FMT_YUVA420P) || (isPlanarYUV(srcFormat) && isPlanarGray(dstFormat)) || (isPlanarYUV(dstFormat) && isPlanarGray(srcFormat)) || (isPlanarGray(dstFormat) && isPlanarGray(srcFormat)) || (isPlanarYUV(srcFormat) && isPlanarYUV(dstFormat) && c->chrDstHSubSample == c->chrSrcHSubSample && c->chrDstVSubSample == c->chrSrcVSubSample && dstFormat != AV_PIX_FMT_NV12 && dstFormat != AV_PIX_FMT_NV21 && srcFormat != AV_PIX_FMT_NV12 && srcFormat != AV_PIX_FMT_NV21)) { if (isPacked(c->srcFormat)) c->swscale = packedCopyWrapper; else /* Planar YUV or gray */ c->swscale = planarCopyWrapper; } if (ARCH_PPC) ff_get_unscaled_swscale_ppc(c);// if (ARCH_ARM)// ff_get_unscaled_swscale_arm(c);}从ff_get_unscaled_swscale()源代码中可以看出，赋值给SwsContext的swscale指针的函数名称大多数为XXXWrapper()。实际上这些函数封装了一些基本的像素格式转换函数。例如yuyvToYuv422Wrapper()的定义如下所示。
static int yuyvToYuv422Wrapper(SwsContext *c, const uint8_t *src[], int srcStride[], int srcSliceY, int srcSliceH, uint8_t *dstParam[], int dstStride[]){ uint8_t *ydst = dstParam[0] + dstStride[0] * srcSliceY; uint8_t *udst = dstParam[1] + dstStride[1] * srcSliceY; uint8_t *vdst = dstParam[2] + dstStride[2] * srcSliceY; yuyvtoyuv422(ydst, udst, vdst, src[0], c->srcW, srcSliceH, dstStride[0], dstStride[1], srcStride[0]); return srcSliceH;}从yuyvToYuv422Wrapper()的定义中可以看出，它调用了yuyvtoyuv422()。而yuyvtoyuv422()则是rgb2rgb.c中的一个函数，用于将YUVU转换为YUV422（该函数在前文中已经记录）。
8.如果需要拉伸的话，就会调用ff_getSwsFunc()将通用的swscale()赋值给SwsContext中的swscale指针，然后返回。
上一步骤（图像不用缩放）实际上是一种不太常见的情况，更多的情况下会执行本步骤。这个时候就会调用ff_getSwsFunc()获取图像的缩放函数。
ff_getSwsFunc()
ff_getSwsFunc()用于获取通用的swscale()函数。该函数的定义如下。SwsFunc ff_getSwsFunc(SwsContext *c){ sws_init_swscale(c); if (ARCH_PPC) ff_sws_init_swscale_ppc(c); if (ARCH_X86) ff_sws_init_swscale_x86(c); return swscale;}从源代码中可以看出ff_getSwsFunc()调用了函数sws_init_swscale()。如果系统支持X86汇编的话，还会调用ff_sws_init_swscale_x86()。
sws_init_swscale()
sws_init_swscale()的定义位于libswscale\swscale.c，如下所示。
static av_cold void sws_init_swscale(SwsContext *c){ enum AVPixelFormat srcFormat = c->srcFormat; ff_sws_init_output_funcs(c, &c->yuv2plane1, &c->yuv2planeX, &c->yuv2nv12cX, &c->yuv2packed1, &c->yuv2packed2, &c->yuv2packedX, &c->yuv2anyX); ff_sws_init_input_funcs(c); if (c->srcBpc == 8) { if (c->dstBpc <= 14) { c->hyScale = c->hcScale = hScale8To15_c; if (c->flags & SWS_FAST_BILINEAR) { c->hyscale_fast = ff_hyscale_fast_c; c->hcscale_fast = ff_hcscale_fast_c; } } else { c->hyScale = c->hcScale = hScale8To19_c; } } else { c->hyScale = c->hcScale = c->dstBpc > 14 ? hScale16To19_c : hScale16To15_c; } ff_sws_init_range_convert(c); if (!(isGray(srcFormat) || isGray(c->dstFormat) || srcFormat == AV_PIX_FMT_MONOBLACK || srcFormat == AV_PIX_FMT_MONOWHITE)) c->needs_hcscale = 1;}从函数中可以看出，sws_init_swscale()主要调用了3个函数：ff_sws_init_output_funcs()，ff_sws_init_input_funcs()，ff_sws_init_range_convert()。其中，ff_sws_init_output_funcs()用于初始化输出的函数，ff_sws_init_input_funcs()用于初始化输入的函数，ff_sws_init_range_convert()用于初始化像素值范围转换的函数。
ff_sws_init_output_funcs()
ff_sws_init_output_funcs()用于初始化“输出函数”。“输出函数”在libswscale中的作用就是将处理后的一行像素数据输出出来。ff_sws_init_output_funcs()的定义位于libswscale\output.c，如下所示。
av_cold void ff_sws_init_output_funcs(SwsContext *c, yuv2planar1_fn *yuv2plane1, yuv2planarX_fn *yuv2planeX, yuv2interleavedX_fn *yuv2nv12cX, yuv2packed1_fn *yuv2packed1, yuv2packed2_fn *yuv2packed2, yuv2packedX_fn *yuv2packedX, yuv2anyX_fn *yuv2anyX){ enum AVPixelFormat dstFormat = c->dstFormat; const AVPixFmtDescriptor *desc = av_pix_fmt_desc_get(dstFormat); if (is16BPS(dstFormat)) { *yuv2planeX = isBE(dstFormat) ? yuv2planeX_16BE_c : yuv2planeX_16LE_c; *yuv2plane1 = isBE(dstFormat) ? yuv2plane1_16BE_c : yuv2plane1_16LE_c; } else if (is9_OR_10BPS(dstFormat)) { if (desc->comp[0].depth_minus1 == 8) { *yuv2planeX = isBE(dstFormat) ? yuv2planeX_9BE_c : yuv2planeX_9LE_c; *yuv2plane1 = isBE(dstFormat) ? yuv2plane1_9BE_c : yuv2plane1_9LE_c; } else if (desc->comp[0].depth_minus1 == 9) { *yuv2planeX = isBE(dstFormat) ? yuv2planeX_10BE_c : yuv2planeX_10LE_c; *yuv2plane1 = isBE(dstFormat) ? yuv2plane1_10BE_c : yuv2plane1_10LE_c; } else if (desc->comp[0].depth_minus1 == 11) { *yuv2planeX = isBE(dstFormat) ? yuv2planeX_12BE_c : yuv2planeX_12LE_c; *yuv2plane1 = isBE(dstFormat) ? yuv2plane1_12BE_c : yuv2plane1_12LE_c; } else if (desc->comp[0].depth_minus1 == 13) { *yuv2planeX = isBE(dstFormat) ? yuv2planeX_14BE_c : yuv2planeX_14LE_c; *yuv2plane1 = isBE(dstFormat) ? yuv2plane1_14BE_c : yuv2plane1_14LE_c; } else av_assert0(0); } else { *yuv2plane1 = yuv2plane1_8_c; *yuv2planeX = yuv2planeX_8_c; if (dstFormat == AV_PIX_FMT_NV12 || dstFormat == AV_PIX_FMT_NV21) *yuv2nv12cX = yuv2nv12cX_c; } if(c->flags & SWS_FULL_CHR_H_INT) { switch (dstFormat) { case AV_PIX_FMT_RGBA:#if CONFIG_SMALL *yuv2packedX = yuv2rgba32_full_X_c; *yuv2packed2 = yuv2rgba32_full_2_c; *yuv2packed1 = yuv2rgba32_full_1_c;#else#if CONFIG_SWSCALE_ALPHA if (c->alpPixBuf) { *yuv2packedX = yuv2rgba32_full_X_c; *yuv2packed2 = yuv2rgba32_full_2_c; *yuv2packed1 = yuv2rgba32_full_1_c; } else#endif /* CONFIG_SWSCALE_ALPHA */ { *yuv2packedX = yuv2rgbx32_full_X_c; *yuv2packed2 = yuv2rgbx32_full_2_c; *yuv2packed1 = yuv2rgbx32_full_1_c; }#endif /* !CONFIG_SMALL */ break; case AV_PIX_FMT_ARGB:#if CONFIG_SMALL *yuv2packedX = yuv2argb32_full_X_c; *yuv2packed2 = yuv2argb32_full_2_c; *yuv2packed1 = yuv2argb32_full_1_c;#else#if CONFIG_SWSCALE_ALPHA if (c->alpPixBuf) { *yuv2packedX = yuv2argb32_full_X_c; *yuv2packed2 = yuv2argb32_full_2_c; *yuv2packed1 = yuv2argb32_full_1_c; } else#endif /* CONFIG_SWSCALE_ALPHA */ { *yuv2packedX = yuv2xrgb32_full_X_c; *yuv2packed2 = yuv2xrgb32_full_2_c; *yuv2packed1 = yuv2xrgb32_full_1_c; }#endif /* !CONFIG_SMALL */ break; case AV_PIX_FMT_BGRA:#if CONFIG_SMALL *yuv2packedX = yuv2bgra32_full_X_c; *yuv2packed2 = yuv2bgra32_full_2_c; *yuv2packed1 = yuv2bgra32_full_1_c;#else#if CONFIG_SWSCALE_ALPHA if (c->alpPixBuf) { *yuv2packedX = yuv2bgra32_full_X_c; *yuv2packed2 = yuv2bgra32_full_2_c; *yuv2packed1 = yuv2bgra32_full_1_c; } else#endif /* CONFIG_SWSCALE_ALPHA */ { *yuv2packedX = yuv2bgrx32_full_X_c; *yuv2packed2 = yuv2bgrx32_full_2_c; *yuv2packed1 = yuv2bgrx32_full_1_c; }#endif /* !CONFIG_SMALL */ break; case AV_PIX_FMT_ABGR:#if CONFIG_SMALL *yuv2packedX = yuv2abgr32_full_X_c; *yuv2packed2 = yuv2abgr32_full_2_c; *yuv2packed1 = yuv2abgr32_full_1_c;#else#if CONFIG_SWSCALE_ALPHA if (c->alpPixBuf) { *yuv2packedX = yuv2abgr32_full_X_c; *yuv2packed2 = yuv2abgr32_full_2_c; *yuv2packed1 = yuv2abgr32_full_1_c; } else#endif /* CONFIG_SWSCALE_ALPHA */ { *yuv2packedX = yuv2xbgr32_full_X_c; *yuv2packed2 = yuv2xbgr32_full_2_c; *yuv2packed1 = yuv2xbgr32_full_1_c; }#endif /* !CONFIG_SMALL */ break; case AV_PIX_FMT_RGB24: *yuv2packedX = yuv2rgb24_full_X_c; *yuv2packed2 = yuv2rgb24_full_2_c; *yuv2packed1 = yuv2rgb24_full_1_c; break; case AV_PIX_FMT_BGR24: *yuv2packedX = yuv2bgr24_full_X_c; *yuv2packed2 = yuv2bgr24_full_2_c; *yuv2packed1 = yuv2bgr24_full_1_c; break; case AV_PIX_FMT_BGR4_BYTE: *yuv2packedX = yuv2bgr4_byte_full_X_c; *yuv2packed2 = yuv2bgr4_byte_full_2_c; *yuv2packed1 = yuv2bgr4_byte_full_1_c; break; case AV_PIX_FMT_RGB4_BYTE: *yuv2packedX = yuv2rgb4_byte_full_X_c; *yuv2packed2 = yuv2rgb4_byte_full_2_c; *yuv2packed1 = yuv2rgb4_byte_full_1_c; break; case AV_PIX_FMT_BGR8: *yuv2packedX = yuv2bgr8_full_X_c; *yuv2packed2 = yuv2bgr8_full_2_c; *yuv2packed1 = yuv2bgr8_full_1_c; break; case AV_PIX_FMT_RGB8: *yuv2packedX = yuv2rgb8_full_X_c; *yuv2packed2 = yuv2rgb8_full_2_c; *yuv2packed1 = yuv2rgb8_full_1_c; break; case AV_PIX_FMT_GBRP: case AV_PIX_FMT_GBRP9BE: case AV_PIX_FMT_GBRP9LE: case AV_PIX_FMT_GBRP10BE: case AV_PIX_FMT_GBRP10LE: case AV_PIX_FMT_GBRP12BE: case AV_PIX_FMT_GBRP12LE: case AV_PIX_FMT_GBRP14BE: case AV_PIX_FMT_GBRP14LE: case AV_PIX_FMT_GBRP16BE: case AV_PIX_FMT_GBRP16LE: case AV_PIX_FMT_GBRAP: *yuv2anyX = yuv2gbrp_full_X_c; break; } if (!*yuv2packedX && !*yuv2anyX) goto YUV_PACKED; } else { YUV_PACKED: switch (dstFormat) { case AV_PIX_FMT_RGBA64LE:#if CONFIG_SWSCALE_ALPHA if (c->alpPixBuf) { *yuv2packed1 = yuv2rgba64le_1_c; *yuv2packed2 = yuv2rgba64le_2_c; *yuv2packedX = yuv2rgba64le_X_c; } else#endif /* CONFIG_SWSCALE_ALPHA */ { *yuv2packed1 = yuv2rgbx64le_1_c; *yuv2packed2 = yuv2rgbx64le_2_c; *yuv2packedX = yuv2rgbx64le_X_c; } break; case AV_PIX_FMT_RGBA64BE:#if CONFIG_SWSCALE_ALPHA if (c->alpPixBuf) { *yuv2packed1 = yuv2rgba64be_1_c; *yuv2packed2 = yuv2rgba64be_2_c; *yuv2packedX = yuv2rgba64be_X_c; } else#endif /* CONFIG_SWSCALE_ALPHA */ { *yuv2packed1 = yuv2rgbx64be_1_c; *yuv2packed2 = yuv2rgbx64be_2_c; *yuv2packedX = yuv2rgbx64be_X_c; } break; case AV_PIX_FMT_BGRA64LE:#if CONFIG_SWSCALE_ALPHA if (c->alpPixBuf) { *yuv2packed1 = yuv2bgra64le_1_c; *yuv2packed2 = yuv2bgra64le_2_c; *yuv2packedX = yuv2bgra64le_X_c; } else#endif /* CONFIG_SWSCALE_ALPHA */ { *yuv2packed1 = yuv2bgrx64le_1_c; *yuv2packed2 = yuv2bgrx64le_2_c; *yuv2packedX = yuv2bgrx64le_X_c; } break; case AV_PIX_FMT_BGRA64BE:#if CONFIG_SWSCALE_ALPHA if (c->alpPixBuf) { *yuv2packed1 = yuv2bgra64be_1_c; *yuv2packed2 = yuv2bgra64be_2_c; *yuv2packedX = yuv2bgra64be_X_c; } else#endif /* CONFIG_SWSCALE_ALPHA */ { *yuv2packed1 = yuv2bgrx64be_1_c; *yuv2packed2 = yuv2bgrx64be_2_c; *yuv2packedX = yuv2bgrx64be_X_c; } break; case AV_PIX_FMT_RGB48LE: *yuv2packed1 = yuv2rgb48le_1_c; *yuv2packed2 = yuv2rgb48le_2_c; *yuv2packedX = yuv2rgb48le_X_c; break; case AV_PIX_FMT_RGB48BE: *yuv2packed1 = yuv2rgb48be_1_c; *yuv2packed2 = yuv2rgb48be_2_c; *yuv2packedX = yuv2rgb48be_X_c; break; case AV_PIX_FMT_BGR48LE: *yuv2packed1 = yuv2bgr48le_1_c; *yuv2packed2 = yuv2bgr48le_2_c; *yuv2packedX = yuv2bgr48le_X_c; break; case AV_PIX_FMT_BGR48BE: *yuv2packed1 = yuv2bgr48be_1_c; *yuv2packed2 = yuv2bgr48be_2_c; *yuv2packedX = yuv2bgr48be_X_c; break; case AV_PIX_FMT_RGB32: case AV_PIX_FMT_BGR32:#if CONFIG_SMALL *yuv2packed1 = yuv2rgb32_1_c; *yuv2packed2 = yuv2rgb32_2_c; *yuv2packedX = yuv2rgb32_X_c;#else#if CONFIG_SWSCALE_ALPHA if (c->alpPixBuf) { *yuv2packed1 = yuv2rgba32_1_c; *yuv2packed2 = yuv2rgba32_2_c; *yuv2packedX = yuv2rgba32_X_c; } else#endif /* CONFIG_SWSCALE_ALPHA */ { *yuv2packed1 = yuv2rgbx32_1_c; *yuv2packed2 = yuv2rgbx32_2_c; *yuv2packedX = yuv2rgbx32_X_c; }#endif /* !CONFIG_SMALL */ break; case AV_PIX_FMT_RGB32_1: case AV_PIX_FMT_BGR32_1:#if CONFIG_SMALL *yuv2packed1 = yuv2rgb32_1_1_c; *yuv2packed2 = yuv2rgb32_1_2_c; *yuv2packedX = yuv2rgb32_1_X_c;#else#if CONFIG_SWSCALE_ALPHA if (c->alpPixBuf) { *yuv2packed1 = yuv2rgba32_1_1_c; *yuv2packed2 = yuv2rgba32_1_2_c; *yuv2packedX = yuv2rgba32_1_X_c; } else#endif /* CONFIG_SWSCALE_ALPHA */ { *yuv2packed1 = yuv2rgbx32_1_1_c; *yuv2packed2 = yuv2rgbx32_1_2_c; *yuv2packedX = yuv2rgbx32_1_X_c; }#endif /* !CONFIG_SMALL */ break; case AV_PIX_FMT_RGB24: *yuv2packed1 = yuv2rgb24_1_c; *yuv2packed2 = yuv2rgb24_2_c; *yuv2packedX = yuv2rgb24_X_c; break; case AV_PIX_FMT_BGR24: *yuv2packed1 = yuv2bgr24_1_c; *yuv2packed2 = yuv2bgr24_2_c; *yuv2packedX = yuv2bgr24_X_c; break; case AV_PIX_FMT_RGB565LE: case AV_PIX_FMT_RGB565BE: case AV_PIX_FMT_BGR565LE: case AV_PIX_FMT_BGR565BE: *yuv2packed1 = yuv2rgb16_1_c; *yuv2packed2 = yuv2rgb16_2_c; *yuv2packedX = yuv2rgb16_X_c; break; case AV_PIX_FMT_RGB555LE: case AV_PIX_FMT_RGB555BE: case AV_PIX_FMT_BGR555LE: case AV_PIX_FMT_BGR555BE: *yuv2packed1 = yuv2rgb15_1_c; *yuv2packed2 = yuv2rgb15_2_c; *yuv2packedX = yuv2rgb15_X_c; break; case AV_PIX_FMT_RGB444LE: case AV_PIX_FMT_RGB444BE: case AV_PIX_FMT_BGR444LE: case AV_PIX_FMT_BGR444BE: *yuv2packed1 = yuv2rgb12_1_c; *yuv2packed2 = yuv2rgb12_2_c; *yuv2packedX = yuv2rgb12_X_c; break; case AV_PIX_FMT_RGB8: case AV_PIX_FMT_BGR8: *yuv2packed1 = yuv2rgb8_1_c; *yuv2packed2 = yuv2rgb8_2_c; *yuv2packedX = yuv2rgb8_X_c; break; case AV_PIX_FMT_RGB4: case AV_PIX_FMT_BGR4: *yuv2packed1 = yuv2rgb4_1_c; *yuv2packed2 = yuv2rgb4_2_c; *yuv2packedX = yuv2rgb4_X_c; break; case AV_PIX_FMT_RGB4_BYTE: case AV_PIX_FMT_BGR4_BYTE: *yuv2packed1 = yuv2rgb4b_1_c; *yuv2packed2 = yuv2rgb4b_2_c; *yuv2packedX = yuv2rgb4b_X_c; break; } } switch (dstFormat) { case AV_PIX_FMT_MONOWHITE: *yuv2packed1 = yuv2monowhite_1_c; *yuv2packed2 = yuv2monowhite_2_c; *yuv2packedX = yuv2monowhite_X_c; break; case AV_PIX_FMT_MONOBLACK: *yuv2packed1 = yuv2monoblack_1_c; *yuv2packed2 = yuv2monoblack_2_c; *yuv2packedX = yuv2monoblack_X_c; break; case AV_PIX_FMT_YUYV422: *yuv2packed1 = yuv2yuyv422_1_c; *yuv2packed2 = yuv2yuyv422_2_c; *yuv2packedX = yuv2yuyv422_X_c; break; case AV_PIX_FMT_YVYU422: *yuv2packed1 = yuv2yvyu422_1_c; *yuv2packed2 = yuv2yvyu422_2_c; *yuv2packedX = yuv2yvyu422_X_c; break; case AV_PIX_FMT_UYVY422: *yuv2packed1 = yuv2uyvy422_1_c; *yuv2packed2 = yuv2uyvy422_2_c; *yuv2packedX = yuv2uyvy422_X_c; break; }}ff_sws_init_output_funcs()根据输出像素格式的不同，对以下几个函数指针进行赋值：
yuv2plane1：是yuv2planar1_fn类型的函数指针。该函数用于输出一行水平拉伸后的planar格式数据。数据没有使用垂直拉伸。
yuv2planeX：是yuv2planarX_fn类型的函数指针。该函数用于输出一行水平拉伸后的planar格式数据。数据使用垂直拉伸。
yuv2packed1：是yuv2packed1_fn类型的函数指针。该函数用于输出一行水平拉伸后的packed格式数据。数据没有使用垂直拉伸。
yuv2packed2：是yuv2packed2_fn类型的函数指针。该函数用于输出一行水平拉伸后的packed格式数据。数据使用两行数据进行垂直拉伸。
yuv2packedX：是yuv2packedX_fn类型的函数指针。该函数用于输出一行水平拉伸后的packed格式数据。数据使用垂直拉伸。
yuv2nv12cX：是yuv2interleavedX_fn类型的函数指针。还没有研究该函数。
yuv2anyX：是yuv2anyX_fn类型的函数指针。还没有研究该函数。
ff_sws_init_input_funcs()
ff_sws_init_input_funcs()用于初始化“输入函数”。“输入函数”在libswscale中的作用就是任意格式的像素转换为YUV格式以供后续的处理。ff_sws_init_input_funcs()的定义位于libswscale\input.c，如下所示。av_cold void ff_sws_init_input_funcs(SwsContext *c){ enum AVPixelFormat srcFormat = c->srcFormat; c->chrToYV12 = NULL; switch (srcFormat) { case AV_PIX_FMT_YUYV422: c->chrToYV12 = yuy2ToUV_c; break; case AV_PIX_FMT_YVYU422: c->chrToYV12 = yvy2ToUV_c; break; case AV_PIX_FMT_UYVY422: c->chrToYV12 = uyvyToUV_c; break; case AV_PIX_FMT_NV12: c->chrToYV12 = nv12ToUV_c; break; case AV_PIX_FMT_NV21: c->chrToYV12 = nv21ToUV_c; break; case AV_PIX_FMT_RGB8: case AV_PIX_FMT_BGR8: case AV_PIX_FMT_PAL8: case AV_PIX_FMT_BGR4_BYTE: case AV_PIX_FMT_RGB4_BYTE: c->chrToYV12 = palToUV_c; break; case AV_PIX_FMT_GBRP9LE: c->readChrPlanar = planar_rgb9le_to_uv; break; case AV_PIX_FMT_GBRP10LE: c->readChrPlanar = planar_rgb10le_to_uv; break; case AV_PIX_FMT_GBRP12LE: c->readChrPlanar = planar_rgb12le_to_uv; break; case AV_PIX_FMT_GBRP14LE: c->readChrPlanar = planar_rgb14le_to_uv; break; case AV_PIX_FMT_GBRAP16LE: case AV_PIX_FMT_GBRP16LE: c->readChrPlanar = planar_rgb16le_to_uv; break; case AV_PIX_FMT_GBRP9BE: c->readChrPlanar = planar_rgb9be_to_uv; break; case AV_PIX_FMT_GBRP10BE: c->readChrPlanar = planar_rgb10be_to_uv; break; case AV_PIX_FMT_GBRP12BE: c->readChrPlanar = planar_rgb12be_to_uv; break; case AV_PIX_FMT_GBRP14BE: c->readChrPlanar = planar_rgb14be_to_uv; break; case AV_PIX_FMT_GBRAP16BE: case AV_PIX_FMT_GBRP16BE: c->readChrPlanar = planar_rgb16be_to_uv; break; case AV_PIX_FMT_GBRAP: case AV_PIX_FMT_GBRP: c->readChrPlanar = planar_rgb_to_uv; break;#if HAVE_BIGENDIAN case AV_PIX_FMT_YUV444P9LE: case AV_PIX_FMT_YUV422P9LE: case AV_PIX_FMT_YUV420P9LE: case AV_PIX_FMT_YUV422P10LE: case AV_PIX_FMT_YUV444P10LE: case AV_PIX_FMT_YUV420P10LE: case AV_PIX_FMT_YUV422P12LE: case AV_PIX_FMT_YUV444P12LE: case AV_PIX_FMT_YUV420P12LE: case AV_PIX_FMT_YUV422P14LE: case AV_PIX_FMT_YUV444P14LE: case AV_PIX_FMT_YUV420P14LE: case AV_PIX_FMT_YUV420P16LE: case AV_PIX_FMT_YUV422P16LE: case AV_PIX_FMT_YUV444P16LE: case AV_PIX_FMT_YUVA444P9LE: case AV_PIX_FMT_YUVA422P9LE: case AV_PIX_FMT_YUVA420P9LE: case AV_PIX_FMT_YUVA444P10LE: case AV_PIX_FMT_YUVA422P10LE: case AV_PIX_FMT_YUVA420P10LE: case AV_PIX_FMT_YUVA420P16LE: case AV_PIX_FMT_YUVA422P16LE: case AV_PIX_FMT_YUVA444P16LE: c->chrToYV12 = bswap16UV_c; break;#else case AV_PIX_FMT_YUV444P9BE: case AV_PIX_FMT_YUV422P9BE: case AV_PIX_FMT_YUV420P9BE: case AV_PIX_FMT_YUV444P10BE: case AV_PIX_FMT_YUV422P10BE: case AV_PIX_FMT_YUV420P10BE: case AV_PIX_FMT_YUV444P12BE: case AV_PIX_FMT_YUV422P12BE: case AV_PIX_FMT_YUV420P12BE: case AV_PIX_FMT_YUV444P14BE: case AV_PIX_FMT_YUV422P14BE: case AV_PIX_FMT_YUV420P14BE: case AV_PIX_FMT_YUV420P16BE: case AV_PIX_FMT_YUV422P16BE: case AV_PIX_FMT_YUV444P16BE: case AV_PIX_FMT_YUVA444P9BE: case AV_PIX_FMT_YUVA422P9BE: case AV_PIX_FMT_YUVA420P9BE: case AV_PIX_FMT_YUVA444P10BE: case AV_PIX_FMT_YUVA422P10BE: case AV_PIX_FMT_YUVA420P10BE: case AV_PIX_FMT_YUVA420P16BE: case AV_PIX_FMT_YUVA422P16BE: case AV_PIX_FMT_YUVA444P16BE: c->chrToYV12 = bswap16UV_c; break;#endif } if (c->chrSrcHSubSample) { switch (srcFormat) { case AV_PIX_FMT_RGBA64BE: c->chrToYV12 = rgb64BEToUV_half_c; break; case AV_PIX_FMT_RGBA64LE: c->chrToYV12 = rgb64LEToUV_half_c; break; case AV_PIX_FMT_BGRA64BE: c->chrToYV12 = bgr64BEToUV_half_c; break; case AV_PIX_FMT_BGRA64LE: c->chrToYV12 = bgr64LEToUV_half_c; break; case AV_PIX_FMT_RGB48BE: c->chrToYV12 = rgb48BEToUV_half_c; break; case AV_PIX_FMT_RGB48LE: c->chrToYV12 = rgb48LEToUV_half_c; break; case AV_PIX_FMT_BGR48BE: c->chrToYV12 = bgr48BEToUV_half_c; break; case AV_PIX_FMT_BGR48LE: c->chrToYV12 = bgr48LEToUV_half_c; break; case AV_PIX_FMT_RGB32: c->chrToYV12 = bgr32ToUV_half_c; break; case AV_PIX_FMT_RGB32_1: c->chrToYV12 = bgr321ToUV_half_c; break; case AV_PIX_FMT_BGR24: c->chrToYV12 = bgr24ToUV_half_c; break; case AV_PIX_FMT_BGR565LE: c->chrToYV12 = bgr16leToUV_half_c; break; case AV_PIX_FMT_BGR565BE: c->chrToYV12 = bgr16beToUV_half_c; break; case AV_PIX_FMT_BGR555LE: c->chrToYV12 = bgr15leToUV_half_c; break; case AV_PIX_FMT_BGR555BE: c->chrToYV12 = bgr15beToUV_half_c; break; case AV_PIX_FMT_GBRAP: case AV_PIX_FMT_GBRP: c->chrToYV12 = gbr24pToUV_half_c; break; case AV_PIX_FMT_BGR444LE: c->chrToYV12 = bgr12leToUV_half_c; break; case AV_PIX_FMT_BGR444BE: c->chrToYV12 = bgr12beToUV_half_c; break; case AV_PIX_FMT_BGR32: c->chrToYV12 = rgb32ToUV_half_c; break; case AV_PIX_FMT_BGR32_1: c->chrToYV12 = rgb321ToUV_half_c; break; case AV_PIX_FMT_RGB24: c->chrToYV12 = rgb24ToUV_half_c; break; case AV_PIX_FMT_RGB565LE: c->chrToYV12 = rgb16leToUV_half_c; break; case AV_PIX_FMT_RGB565BE: c->chrToYV12 = rgb16beToUV_half_c; break; case AV_PIX_FMT_RGB555LE: c->chrToYV12 = rgb15leToUV_half_c; break; case AV_PIX_FMT_RGB555BE: c->chrToYV12 = rgb15beToUV_half_c; break; case AV_PIX_FMT_RGB444LE: c->chrToYV12 = rgb12leToUV_half_c; break; case AV_PIX_FMT_RGB444BE: c->chrToYV12 = rgb12beToUV_half_c; break; } } else { switch (srcFormat) { case AV_PIX_FMT_RGBA64BE: c->chrToYV12 = rgb64BEToUV_c; break; case AV_PIX_FMT_RGBA64LE: c->chrToYV12 = rgb64LEToUV_c; break; case AV_PIX_FMT_BGRA64BE: c->chrToYV12 = bgr64BEToUV_c; break; case AV_PIX_FMT_BGRA64LE: c->chrToYV12 = bgr64LEToUV_c; break; case AV_PIX_FMT_RGB48BE: c->chrToYV12 = rgb48BEToUV_c; break; case AV_PIX_FMT_RGB48LE: c->chrToYV12 = rgb48LEToUV_c; break; case AV_PIX_FMT_BGR48BE: c->chrToYV12 = bgr48BEToUV_c; break; case AV_PIX_FMT_BGR48LE: c->chrToYV12 = bgr48LEToUV_c; break; case AV_PIX_FMT_RGB32: c->chrToYV12 = bgr32ToUV_c; break; case AV_PIX_FMT_RGB32_1: c->chrToYV12 = bgr321ToUV_c; break; case AV_PIX_FMT_BGR24: c->chrToYV12 = bgr24ToUV_c; break; case AV_PIX_FMT_BGR565LE: c->chrToYV12 = bgr16leToUV_c; break; case AV_PIX_FMT_BGR565BE: c->chrToYV12 = bgr16beToUV_c; break; case AV_PIX_FMT_BGR555LE: c->chrToYV12 = bgr15leToUV_c; break; case AV_PIX_FMT_BGR555BE: c->chrToYV12 = bgr15beToUV_c; break; case AV_PIX_FMT_BGR444LE: c->chrToYV12 = bgr12leToUV_c; break; case AV_PIX_FMT_BGR444BE: c->chrToYV12 = bgr12beToUV_c; break; case AV_PIX_FMT_BGR32: c->chrToYV12 = rgb32ToUV_c; break; case AV_PIX_FMT_BGR32_1: c->chrToYV12 = rgb321ToUV_c; break; case AV_PIX_FMT_RGB24: c->chrToYV12 = rgb24ToUV_c; break; case AV_PIX_FMT_RGB565LE: c->chrToYV12 = rgb16leToUV_c; break; case AV_PIX_FMT_RGB565BE: c->chrToYV12 = rgb16beToUV_c; break; case AV_PIX_FMT_RGB555LE: c->chrToYV12 = rgb15leToUV_c; break; case AV_PIX_FMT_RGB555BE: c->chrToYV12 = rgb15beToUV_c; break; case AV_PIX_FMT_RGB444LE: c->chrToYV12 = rgb12leToUV_c; break; case AV_PIX_FMT_RGB444BE: c->chrToYV12 = rgb12beToUV_c; break; } } c->lumToYV12 = NULL; c->alpToYV12 = NULL; switch (srcFormat) { case AV_PIX_FMT_GBRP9LE: c->readLumPlanar = planar_rgb9le_to_y; break; case AV_PIX_FMT_GBRP10LE: c->readLumPlanar = planar_rgb10le_to_y; break; case AV_PIX_FMT_GBRP12LE: c->readLumPlanar = planar_rgb12le_to_y; break; case AV_PIX_FMT_GBRP14LE: c->readLumPlanar = planar_rgb14le_to_y; break; case AV_PIX_FMT_GBRAP16LE: case AV_PIX_FMT_GBRP16LE: c->readLumPlanar = planar_rgb16le_to_y; break; case AV_PIX_FMT_GBRP9BE: c->readLumPlanar = planar_rgb9be_to_y; break; case AV_PIX_FMT_GBRP10BE: c->readLumPlanar = planar_rgb10be_to_y; break; case AV_PIX_FMT_GBRP12BE: c->readLumPlanar = planar_rgb12be_to_y; break; case AV_PIX_FMT_GBRP14BE: c->readLumPlanar = planar_rgb14be_to_y; break; case AV_PIX_FMT_GBRAP16BE: case AV_PIX_FMT_GBRP16BE: c->readLumPlanar = planar_rgb16be_to_y; break; case AV_PIX_FMT_GBRAP: c->readAlpPlanar = planar_rgb_to_a; case AV_PIX_FMT_GBRP: c->readLumPlanar = planar_rgb_to_y; break;#if HAVE_BIGENDIAN case AV_PIX_FMT_YUV444P9LE: case AV_PIX_FMT_YUV422P9LE: case AV_PIX_FMT_YUV420P9LE: case AV_PIX_FMT_YUV444P10LE: case AV_PIX_FMT_YUV422P10LE: case AV_PIX_FMT_YUV420P10LE: case AV_PIX_FMT_YUV444P12LE: case AV_PIX_FMT_YUV422P12LE: case AV_PIX_FMT_YUV420P12LE: case AV_PIX_FMT_YUV444P14LE: case AV_PIX_FMT_YUV422P14LE: case AV_PIX_FMT_YUV420P14LE: case AV_PIX_FMT_YUV420P16LE: case AV_PIX_FMT_YUV422P16LE: case AV_PIX_FMT_YUV444P16LE: case AV_PIX_FMT_GRAY16LE: c->lumToYV12 = bswap16Y_c; break; case AV_PIX_FMT_YUVA444P9LE: case AV_PIX_FMT_YUVA422P9LE: case AV_PIX_FMT_YUVA420P9LE: case AV_PIX_FMT_YUVA444P10LE: case AV_PIX_FMT_YUVA422P10LE: case AV_PIX_FMT_YUVA420P10LE: case AV_PIX_FMT_YUVA420P16LE: case AV_PIX_FMT_YUVA422P16LE: case AV_PIX_FMT_YUVA444P16LE: c->lumToYV12 = bswap16Y_c; c->alpToYV12 = bswap16Y_c; break;#else case AV_PIX_FMT_YUV444P9BE: case AV_PIX_FMT_YUV422P9BE: case AV_PIX_FMT_YUV420P9BE: case AV_PIX_FMT_YUV444P10BE: case AV_PIX_FMT_YUV422P10BE: case AV_PIX_FMT_YUV420P10BE: case AV_PIX_FMT_YUV444P12BE: case AV_PIX_FMT_YUV422P12BE: case AV_PIX_FMT_YUV420P12BE: case AV_PIX_FMT_YUV444P14BE: case AV_PIX_FMT_YUV422P14BE: case AV_PIX_FMT_YUV420P14BE: case AV_PIX_FMT_YUV420P16BE: case AV_PIX_FMT_YUV422P16BE: case AV_PIX_FMT_YUV444P16BE: case AV_PIX_FMT_GRAY16BE: c->lumToYV12 = bswap16Y_c; break; case AV_PIX_FMT_YUVA444P9BE: case AV_PIX_FMT_YUVA422P9BE: case AV_PIX_FMT_YUVA420P9BE: case AV_PIX_FMT_YUVA444P10BE: case AV_PIX_FMT_YUVA422P10BE: case AV_PIX_FMT_YUVA420P10BE: case AV_PIX_FMT_YUVA420P16BE: case AV_PIX_FMT_YUVA422P16BE: case AV_PIX_FMT_YUVA444P16BE: c->lumToYV12 = bswap16Y_c; c->alpToYV12 = bswap16Y_c; break;#endif case AV_PIX_FMT_YA16LE: c->lumToYV12 = read_ya16le_gray_c; c->alpToYV12 = read_ya16le_alpha_c; break; case AV_PIX_FMT_YA16BE: c->lumToYV12 = read_ya16be_gray_c; c->alpToYV12 = read_ya16be_alpha_c; break; case AV_PIX_FMT_YUYV422: case AV_PIX_FMT_YVYU422: case AV_PIX_FMT_YA8: c->lumToYV12 = yuy2ToY_c; break; case AV_PIX_FMT_UYVY422: c->lumToYV12 = uyvyToY_c; break; case AV_PIX_FMT_BGR24: c->lumToYV12 = bgr24ToY_c; break; case AV_PIX_FMT_BGR565LE: c->lumToYV12 = bgr16leToY_c; break; case AV_PIX_FMT_BGR565BE: c->lumToYV12 = bgr16beToY_c; break; case AV_PIX_FMT_BGR555LE: c->lumToYV12 = bgr15leToY_c; break; case AV_PIX_FMT_BGR555BE: c->lumToYV12 = bgr15beToY_c; break; case AV_PIX_FMT_BGR444LE: c->lumToYV12 = bgr12leToY_c; break; case AV_PIX_FMT_BGR444BE: c->lumToYV12 = bgr12beToY_c; break; case AV_PIX_FMT_RGB24: c->lumToYV12 = rgb24ToY_c; break; case AV_PIX_FMT_RGB565LE: c->lumToYV12 = rgb16leToY_c; break; case AV_PIX_FMT_RGB565BE: c->lumToYV12 = rgb16beToY_c; break; case AV_PIX_FMT_RGB555LE: c->lumToYV12 = rgb15leToY_c; break; case AV_PIX_FMT_RGB555BE: c->lumToYV12 = rgb15beToY_c; break; case AV_PIX_FMT_RGB444LE: c->lumToYV12 = rgb12leToY_c; break; case AV_PIX_FMT_RGB444BE: c->lumToYV12 = rgb12beToY_c; break; case AV_PIX_FMT_RGB8: case AV_PIX_FMT_BGR8: case AV_PIX_FMT_PAL8: case AV_PIX_FMT_BGR4_BYTE: case AV_PIX_FMT_RGB4_BYTE: c->lumToYV12 = palToY_c; break; case AV_PIX_FMT_MONOBLACK: c->lumToYV12 = monoblack2Y_c; break; case AV_PIX_FMT_MONOWHITE: c->lumToYV12 = monowhite2Y_c; break; case AV_PIX_FMT_RGB32: c->lumToYV12 = bgr32ToY_c; break; case AV_PIX_FMT_RGB32_1: c->lumToYV12 = bgr321ToY_c; break; case AV_PIX_FMT_BGR32: c->lumToYV12 = rgb32ToY_c; break; case AV_PIX_FMT_BGR32_1: c->lumToYV12 = rgb321ToY_c; break; case AV_PIX_FMT_RGB48BE: c->lumToYV12 = rgb48BEToY_c; break; case AV_PIX_FMT_RGB48LE: c->lumToYV12 = rgb48LEToY_c; break; case AV_PIX_FMT_BGR48BE: c->lumToYV12 = bgr48BEToY_c; break; case AV_PIX_FMT_BGR48LE: c->lumToYV12 = bgr48LEToY_c; break; case AV_PIX_FMT_RGBA64BE: c->lumToYV12 = rgb64BEToY_c; break; case AV_PIX_FMT_RGBA64LE: c->lumToYV12 = rgb64LEToY_c; break; case AV_PIX_FMT_BGRA64BE: c->lumToYV12 = bgr64BEToY_c; break; case AV_PIX_FMT_BGRA64LE: c->lumToYV12 = bgr64LEToY_c; } if (c->alpPixBuf) { if (is16BPS(srcFormat) || isNBPS(srcFormat)) { if (HAVE_BIGENDIAN == !isBE(srcFormat)) c->alpToYV12 = bswap16Y_c; } switch (srcFormat) { case AV_PIX_FMT_BGRA64LE: case AV_PIX_FMT_BGRA64BE: case AV_PIX_FMT_RGBA64LE: case AV_PIX_FMT_RGBA64BE: c->alpToYV12 = rgba64ToA_c; break; case AV_PIX_FMT_BGRA: case AV_PIX_FMT_RGBA: c->alpToYV12 = rgbaToA_c; break; case AV_PIX_FMT_ABGR: case AV_PIX_FMT_ARGB: c->alpToYV12 = abgrToA_c; break; case AV_PIX_FMT_YA8: c->alpToYV12 = uyvyToY_c; break; case AV_PIX_FMT_PAL8 : c->alpToYV12 = palToA_c; break; } }}ff_sws_init_input_funcs()根据输入像素格式的不同，对以下几个函数指针进行赋值：
lumToYV12：转换得到Y分量。
chrToYV12：转换得到UV分量。
alpToYV12：转换得到Alpha分量。
readLumPlanar：读取planar格式的数据转换为Y。
readChrPlanar：读取planar格式的数据转换为UV。
下面看几个例子。
当输入像素格式为AV_PIX_FMT_RGB24的时候，lumToYV12()指针指向的函数是rgb24ToY_c()，如下所示。case AV_PIX_FMT_RGB24: c->lumToYV12 = rgb24ToY_c; break;
rgb24ToY_c()
rgb24ToY_c()的定义如下。
static void rgb24ToY_c(uint8_t *_dst, const uint8_t *src, const uint8_t *unused1, const uint8_t *unused2, int width, uint32_t *rgb2yuv){ int16_t *dst = (int16_t *)_dst; int32_t ry = rgb2yuv[RY_IDX], gy = rgb2yuv[GY_IDX], by = rgb2yuv[BY_IDX]; int i; for (i = 0; i < width; i++) { int r = src[i * 3 + 0]; int g = src[i * 3 + 1]; int b = src[i * 3 + 2]; dst[i] = ((ry*r + gy*g + by*b + (32<<(RGB2YUV_SHIFT-1)) + (1<<(RGB2YUV_SHIFT-7)))>>(RGB2YUV_SHIFT-6)); }}从源代码中可以看出，该函数主要完成了以下三步：
1. 取系数。通过读取rgb2yuv数组中存储的参数获得R，G，B每个分量的系数。
2. 取像素值。分别读取R，G，B每个分量的像素值。
3. 计算得到亮度值。根据R，G，B的系数和值，计算得到亮度值Y。
当输入像素格式为AV_PIX_FMT_RGB24的时候，chrToYV12 ()指针指向的函数是rgb24ToUV_half_c()，如下所示。
case AV_PIX_FMT_RGB24: c->chrToYV12 = rgb24ToUV_half_c; break;
rgb24ToUV_half_c()
rgb24ToUV_half_c()定义如下。static void rgb24ToUV_half_c(uint8_t *_dstU, uint8_t *_dstV, const uint8_t *unused0, const uint8_t *src1, const uint8_t *src2, int width, uint32_t *rgb2yuv){ int16_t *dstU = (int16_t *)_dstU; int16_t *dstV = (int16_t *)_dstV; int i; int32_t ru = rgb2yuv[RU_IDX], gu = rgb2yuv[GU_IDX], bu = rgb2yuv[BU_IDX]; int32_t rv = rgb2yuv[RV_IDX], gv = rgb2yuv[GV_IDX], bv = rgb2yuv[BV_IDX]; av_assert1(src1 == src2); for (i = 0; i < width; i++) { int r = src1[6 * i + 0] + src1[6 * i + 3]; int g = src1[6 * i + 1] + src1[6 * i + 4]; int b = src1[6 * i + 2] + src1[6 * i + 5]; dstU[i] = (ru*r + gu*g + bu*b + (256<<RGB2YUV_SHIFT) + (1<<(RGB2YUV_SHIFT-6)))>>(RGB2YUV_SHIFT-5); dstV[i] = (rv*r + gv*g + bv*b + (256<<RGB2YUV_SHIFT) + (1<<(RGB2YUV_SHIFT-6)))>>(RGB2YUV_SHIFT-5); }}rgb24ToUV_half_c()的过程相比rgb24ToY_c()要稍微复杂些。这主要是因为U，V取值的数量只有Y的一半。因此需要首先求出每2个像素点的平均值之后，再进行计算。
当输入像素格式为AV_PIX_FMT_GBRP（注意这个是planar格式，三个分量分别为G，B，R）的时候，readLumPlanar指向的函数是planar_rgb_to_y()，如下所示。
case AV_PIX_FMT_GBRP: c->readLumPlanar = planar_rgb_to_y; break;
planar_rgb_to_y()
planar_rgb_to_y()定义如下。
static void planar_rgb_to_y(uint8_t *_dst, const uint8_t *src[4], int width, int32_t *rgb2yuv){ uint16_t *dst = (uint16_t *)_dst; int32_t ry = rgb2yuv[RY_IDX], gy = rgb2yuv[GY_IDX], by = rgb2yuv[BY_IDX]; int i; for (i = 0; i < width; i++) { int g = src[0][i]; int b = src[1][i]; int r = src[2][i]; dst[i] = (ry*r + gy*g + by*b + (0x801<<(RGB2YUV_SHIFT-7))) >> (RGB2YUV_SHIFT-6); }}可以看出处理planar格式的GBR数据和处理packed格式的RGB数据的方法是基本一样的，在这里不再重复。
ff_sws_init_range_convert()
ff_sws_init_range_convert()用于初始化像素值范围转换的函数，它的定义位于libswscale\swscale.c，如下所示。av_cold void ff_sws_init_range_convert(SwsContext *c){ c->lumConvertRange = NULL; c->chrConvertRange = NULL; if (c->srcRange != c->dstRange && !isAnyRGB(c->dstFormat)) { if (c->dstBpc <= 14) { if (c->srcRange) { c->lumConvertRange = lumRangeFromJpeg_c; c->chrConvertRange = chrRangeFromJpeg_c; } else { c->lumConvertRange = lumRangeToJpeg_c; c->chrConvertRange = chrRangeToJpeg_c; } } else { if (c->srcRange) { c->lumConvertRange = lumRangeFromJpeg16_c; c->chrConvertRange = chrRangeFromJpeg16_c; } else { c->lumConvertRange = lumRangeToJpeg16_c; c->chrConvertRange = chrRangeToJpeg16_c; } } }}ff_sws_init_range_convert()包含了两种像素取值范围的转换：
lumConvertRange：亮度分量取值范围的转换。
chrConvertRange：色度分量取值范围的转换。
从JPEG标准转换为MPEG标准的函数有：lumRangeFromJpeg_c()和chrRangeFromJpeg_c()。
lumRangeFromJpeg_c()
亮度转换（0-255转换为16-235）函数lumRangeFromJpeg_c()如下所示。static void lumRangeFromJpeg_c(int16_t *dst, int width){ int i; for (i = 0; i < width; i++) dst[i] = (dst[i] * 14071 + 33561947) >> 14;}可以简单代入一个数字验证一下上述函数的正确性。该函数将亮度值“0”映射成“16”，“255”映射成“235”，因此我们可以代入一个“255”看看转换后的数值是否为“235”。在这里需要注意，dst中存储的像素数值是15bit的亮度值。因此我们需要将8bit的数值“255”左移7位后带入。经过计算，255左移7位后取值为32640，计算后得到的数值为30080，右移7位后得到的8bit亮度值即为235。
后续几个函数都可以用上面描述的方法进行验证，就不再重复了。
chrRangeFromJpeg_c()
色度转换（0-255转换为16-240）函数chrRangeFromJpeg_c()如下所示。static void chrRangeFromJpeg_c(int16_t *dstU, int16_t *dstV, int width){ int i; for (i = 0; i < width; i++) { dstU[i] = (dstU[i] * 1799 + 4081085) >> 11; // 1469 dstV[i] = (dstV[i] * 1799 + 4081085) >> 11; // 1469 }}从MPEG标准转换为JPEG标准的函数有：lumRangeToJpeg_c()和chrRangeToJpeg_c()。
lumRangeToJpeg_c()
亮度转换（16-235转换为0-255）函数lumRangeToJpeg_c()定义如下所示。static void lumRangeToJpeg_c(int16_t *dst, int width){ int i; for (i = 0; i < width; i++) dst[i] = (FFMIN(dst[i], 30189) * 19077 - 39057361) >> 14;}chrRangeToJpeg_c()
色度转换（16-240转换为0-255）函数chrRangeToJpeg_c()定义如下所示。static void chrRangeToJpeg_c(int16_t *dstU, int16_t *dstV, int width){ int i; for (i = 0; i < width; i++) { dstU[i] = (FFMIN(dstU[i], 30775) * 4663 - 9289992) >> 12; // -264 dstV[i] = (FFMIN(dstV[i], 30775) * 4663 - 9289992) >> 12; // -264 }}至此sws_getContext()的源代码就基本上分析完毕了。
雷霄骅
leixiaohua1020@126.com
http://blog.csdn.net/leixiaohua1020
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