最简单的基于FFmpeg的libswscale的示例

本文记录一个基于FFmpeg的libswscale的示例。Libswscale里面实现了各种图像像素格式的转换，以及图像大小缩放功能。而且libswscale还做了相应指令集的优化，因此它的转换效率比自己写的C语言的转换效率高很多。

流程

简单的初始化方法

Libswscale使用起来很方便，最主要的函数只有3个：

（1）       sws_getContext()：使用参数初始化SwsContext结构体。

（2）       sws_scale()：转换一帧图像。

（3）       sws_freeContext()：释放SwsContext结构体。

其中sws_getContext()也可以用另一个接口函数sws_getCachedContext()取代。

复杂但是更灵活的初始化方法

初始化SwsContext除了调用sws_getContext()之外还有另一种方法，更加灵活，可以配置更多的参数。该方法调用的函数如下所示。

（1）       sws_alloc_context()：为SwsContext结构体分配内存。

（2）       av_opt_set_XXX()：通过av_opt_set_int()，av_opt_set()…等等一系列方法设置SwsContext结构体的值。在这里需要注意，SwsContext结构体的定义看不到，所以不能对其中的成员变量直接进行赋值，必须通过av_opt_set()这类的API才能对其进行赋值。

（3）       sws_init_context()：初始化SwsContext结构体。

这种复杂的方法可以配置一些sws_getContext()配置不了的参数。比如说设置图像的YUV像素的取值范围是JPEG标准（Y、U、V取值范围都是0-255）还是MPEG标准（Y取值范围是16-235，U、V的取值范围是16-240）。

几个知识点

像素格式

像素格式的知识此前已经记录过，不再重复。在这里记录一下FFmpeg支持的像素格式。有几点注意事项：

（1）       所有的像素格式的名称都是以“AV_PIX_FMT_”开头

（2）       像素格式名称后面有“P”的，代表是planar格式，否则就是packed格式。Planar格式不同的分量分别存储在不同的数组中，例如AV_PIX_FMT_YUV420P存储方式如下：

data[0]: Y1, Y2, Y3, Y4, Y5, Y6, Y7, Y8……

data[1]: U1, U2, U3, U4……

data[2]: V1, V2, V3, V4……

Packed格式的数据都存储在同一个数组中，例如AV_PIX_FMT_RGB24存储方式如下：

data[0]: R1, G1, B1, R2, G2, B2, R3, G3, B3, R4, G4, B4……

（3）       像素格式名称后面有“BE”的，代表是Big Endian格式；名称后面有“LE”的，代表是Little Endian格式。

FFmpeg支持的像素格式的定义位于libavutil\pixfmt.h，是一个名称为AVPixelFormat的枚举类型，如下所示。

/** * Pixel format. * * @note * AV_PIX_FMT_RGB32 is handled in an endian-specific manner. An RGBA * color is put together as: *  (A << 24) | (R << 16) | (G << 8) | B * This is stored as BGRA on little-endian CPU architectures and ARGB on * big-endian CPUs. * * @par * When the pixel format is palettized RGB (AV_PIX_FMT_PAL8), the palettized * image data is stored in AVFrame.data[0]. The palette is transported in * AVFrame.data[1], is 1024 bytes long (256 4-byte entries) and is * formatted the same as in AV_PIX_FMT_RGB32 described above (i.e., it is * also endian-specific). Note also that the individual RGB palette * components stored in AVFrame.data[1] should be in the range 0..255. * This is important as many custom PAL8 video codecs that were designed * to run on the IBM VGA graphics adapter use 6-bit palette components. * * @par * For all the 8bit per pixel formats, an RGB32 palette is in data[1] like * for pal8. This palette is filled in automatically by the function * allocating the picture. * * @note * Make sure that all newly added big-endian formats have (pix_fmt & 1) == 1 * and that all newly added little-endian formats have (pix_fmt & 1) == 0. * This allows simpler detection of big vs little-endian. */enum AVPixelFormat {  AV_PIX_FMT_NONE = -1,  AV_PIX_FMT_YUV420P,   ///< planar YUV 4:2:0, 12bpp, (1 Cr & Cb sample per 2x2 Y samples)  AV_PIX_FMT_YUYV422,   ///< packed YUV 4:2:2, 16bpp, Y0 Cb Y1 Cr  AV_PIX_FMT_RGB24, ///< packed RGB 8:8:8, 24bpp, RGBRGB...  AV_PIX_FMT_BGR24, ///< packed RGB 8:8:8, 24bpp, BGRBGR...  AV_PIX_FMT_YUV422P,   ///< planar YUV 4:2:2, 16bpp, (1 Cr & Cb sample per 2x1 Y samples)  AV_PIX_FMT_YUV444P,   ///< planar YUV 4:4:4, 24bpp, (1 Cr & Cb sample per 1x1 Y samples)  AV_PIX_FMT_YUV410P,   ///< planar YUV 4:1:0,  9bpp, (1 Cr & Cb sample per 4x4 Y samples)  AV_PIX_FMT_YUV411P,   ///< planar YUV 4:1:1, 12bpp, (1 Cr & Cb sample per 4x1 Y samples)  AV_PIX_FMT_GRAY8, ///<Y,  8bpp  AV_PIX_FMT_MONOWHITE, ///<Y,  1bpp, 0 is white, 1 is black, in each byte pixels are ordered from the msb to the lsb  AV_PIX_FMT_MONOBLACK, ///<Y,  1bpp, 0 is black, 1 is white, in each byte pixels are ordered from the msb to the lsb  AV_PIX_FMT_PAL8,  ///< 8 bit with PIX_FMT_RGB32 palette  AV_PIX_FMT_YUVJ420P,  ///< planar YUV 4:2:0, 12bpp, full scale (JPEG), deprecated in favor of PIX_FMT_YUV420P and setting color_range  AV_PIX_FMT_YUVJ422P,  ///< planar YUV 4:2:2, 16bpp, full scale (JPEG), deprecated in favor of PIX_FMT_YUV422P and setting color_range  AV_PIX_FMT_YUVJ444P,  ///< planar YUV 4:4:4, 24bpp, full scale (JPEG), deprecated in favor of PIX_FMT_YUV444P and setting color_range#if FF_API_XVMC  AV_PIX_FMT_XVMC_MPEG2_MC,///< XVideo Motion Acceleration via common packet passing  AV_PIX_FMT_XVMC_MPEG2_IDCT,#define AV_PIX_FMT_XVMC AV_PIX_FMT_XVMC_MPEG2_IDCT#endif /* FF_API_XVMC */  AV_PIX_FMT_UYVY422,   ///< packed YUV 4:2:2, 16bpp, Cb Y0 Cr Y1  AV_PIX_FMT_UYYVYY411, ///< packed YUV 4:1:1, 12bpp, Cb Y0 Y1 Cr Y2 Y3  AV_PIX_FMT_BGR8,  ///< packed RGB 3:3:2,  8bpp, (msb)2B 3G 3R(lsb)  AV_PIX_FMT_BGR4,  ///< packed RGB 1:2:1 bitstream,  4bpp, (msb)1B 2G 1R(lsb), a byte contains two pixels, the first pixel in the byte is the one composed by the 4 msb bits  AV_PIX_FMT_BGR4_BYTE, ///< packed RGB 1:2:1,  8bpp, (msb)1B 2G 1R(lsb)  AV_PIX_FMT_RGB8,  ///< packed RGB 3:3:2,  8bpp, (msb)2R 3G 3B(lsb)  AV_PIX_FMT_RGB4,  ///< packed RGB 1:2:1 bitstream,  4bpp, (msb)1R 2G 1B(lsb), a byte contains two pixels, the first pixel in the byte is the one composed by the 4 msb bits  AV_PIX_FMT_RGB4_BYTE, ///< packed RGB 1:2:1,  8bpp, (msb)1R 2G 1B(lsb)  AV_PIX_FMT_NV12,  ///< planar YUV 4:2:0, 12bpp, 1 plane for Y and 1 plane for the UV components, which are interleaved (first byte U and the following byte V)  AV_PIX_FMT_NV21,  ///< as above, but U and V bytes are swapped  AV_PIX_FMT_ARGB,  ///< packed ARGB 8:8:8:8, 32bpp, ARGBARGB...  AV_PIX_FMT_RGBA,  ///< packed RGBA 8:8:8:8, 32bpp, RGBARGBA...  AV_PIX_FMT_ABGR,  ///< packed ABGR 8:8:8:8, 32bpp, ABGRABGR...  AV_PIX_FMT_BGRA,  ///< packed BGRA 8:8:8:8, 32bpp, BGRABGRA...  AV_PIX_FMT_GRAY16BE,  ///<Y, 16bpp, big-endian  AV_PIX_FMT_GRAY16LE,  ///<Y, 16bpp, little-endian  AV_PIX_FMT_YUV440P,   ///< planar YUV 4:4:0 (1 Cr & Cb sample per 1x2 Y samples)  AV_PIX_FMT_YUVJ440P,  ///< planar YUV 4:4:0 full scale (JPEG), deprecated in favor of PIX_FMT_YUV440P and setting color_range  AV_PIX_FMT_YUVA420P,  ///< planar YUV 4:2:0, 20bpp, (1 Cr & Cb sample per 2x2 Y & A samples)#if FF_API_VDPAU  AV_PIX_FMT_VDPAU_H264,///< H.264 HW decoding with VDPAU, data[0] contains a vdpau_render_state struct which contains the bitstream of the slices as well as various fields extracted from headers  AV_PIX_FMT_VDPAU_MPEG1,///< MPEG-1 HW decoding with VDPAU, data[0] contains a vdpau_render_state struct which contains the bitstream of the slices as well as various fields extracted from headers  AV_PIX_FMT_VDPAU_MPEG2,///< MPEG-2 HW decoding with VDPAU, data[0] contains a vdpau_render_state struct which contains the bitstream of the slices as well as various fields extracted from headers  AV_PIX_FMT_VDPAU_WMV3,///< WMV3 HW decoding with VDPAU, data[0] contains a vdpau_render_state struct which contains the bitstream of the slices as well as various fields extracted from headers  AV_PIX_FMT_VDPAU_VC1, ///< VC-1 HW decoding with VDPAU, data[0] contains a vdpau_render_state struct which contains the bitstream of the slices as well as various fields extracted from headers#endif  AV_PIX_FMT_RGB48BE,   ///< packed RGB 16:16:16, 48bpp, 16R, 16G, 16B, the 2-byte value for each R/G/B component is stored as big-endian  AV_PIX_FMT_RGB48LE,   ///< packed RGB 16:16:16, 48bpp, 16R, 16G, 16B, the 2-byte value for each R/G/B component is stored as little-endian  AV_PIX_FMT_RGB565BE,  ///< packed RGB 5:6:5, 16bpp, (msb)   5R 6G 5B(lsb), big-endian  AV_PIX_FMT_RGB565LE,  ///< packed RGB 5:6:5, 16bpp, (msb)   5R 6G 5B(lsb), little-endian  AV_PIX_FMT_RGB555BE,  ///< packed RGB 5:5:5, 16bpp, (msb)1A 5R 5G 5B(lsb), big-endian, most significant bit to 0  AV_PIX_FMT_RGB555LE,  ///< packed RGB 5:5:5, 16bpp, (msb)1A 5R 5G 5B(lsb), little-endian, most significant bit to 0  AV_PIX_FMT_BGR565BE,  ///< packed BGR 5:6:5, 16bpp, (msb)   5B 6G 5R(lsb), big-endian  AV_PIX_FMT_BGR565LE,  ///< packed BGR 5:6:5, 16bpp, (msb)   5B 6G 5R(lsb), little-endian  AV_PIX_FMT_BGR555BE,  ///< packed BGR 5:5:5, 16bpp, (msb)1A 5B 5G 5R(lsb), big-endian, most significant bit to 1  AV_PIX_FMT_BGR555LE,  ///< packed BGR 5:5:5, 16bpp, (msb)1A 5B 5G 5R(lsb), little-endian, most significant bit to 1  AV_PIX_FMT_VAAPI_MOCO, ///< HW acceleration through VA API at motion compensation entry-point, Picture.data[3] contains a vaapi_render_state struct which contains macroblocks as well as various fields extracted from headers  AV_PIX_FMT_VAAPI_IDCT, ///< HW acceleration through VA API at IDCT entry-point, Picture.data[3] contains a vaapi_render_state struct which contains fields extracted from headers  AV_PIX_FMT_VAAPI_VLD,  ///< HW decoding through VA API, Picture.data[3] contains a vaapi_render_state struct which contains the bitstream of the slices as well as various fields extracted from headers  AV_PIX_FMT_YUV420P16LE,  ///< planar YUV 4:2:0, 24bpp, (1 Cr & Cb sample per 2x2 Y samples), little-endian  AV_PIX_FMT_YUV420P16BE,  ///< planar YUV 4:2:0, 24bpp, (1 Cr & Cb sample per 2x2 Y samples), big-endian  AV_PIX_FMT_YUV422P16LE,  ///< planar YUV 4:2:2, 32bpp, (1 Cr & Cb sample per 2x1 Y samples), little-endian  AV_PIX_FMT_YUV422P16BE,  ///< planar YUV 4:2:2, 32bpp, (1 Cr & Cb sample per 2x1 Y samples), big-endian  AV_PIX_FMT_YUV444P16LE,  ///< planar YUV 4:4:4, 48bpp, (1 Cr & Cb sample per 1x1 Y samples), little-endian  AV_PIX_FMT_YUV444P16BE,  ///< planar YUV 4:4:4, 48bpp, (1 Cr & Cb sample per 1x1 Y samples), big-endian#if FF_API_VDPAU  AV_PIX_FMT_VDPAU_MPEG4,  ///< MPEG4 HW decoding with VDPAU, data[0] contains a vdpau_render_state struct which contains the bitstream of the slices as well as various fields extracted from headers#endif  AV_PIX_FMT_DXVA2_VLD,///< HW decoding through DXVA2, Picture.data[3] contains a LPDIRECT3DSURFACE9 pointer  AV_PIX_FMT_RGB444LE,  ///< packed RGB 4:4:4, 16bpp, (msb)4A 4R 4G 4B(lsb), little-endian, most significant bits to 0  AV_PIX_FMT_RGB444BE,  ///< packed RGB 4:4:4, 16bpp, (msb)4A 4R 4G 4B(lsb), big-endian, most significant bits to 0  AV_PIX_FMT_BGR444LE,  ///< packed BGR 4:4:4, 16bpp, (msb)4A 4B 4G 4R(lsb), little-endian, most significant bits to 1  AV_PIX_FMT_BGR444BE,  ///< packed BGR 4:4:4, 16bpp, (msb)4A 4B 4G 4R(lsb), big-endian, most significant bits to 1  AV_PIX_FMT_GRAY8A,///< 8bit gray, 8bit alpha  AV_PIX_FMT_BGR48BE,   ///< packed RGB 16:16:16, 48bpp, 16B, 16G, 16R, the 2-byte value for each R/G/B component is stored as big-endian  AV_PIX_FMT_BGR48LE,   ///< packed RGB 16:16:16, 48bpp, 16B, 16G, 16R, the 2-byte value for each R/G/B component is stored as little-endian  /**   * The following 12 formats have the disadvantage of needing 1 format for each bit depth.   * Notice that each 9/10 bits sample is stored in 16 bits with extra padding.   * If you want to support multiple bit depths, then using AV_PIX_FMT_YUV420P16* with the bpp stored separately is better.   */  AV_PIX_FMT_YUV420P9BE, ///< planar YUV 4:2:0, 13.5bpp, (1 Cr & Cb sample per 2x2 Y samples), big-endian  AV_PIX_FMT_YUV420P9LE, ///< planar YUV 4:2:0, 13.5bpp, (1 Cr & Cb sample per 2x2 Y samples), little-endian  AV_PIX_FMT_YUV420P10BE,///< planar YUV 4:2:0, 15bpp, (1 Cr & Cb sample per 2x2 Y samples), big-endian  AV_PIX_FMT_YUV420P10LE,///< planar YUV 4:2:0, 15bpp, (1 Cr & Cb sample per 2x2 Y samples), little-endian  AV_PIX_FMT_YUV422P10BE,///< planar YUV 4:2:2, 20bpp, (1 Cr & Cb sample per 2x1 Y samples), big-endian  AV_PIX_FMT_YUV422P10LE,///< planar YUV 4:2:2, 20bpp, (1 Cr & Cb sample per 2x1 Y samples), little-endian  AV_PIX_FMT_YUV444P9BE, ///< planar YUV 4:4:4, 27bpp, (1 Cr & Cb sample per 1x1 Y samples), big-endian  AV_PIX_FMT_YUV444P9LE, ///< planar YUV 4:4:4, 27bpp, (1 Cr & Cb sample per 1x1 Y samples), little-endian  AV_PIX_FMT_YUV444P10BE,///< planar YUV 4:4:4, 30bpp, (1 Cr & Cb sample per 1x1 Y samples), big-endian  AV_PIX_FMT_YUV444P10LE,///< planar YUV 4:4:4, 30bpp, (1 Cr & Cb sample per 1x1 Y samples), little-endian  AV_PIX_FMT_YUV422P9BE, ///< planar YUV 4:2:2, 18bpp, (1 Cr & Cb sample per 2x1 Y samples), big-endian  AV_PIX_FMT_YUV422P9LE, ///< planar YUV 4:2:2, 18bpp, (1 Cr & Cb sample per 2x1 Y samples), little-endian  AV_PIX_FMT_VDA_VLD,///< hardware decoding through VDA#ifdef AV_PIX_FMT_ABI_GIT_MASTER  AV_PIX_FMT_RGBA64BE,  ///< packed RGBA 16:16:16:16, 64bpp, 16R, 16G, 16B, 16A, the 2-byte value for each R/G/B/A component is stored as big-endian  AV_PIX_FMT_RGBA64LE,  ///< packed RGBA 16:16:16:16, 64bpp, 16R, 16G, 16B, 16A, the 2-byte value for each R/G/B/A component is stored as little-endian  AV_PIX_FMT_BGRA64BE,  ///< packed RGBA 16:16:16:16, 64bpp, 16B, 16G, 16R, 16A, the 2-byte value for each R/G/B/A component is stored as big-endian  AV_PIX_FMT_BGRA64LE,  ///< packed RGBA 16:16:16:16, 64bpp, 16B, 16G, 16R, 16A, the 2-byte value for each R/G/B/A component is stored as little-endian#endif  AV_PIX_FMT_GBRP,  ///< planar GBR 4:4:4 24bpp  AV_PIX_FMT_GBRP9BE,   ///< planar GBR 4:4:4 27bpp, big-endian  AV_PIX_FMT_GBRP9LE,   ///< planar GBR 4:4:4 27bpp, little-endian  AV_PIX_FMT_GBRP10BE,  ///< planar GBR 4:4:4 30bpp, big-endian  AV_PIX_FMT_GBRP10LE,  ///< planar GBR 4:4:4 30bpp, little-endian  AV_PIX_FMT_GBRP16BE,  ///< planar GBR 4:4:4 48bpp, big-endian  AV_PIX_FMT_GBRP16LE,  ///< planar GBR 4:4:4 48bpp, little-endian  /**   * duplicated pixel formats for compatibility with libav.   * FFmpeg supports these formats since May 8 2012 and Jan 28 2012 (commits f9ca1ac7 and 143a5c55)   * Libav added them Oct 12 2012 with incompatible values (commit 6d5600e85)   */  AV_PIX_FMT_YUVA422P_LIBAV,  ///< planar YUV 4:2:2 24bpp, (1 Cr & Cb sample per 2x1 Y & A samples)  AV_PIX_FMT_YUVA444P_LIBAV,  ///< planar YUV 4:4:4 32bpp, (1 Cr & Cb sample per 1x1 Y & A samples)  AV_PIX_FMT_YUVA420P9BE,  ///< planar YUV 4:2:0 22.5bpp, (1 Cr & Cb sample per 2x2 Y & A samples), big-endian  AV_PIX_FMT_YUVA420P9LE,  ///< planar YUV 4:2:0 22.5bpp, (1 Cr & Cb sample per 2x2 Y & A samples), little-endian  AV_PIX_FMT_YUVA422P9BE,  ///< planar YUV 4:2:2 27bpp, (1 Cr & Cb sample per 2x1 Y & A samples), big-endian  AV_PIX_FMT_YUVA422P9LE,  ///< planar YUV 4:2:2 27bpp, (1 Cr & Cb sample per 2x1 Y & A samples), little-endian  AV_PIX_FMT_YUVA444P9BE,  ///< planar YUV 4:4:4 36bpp, (1 Cr & Cb sample per 1x1 Y & A samples), big-endian  AV_PIX_FMT_YUVA444P9LE,  ///< planar YUV 4:4:4 36bpp, (1 Cr & Cb sample per 1x1 Y & A samples), little-endian  AV_PIX_FMT_YUVA420P10BE, ///< planar YUV 4:2:0 25bpp, (1 Cr & Cb sample per 2x2 Y & A samples, big-endian)  AV_PIX_FMT_YUVA420P10LE, ///< planar YUV 4:2:0 25bpp, (1 Cr & Cb sample per 2x2 Y & A samples, little-endian)  AV_PIX_FMT_YUVA422P10BE, ///< planar YUV 4:2:2 30bpp, (1 Cr & Cb sample per 2x1 Y & A samples, big-endian)  AV_PIX_FMT_YUVA422P10LE, ///< planar YUV 4:2:2 30bpp, (1 Cr & Cb sample per 2x1 Y & A samples, little-endian)  AV_PIX_FMT_YUVA444P10BE, ///< planar YUV 4:4:4 40bpp, (1 Cr & Cb sample per 1x1 Y & A samples, big-endian)  AV_PIX_FMT_YUVA444P10LE, ///< planar YUV 4:4:4 40bpp, (1 Cr & Cb sample per 1x1 Y & A samples, little-endian)  AV_PIX_FMT_YUVA420P16BE, ///< planar YUV 4:2:0 40bpp, (1 Cr & Cb sample per 2x2 Y & A samples, big-endian)  AV_PIX_FMT_YUVA420P16LE, ///< planar YUV 4:2:0 40bpp, (1 Cr & Cb sample per 2x2 Y & A samples, little-endian)  AV_PIX_FMT_YUVA422P16BE, ///< planar YUV 4:2:2 48bpp, (1 Cr & Cb sample per 2x1 Y & A samples, big-endian)  AV_PIX_FMT_YUVA422P16LE, ///< planar YUV 4:2:2 48bpp, (1 Cr & Cb sample per 2x1 Y & A samples, little-endian)  AV_PIX_FMT_YUVA444P16BE, ///< planar YUV 4:4:4 64bpp, (1 Cr & Cb sample per 1x1 Y & A samples, big-endian)  AV_PIX_FMT_YUVA444P16LE, ///< planar YUV 4:4:4 64bpp, (1 Cr & Cb sample per 1x1 Y & A samples, little-endian)  AV_PIX_FMT_VDPAU, ///< HW acceleration through VDPAU, Picture.data[3] contains a VdpVideoSurface  AV_PIX_FMT_XYZ12LE,  ///< packed XYZ 4:4:4, 36 bpp, (msb) 12X, 12Y, 12Z (lsb), the 2-byte value for each X/Y/Z is stored as little-endian, the 4 lower bits are set to 0  AV_PIX_FMT_XYZ12BE,  ///< packed XYZ 4:4:4, 36 bpp, (msb) 12X, 12Y, 12Z (lsb), the 2-byte value for each X/Y/Z is stored as big-endian, the 4 lower bits are set to 0  AV_PIX_FMT_NV16, ///< interleaved chroma YUV 4:2:2, 16bpp, (1 Cr & Cb sample per 2x1 Y samples)  AV_PIX_FMT_NV20LE,   ///< interleaved chroma YUV 4:2:2, 20bpp, (1 Cr & Cb sample per 2x1 Y samples), little-endian  AV_PIX_FMT_NV20BE,   ///< interleaved chroma YUV 4:2:2, 20bpp, (1 Cr & Cb sample per 2x1 Y samples), big-endian  /**   * duplicated pixel formats for compatibility with libav.   * FFmpeg supports these formats since Sat Sep 24 06:01:45 2011 +0200 (commits 9569a3c9f41387a8c7d1ce97d8693520477a66c3)   * also see Fri Nov 25 01:38:21 2011 +0100 92afb431621c79155fcb7171d26f137eb1bee028   * Libav added them Sun Mar 16 23:05:47 2014 +0100 with incompatible values (commit 1481d24c3a0abf81e1d7a514547bd5305232be30)   */  AV_PIX_FMT_RGBA64BE_LIBAV, ///< packed RGBA 16:16:16:16, 64bpp, 16R, 16G, 16B, 16A, the 2-byte value for each R/G/B/A component is stored as big-endian  AV_PIX_FMT_RGBA64LE_LIBAV, ///< packed RGBA 16:16:16:16, 64bpp, 16R, 16G, 16B, 16A, the 2-byte value for each R/G/B/A component is stored as little-endian  AV_PIX_FMT_BGRA64BE_LIBAV, ///< packed RGBA 16:16:16:16, 64bpp, 16B, 16G, 16R, 16A, the 2-byte value for each R/G/B/A component is stored as big-endian  AV_PIX_FMT_BGRA64LE_LIBAV, ///< packed RGBA 16:16:16:16, 64bpp, 16B, 16G, 16R, 16A, the 2-byte value for each R/G/B/A component is stored as little-endian  AV_PIX_FMT_YVYU422,   ///< packed YUV 4:2:2, 16bpp, Y0 Cr Y1 Cb#ifndef AV_PIX_FMT_ABI_GIT_MASTER  AV_PIX_FMT_RGBA64BE=0x123,  ///< packed RGBA 16:16:16:16, 64bpp, 16R, 16G, 16B, 16A, the 2-byte value for each R/G/B/A component is stored as big-endian  AV_PIX_FMT_RGBA64LE,  ///< packed RGBA 16:16:16:16, 64bpp, 16R, 16G, 16B, 16A, the 2-byte value for each R/G/B/A component is stored as little-endian  AV_PIX_FMT_BGRA64BE,  ///< packed RGBA 16:16:16:16, 64bpp, 16B, 16G, 16R, 16A, the 2-byte value for each R/G/B/A component is stored as big-endian  AV_PIX_FMT_BGRA64LE,  ///< packed RGBA 16:16:16:16, 64bpp, 16B, 16G, 16R, 16A, the 2-byte value for each R/G/B/A component is stored as little-endian#endif  AV_PIX_FMT_0RGB=0x123+4,  ///< packed RGB 8:8:8, 32bpp, 0RGB0RGB...  AV_PIX_FMT_RGB0,  ///< packed RGB 8:8:8, 32bpp, RGB0RGB0...  AV_PIX_FMT_0BGR,  ///< packed BGR 8:8:8, 32bpp, 0BGR0BGR...  AV_PIX_FMT_BGR0,  ///< packed BGR 8:8:8, 32bpp, BGR0BGR0...  AV_PIX_FMT_YUVA444P,  ///< planar YUV 4:4:4 32bpp, (1 Cr & Cb sample per 1x1 Y & A samples)  AV_PIX_FMT_YUVA422P,  ///< planar YUV 4:2:2 24bpp, (1 Cr & Cb sample per 2x1 Y & A samples)  AV_PIX_FMT_YUV420P12BE, ///< planar YUV 4:2:0,18bpp, (1 Cr & Cb sample per 2x2 Y samples), big-endian  AV_PIX_FMT_YUV420P12LE, ///< planar YUV 4:2:0,18bpp, (1 Cr & Cb sample per 2x2 Y samples), little-endian  AV_PIX_FMT_YUV420P14BE, ///< planar YUV 4:2:0,21bpp, (1 Cr & Cb sample per 2x2 Y samples), big-endian  AV_PIX_FMT_YUV420P14LE, ///< planar YUV 4:2:0,21bpp, (1 Cr & Cb sample per 2x2 Y samples), little-endian  AV_PIX_FMT_YUV422P12BE, ///< planar YUV 4:2:2,24bpp, (1 Cr & Cb sample per 2x1 Y samples), big-endian  AV_PIX_FMT_YUV422P12LE, ///< planar YUV 4:2:2,24bpp, (1 Cr & Cb sample per 2x1 Y samples), little-endian  AV_PIX_FMT_YUV422P14BE, ///< planar YUV 4:2:2,28bpp, (1 Cr & Cb sample per 2x1 Y samples), big-endian  AV_PIX_FMT_YUV422P14LE, ///< planar YUV 4:2:2,28bpp, (1 Cr & Cb sample per 2x1 Y samples), little-endian  AV_PIX_FMT_YUV444P12BE, ///< planar YUV 4:4:4,36bpp, (1 Cr & Cb sample per 1x1 Y samples), big-endian  AV_PIX_FMT_YUV444P12LE, ///< planar YUV 4:4:4,36bpp, (1 Cr & Cb sample per 1x1 Y samples), little-endian  AV_PIX_FMT_YUV444P14BE, ///< planar YUV 4:4:4,42bpp, (1 Cr & Cb sample per 1x1 Y samples), big-endian  AV_PIX_FMT_YUV444P14LE, ///< planar YUV 4:4:4,42bpp, (1 Cr & Cb sample per 1x1 Y samples), little-endian  AV_PIX_FMT_GBRP12BE,///< planar GBR 4:4:4 36bpp, big-endian  AV_PIX_FMT_GBRP12LE,///< planar GBR 4:4:4 36bpp, little-endian  AV_PIX_FMT_GBRP14BE,///< planar GBR 4:4:4 42bpp, big-endian  AV_PIX_FMT_GBRP14LE,///< planar GBR 4:4:4 42bpp, little-endian  AV_PIX_FMT_GBRAP,   ///< planar GBRA 4:4:4:4 32bpp  AV_PIX_FMT_GBRAP16BE,   ///< planar GBRA 4:4:4:4 64bpp, big-endian  AV_PIX_FMT_GBRAP16LE,   ///< planar GBRA 4:4:4:4 64bpp, little-endian  AV_PIX_FMT_YUVJ411P,///< planar YUV 4:1:1, 12bpp, (1 Cr & Cb sample per 4x1 Y samples) full scale (JPEG), deprecated in favor of PIX_FMT_YUV411P and setting color_range  AV_PIX_FMT_BAYER_BGGR8,///< bayer, BGBG..(odd line), GRGR..(even line), 8-bit samples */  AV_PIX_FMT_BAYER_RGGB8,///< bayer, RGRG..(odd line), GBGB..(even line), 8-bit samples */  AV_PIX_FMT_BAYER_GBRG8,///< bayer, GBGB..(odd line), RGRG..(even line), 8-bit samples */  AV_PIX_FMT_BAYER_GRBG8,///< bayer, GRGR..(odd line), BGBG..(even line), 8-bit samples */  AV_PIX_FMT_BAYER_BGGR16LE, ///< bayer, BGBG..(odd line), GRGR..(even line), 16-bit samples, little-endian */  AV_PIX_FMT_BAYER_BGGR16BE, ///< bayer, BGBG..(odd line), GRGR..(even line), 16-bit samples, big-endian */  AV_PIX_FMT_BAYER_RGGB16LE, ///< bayer, RGRG..(odd line), GBGB..(even line), 16-bit samples, little-endian */  AV_PIX_FMT_BAYER_RGGB16BE, ///< bayer, RGRG..(odd line), GBGB..(even line), 16-bit samples, big-endian */  AV_PIX_FMT_BAYER_GBRG16LE, ///< bayer, GBGB..(odd line), RGRG..(even line), 16-bit samples, little-endian */  AV_PIX_FMT_BAYER_GBRG16BE, ///< bayer, GBGB..(odd line), RGRG..(even line), 16-bit samples, big-endian */  AV_PIX_FMT_BAYER_GRBG16LE, ///< bayer, GRGR..(odd line), BGBG..(even line), 16-bit samples, little-endian */  AV_PIX_FMT_BAYER_GRBG16BE, ///< bayer, GRGR..(odd line), BGBG..(even line), 16-bit samples, big-endian */#if !FF_API_XVMC  AV_PIX_FMT_XVMC,///< XVideo Motion Acceleration via common packet passing#endif /* !FF_API_XVMC */  AV_PIX_FMT_NB,///< number of pixel formats, DO NOT USE THIS if you want to link with shared libav* because the number of formats might differ between versions#if FF_API_PIX_FMT#include "old_pix_fmts.h"#endif};

FFmpeg有一个专门用于描述像素格式的结构体AVPixFmtDescriptor。该结构体的定义位于libavutil\pixdesc.h，如下所示。

/** * Descriptor that unambiguously describes how the bits of a pixel are * stored in the up to 4 data planes of an image. It also stores the * subsampling factors and number of components. * * @note This is separate of the colorspace (RGB, YCbCr, YPbPr, JPEG-style YUV *       and all the YUV variants) AVPixFmtDescriptor just stores how values *       are stored not what these values represent. */typedef struct AVPixFmtDescriptor{    const char *name;    uint8_t nb_components;      ///< The number of components each pixel has, (1-4)     /**     * Amount to shift the luma width right to find the chroma width.     * For YV12 this is 1 for example.     * chroma_width = -((-luma_width) >> log2_chroma_w)     * The note above is needed to ensure rounding up.     * This value only refers to the chroma components.     */    uint8_t log2_chroma_w;      ///< chroma_width = -((-luma_width )>>log2_chroma_w)     /**     * Amount to shift the luma height right to find the chroma height.     * For YV12 this is 1 for example.     * chroma_height= -((-luma_height) >> log2_chroma_h)     * The note above is needed to ensure rounding up.     * This value only refers to the chroma components.     */    uint8_t log2_chroma_h;    uint8_t flags;     /**     * Parameters that describe how pixels are packed.     * If the format has 2 or 4 components, then alpha is last.     * If the format has 1 or 2 components, then luma is 0.     * If the format has 3 or 4 components,     * if the RGB flag is set then 0 is red, 1 is green and 2 is blue;     * otherwise 0 is luma, 1 is chroma-U and 2 is chroma-V.     */    AVComponentDescriptor comp[4];}AVPixFmtDescriptor;

关于AVPixFmtDescriptor这个结构体不再做过多解释。它的定义比较简单，看注释就可以理解。通过av_pix_fmt_desc_get()可以获得指定像素格式的AVPixFmtDescriptor结构体。

/** * @return a pixel format descriptor for provided pixel format or NULL if * this pixel format is unknown. */const AVPixFmtDescriptor *av_pix_fmt_desc_get(enum AVPixelFormat pix_fmt);

通过AVPixFmtDescriptor结构体可以获得不同像素格式的一些信息。例如下文中用到了av_get_bits_per_pixel()，通过该函数可以获得指定像素格式每个像素占用的比特数（Bit Per Pixel）。

/** * Return the number of bits per pixel used by the pixel format * described by pixdesc. Note that this is not the same as the number * of bits per sample. * * The returned number of bits refers to the number of bits actually * used for storing the pixel information, that is padding bits are * not counted. */int av_get_bits_per_pixel(const AVPixFmtDescriptor *pixdesc);

其他的API在这里不做过多记录。

图像拉伸

FFmpeg支持多种像素拉伸的方式。这些方式的定义位于libswscale\swscale.h中，如下所示。

#define SWS_FAST_BILINEAR     1#define SWS_BILINEAR          2#define SWS_BICUBIC           4#define SWS_X                 8#define SWS_POINT          0x10#define SWS_AREA           0x20#define SWS_BICUBLIN       0x40#define SWS_GAUSS          0x80#define SWS_SINC          0x100#define SWS_LANCZOS       0x200#define SWS_SPLINE        0x400

其中SWS_BICUBIC性能比较好；SWS_FAST_BILINEAR在性能和速度之间有一个比好好的平衡，

而SWS_POINT的效果比较差。

有关这些方法的评测可以参考文章：

《ffmpeg中的sws_scale算法性能测试》

简单解释一下SWS_BICUBIC、SWS_BILINEAR和SWS_POINT的原理。

SWS_POINT（Nearest-neighbor interpolation， 邻域插值）

领域插值可以简单说成“1个点确定插值的点”。例如当图像放大后，新的样点根据距离它最近的样点的值取得自己的值。换句话说就是简单拷贝附近距离它最近的样点的值。领域插值是一种最基础的插值方法，速度最快，插值效果最不好，一般情况下不推荐使用。一般情况下使用邻域插值之后，画面会产生很多的“锯齿”。下图显示了4x4=16个彩色样点经过邻域插值后形成的图形。

SWS_BILINEAR（Bilinear interpolation， 双线性插值）

双线性插值可以简单说成“4个点确定插值的点”。它的计算过程可以简单用下图表示。图中绿色的P点是需要插值的点。首先通过Q11，Q21求得R1；Q12，Q22求得R2。然后根据R1，R2求得P。

其中求值的过程是一个简单的加权计算的过程。

设定Q11 = (x1, y1)，Q12 = (x1, y2)，Q21 = (x2, y1)，Q22 = (x2, y2)则各点的计算公式如下。

可以看出距离插值的点近一些的样点权值会大一些，远一些的样点权值要小一些。

下面看一个维基百科上的双线性插值的实例。该例子根据坐标为(20, 14)， (20, 15)， (21, 14)，(21, 15)的4个样点计算坐标为（20.2, 14.5）的插值点的值。

SWS_BICUBIC（Bicubic interpolation， 双三次插值）

双三次插值可以简单说成“16个点确定插值的点”。该插值算法比前两种算法复杂很多，插值后图像的质量也是最好的。有关它的插值方式比较复杂不再做过多记录。它的差值方法可以简单表述为下述公式。

其中aij的过程依赖于插值数据的特性。

维基百科上使用同样的样点进行邻域插值，双线性插值，双三次插值对比如下图所示。

Nearest-neighbor interpolation，邻域插值

Bilinear interpolation，双线性插值

Bicubic interpolation，双三次插值

YUV像素取值范围

FFmpeg中可以通过使用av_opt_set()设置“src_range”和“dst_range”来设置输入和输出的YUV的取值范围。如果“dst_range”字段设置为“1”的话，则代表输出的YUV的取值范围遵循“jpeg”标准；如果“dst_range”字段设置为“0”的话，则代表输出的YUV的取值范围遵循“mpeg”标准。下面记录一下YUV的取值范围的概念。

与RGB每个像素点的每个分量取值范围为0-255不同（每个分量占8bit），YUV取值范围有两种：

（1）       以Rec.601为代表（还包括BT.709 / BT.2020）的广播电视标准中，Y的取值范围是16-235，U、V的取值范围是16-240。FFmpeg中称之为“mpeg”范围。

（2）       以JPEG为代表的标准中，Y、U、V的取值范围都是0-255。FFmpeg中称之为“jpeg” 范围。

实际中最常见的是第1种取值范围的YUV（可以自己观察一下YUV的数据，会发现其中亮度分量没有取值为0、255这样的数值）。很多人在这个地方会有疑惑，为什么会去掉“两边”的取值呢？

在广播电视系统中不传输很低和很高的数值，实际上是为了防止信号变动造成过载，因而把这“两边”的数值作为“保护带”。下面这张图是数字电视中亮度信号量化后的电平分配图。从图中可以看出，对于8bit量化来说，信号的白电平为235，对应模拟电平为700mV；黑电平为16，对应模拟电平为0mV。信号上方的“保护带”取值范围是236至254，而信号下方的“保护带”取值范围是1-15。最边缘的0和255两个电平是保护电平，是不允许出现在数据流中的。与之类似，10bit量化的时候，白电平是235*4=940，黑电平是16*4=64。

下面两张图是数字电视中色度信号量化后的电平分配图。可以看出，色度最大正电平为240，对应模拟电平为+350mV；色度最大负电平为16，对应模拟电平为-350mV。需要注意的是，色度信号数字电平128对应的模拟电平是0mV。

色域

Libswscale支持色域的转换。有关色域的转换我目前还没有做太多的研究，仅记录一下目前最常见的三个标准中的色域：BT.601，BT.709，BT.2020。这三个标准中的色域逐渐增大。

在这里先简单解释一下CIE 1931颜色空间。这个空间围绕的区域像一个“舌头”，其中包含了自然界所有的颜色。CIE 1931颜色空间中的横坐标是x，纵坐标是y，x、y、z满足如下关系：

x + y + z = 1

“舌头”的边缘叫做“舌形曲线”，代表着饱和度为100%的光谱色。“舌头”的中心点（1/3，1/3）对应着白色，饱和度为0。

受显示器件性能的限制，电视屏幕是无法重现所有的颜色的，尤其是位于“舌形曲线”上的100% 饱和度的光谱色一般情况下是无法显示出来的。因此电视屏幕只能根据其具体的荧光粉的配方，有选择性的显示一部分的颜色，这部分可以显示的颜色称为色域。下文分别比较标清电视、高清电视和超高清电视标准中规定的色域。可以看出随着技术的进步，色域的范围正变得越来越大。

标清电视（SDTV）色域的规定源自于BT.601。高清电视（HDTV）色域的规定源自于BT.709。他们两个标准中的色域在CIE 1931颜色空间中的对比如下图所示。从图中可以看出，BT.709和BT.601色域差别不大，BT.709的色域要略微大于BT.601。

超高清电视（UHDTV）色域的规定源自于BT.2020。BT.2020和BT.709的色域在CIE 1931 颜色空间中的对比如下图所示。从图中可以看出，BT.2020的色域要远远大于BT.709。

从上面的对比也可以看出，对超高清电视（UHDTV）的显示器件的性能的要求更高了。这样超高清电视可以还原出一个更“真实”的世界。

下面这张图则使用实际的例子反映出色域范围大的重要性。图中的两个黑色三角形分别标识出了BT.709（小三角形）和BT.2020（大三角形）标准中的色域。从图中可以看出，如果使用色域较小的显示设备显示图片的话，将会损失掉很多的颜色。

源代码

本示例程序包含一个输入和一个输出，实现了从输入图像格式到输出图像格式之间的转换。

/** * 最简单的基于FFmpeg的Swscale示例 * Simplest FFmpeg Swscale * * 雷霄骅 Lei Xiaohua * [e-mail] * 中国传媒大学/数字电视技术 * Communication University of China / Digital TV Technology * http://blog.csdn.net/leixiaohua1020 * * 本程序使用libswscale对像素数据进行缩放转换等处理。 * 是最简单的libswscale的教程。 * * This software uses libswscale to scale / convert pixels. * It the simplest tutorial about libswscale. */#include <stdio.h>extern "C"{#include "libswscale/swscale.h"#include "libavutil/opt.h"#include "libavutil/imgutils.h"};int main(int argc, char* argv[]){  //Parameters   FILE *src_file =fopen("sintel_480x272_yuv420p.yuv", "rb");  const int src_w=480,src_h=272;  AVPixelFormat src_pixfmt=AV_PIX_FMT_YUV420P;  int src_bpp=av_get_bits_per_pixel(av_pix_fmt_desc_get(src_pixfmt));  FILE *dst_file = fopen("sintel_1280x720_rgb24.rgb", "wb");  const int dst_w=1280,dst_h=720;  AVPixelFormat dst_pixfmt=AV_PIX_FMT_RGB24;  int dst_bpp=av_get_bits_per_pixel(av_pix_fmt_desc_get(dst_pixfmt));  //Structures  uint8_t *src_data[4];  int src_linesize[4];  uint8_t *dst_data[4];  int dst_linesize[4];  int rescale_method=SWS_BICUBIC;  struct SwsContext *img_convert_ctx;  uint8_t *temp_buffer=(uint8_t *)malloc(src_w*src_h*src_bpp/8);  int frame_idx=0;  int ret=0;  ret= av_image_alloc(src_data, src_linesize,src_w, src_h, src_pixfmt, 1);  if (ret< 0) {     printf( "Could not allocate source image\n");     return -1;  }  ret = av_image_alloc(dst_data, dst_linesize,dst_w, dst_h, dst_pixfmt, 1);  if (ret< 0) {     printf( "Could not allocate destination image\n");     return -1;  }  //-----------------------------      //Init Method 1  img_convert_ctx =sws_alloc_context();  //Show AVOption  av_opt_show2(img_convert_ctx,stdout,AV_OPT_FLAG_VIDEO_PARAM,NULL);  //Set Value  av_opt_set_int(img_convert_ctx,"sws_flags",SWS_BICUBIC|SWS_PRINT_INFO,NULL);  av_opt_set_int(img_convert_ctx,"srcw",src_w,NULL);  av_opt_set_int(img_convert_ctx,"srch",src_h,NULL);  av_opt_set_int(img_convert_ctx,"src_format",src_pixfmt,NULL);  //'0' for MPEG (Y:0-235);'1' for JPEG (Y:0-255)  av_opt_set_int(img_convert_ctx,"src_range",1,NULL);  av_opt_set_int(img_convert_ctx,"dstw",dst_w,NULL);  av_opt_set_int(img_convert_ctx,"dsth",dst_h,NULL);  av_opt_set_int(img_convert_ctx,"dst_format",dst_pixfmt,NULL);  av_opt_set_int(img_convert_ctx,"dst_range",1,NULL);  sws_init_context(img_convert_ctx,NULL,NULL);  //Init Method 2  //img_convert_ctx = sws_getContext(src_w, src_h,src_pixfmt, dst_w, dst_h, dst_pixfmt,  //      rescale_method, NULL, NULL, NULL);  //-----------------------------  /*  //Colorspace  ret=sws_setColorspaceDetails(img_convert_ctx,sws_getCoefficients(SWS_CS_ITU601),0,     sws_getCoefficients(SWS_CS_ITU709),0,      0, 1 << 16, 1 << 16);  if (ret==-1) {     printf( "Colorspace not support.\n");     return -1;  }  */  while(1)  {     if (fread(temp_buffer, 1, src_w*src_h*src_bpp/8, src_file) != src_w*src_h*src_bpp/8){       break;     }     switch(src_pixfmt){     case AV_PIX_FMT_GRAY8:{       memcpy(src_data[0],temp_buffer,src_w*src_h);       break;                  }     case AV_PIX_FMT_YUV420P:{       memcpy(src_data[0],temp_buffer,src_w*src_h);  //Y       memcpy(src_data[1],temp_buffer+src_w*src_h,src_w*src_h/4);      //U       memcpy(src_data[2],temp_buffer+src_w*src_h*5/4,src_w*src_h/4);  //V       break;                   }     case AV_PIX_FMT_YUV422P:{       memcpy(src_data[0],temp_buffer,src_w*src_h);  //Y       memcpy(src_data[1],temp_buffer+src_w*src_h,src_w*src_h/2);      //U       memcpy(src_data[2],temp_buffer+src_w*src_h*3/2,src_w*src_h/2);  //V       break;                   }     case AV_PIX_FMT_YUV444P:{       memcpy(src_data[0],temp_buffer,src_w*src_h);  //Y       memcpy(src_data[1],temp_buffer+src_w*src_h,src_w*src_h);        //U       memcpy(src_data[2],temp_buffer+src_w*src_h*2,src_w*src_h);      //V       break;                   }     case AV_PIX_FMT_YUYV422:{       memcpy(src_data[0],temp_buffer,src_w*src_h*2);//Packed       break;                   }     case AV_PIX_FMT_RGB24:{       memcpy(src_data[0],temp_buffer,src_w*src_h*3);//Packed       break;                   }     default:{       printf("Not Support Input Pixel Format.\n");       break;                  }     }     sws_scale(img_convert_ctx, src_data, src_linesize, 0, src_h, dst_data, dst_linesize);     printf("Finish process frame %5d\n",frame_idx);     frame_idx++;     switch(dst_pixfmt){     case AV_PIX_FMT_GRAY8:{       fwrite(dst_data[0],1,dst_w*dst_h,dst_file);        break;                  }     case AV_PIX_FMT_YUV420P:{       fwrite(dst_data[0],1,dst_w*dst_h,dst_file);        //Y       fwrite(dst_data[1],1,dst_w*dst_h/4,dst_file);      //U       fwrite(dst_data[2],1,dst_w*dst_h/4,dst_file);      //V       break;                   }     case AV_PIX_FMT_YUV422P:{       fwrite(dst_data[0],1,dst_w*dst_h,dst_file);   //Y       fwrite(dst_data[1],1,dst_w*dst_h/2,dst_file);        //U       fwrite(dst_data[2],1,dst_w*dst_h/2,dst_file);        //V       break;                   }     case AV_PIX_FMT_YUV444P:{       fwrite(dst_data[0],1,dst_w*dst_h,dst_file);        //Y       fwrite(dst_data[1],1,dst_w*dst_h,dst_file);        //U       fwrite(dst_data[2],1,dst_w*dst_h,dst_file);        //V       break;                   }     case AV_PIX_FMT_YUYV422:{       fwrite(dst_data[0],1,dst_w*dst_h*2,dst_file);      //Packed       break;                   }     case AV_PIX_FMT_RGB24:{       fwrite(dst_data[0],1,dst_w*dst_h*3,dst_file);      //Packed       break;                  }     default:{       printf("Not Support Output Pixel Format.\n");       break;                }     }  }  sws_freeContext(img_convert_ctx);  free(temp_buffer);  fclose(dst_file);  av_freep(&src_data[0]);  av_freep(&dst_data[0]);  return 0;}

运行结果

程序的输入为一个名称为“sintel_480x272_yuv420p.yuv”的视频。该视频像素格式是YUV420P，分辨率为480x272。

程序的输出为一个名称为“sintel_1280x720_rgb24.rgb”的视频。该视频像素格式是RGB24，分辨率为1280x720。

下载

Simplest FFmpeg Swscale

SourceForge项目主页：https://sourceforge.net/projects/simplestffmpegswscale/

CDSN下载地址： http://download.csdn.net/detail/leixiaohua1020/8292175

本教程是最简单的基于FFmpeg的libswscale进行像素处理的教程。它包含了两个工程：

simplest_ffmpeg_swscale: 最简单的libswscale的教程。

simplest_pic_gen: 生成各种测试图片的工具。

http://www.tuicool.com/articles/UzIBbai