深入浅出FFMPEG（一） SDK version 0.1

深入浅出FFMPEG

数字媒体处理的基本流程

认识FFMPEG

FFMPEG堪称自由软件中最完备的一套多媒体支持库，它几乎实现了所有当下常见的数据封装格式、多媒体传输协议以及音视频编解码器。因此，对于从事多媒体技术开发的工程师来说，深入研究FFMPEG成为一门必不可少的工作，可以这样说，FFMPEG之于多媒体开发工程师的重要性正如kernel之于嵌入式系统工程师一般。

几个小知识：

• FFMPEG项目是由法国人Fabrice Bellard发起的，此人也是著名的CPU模拟器项目QEMU的发起者，同时还是圆周率算法纪录的保持者。
• FF是Fast Forward的意思，翻译成中文是“快进”。
• FFMPEG的LOGO是一个”Z字扫描”示意图，Z字扫描用于将图像的二维频域数据一维化，同时保证了一维化的数据具备良好的统计特性，从而提高其后要进行的一维熵编码的效率。

关于耻辱柱（Hall of Shame）：FFMpeg大部分代码遵循LGPL许可证，如果使用者对FFMpeg进行了修改，要求公布修改的源代码；有少部分代码遵循GPL许可证，要求使用者同时公开使用FFMpeg的软件的源代码。实际上，除去部分大的系统软件开发商（Microsoft、Apple等）以及某些著名的音视频服务提供商（Divx、Real等）提供的自有播放器之外，绝大部分第三方开发的播放器都离不开FFMpeg的支持，像Linux桌面环境中的开源播放器VLC、MPlayer，Windows下的KMPlayer、暴风影音以及Android下几乎全部第三方播放器都是基于FFMpeg的。也有许多看似具备自主技术的播放器，其实也都不声不响地使用了FFMpeg，这种行为被称为“盗窃”，参与“盗窃”的公司的名字则被刻在耻辱柱上，国产播放器暴风影音、QQ影音于2009年上榜。

一个简单的测试程序

#include <stdio.h>#include <string.h>#include <stdlib.h> #include <sys/time.h> #include "libavutil/avstring.h"#include "libavformat/avformat.h"#include "libavdevice/avdevice.h"#include "libavcodec/opt.h"#include "libswscale/swscale.h" #define DECODED_AUDIO_BUFFER_SIZE            192000 struct options{    int streamId;    int frames;    int nodec;    int bplay;    int thread_count;    int64_t lstart;    char finput[256];    char foutput1[256];    char foutput2[256];}; int parse_options(struct options *opts, int argc, char** argv){    int optidx;    char *optstr;     if (argc < 2) return -1;     opts->streamId = -1;    opts->lstart = -1;    opts->frames = -1;    opts->foutput1[0] = 0;    opts->foutput2[0] = 0;    opts->nodec = 0;    opts->bplay = 0;    opts->thread_count = 0;    strcpy(opts->finput, argv[1]);     optidx = 2;    while (optidx < argc)    {        optstr = argv[optidx++];        if (*optstr++ != '-') return -1;        switch (*optstr++)        {        case 's':  //< stream id            opts->streamId = atoi(optstr);            break;        case 'f':  //< frames            opts->frames = atoi(optstr);            break;        case 'k':  //< skipped            opts->lstart = atoll(optstr);            break;        case 'o':  //< output            strcpy(opts->foutput1, optstr);            strcat(opts->foutput1, ".mpg");            strcpy(opts->foutput2, optstr);            strcat(opts->foutput2, ".raw");            break;        case 'n': //decoding and output options            if (strcmp("dec", optstr) == 0)                opts->nodec = 1;            break;        case 'p':            opts->bplay = 1;            break;        case 't':            opts->thread_count = atoi(optstr);            break;        default:            return -1;        }    }     return 0;} void show_help(char* program){    printf("Simple FFMPEG test program\n");    printf("Usage: %s inputfile [-sstreamid [-fframes] [-kskipped] [-ooutput_filename(without extension)] [-p] [-tthread_count]]\n",            program);    return;} static void log_callback(void* ptr, int level, const char* fmt, va_list vl){    vfprintf(stdout, fmt, vl);} #include <sys/ioctl.h>#include <unistd.h>#include <fcntl.h>#include <sys/soundcard.h> #define OSS_DEVICE "/dev/dsp0" struct audio_dsp{    int audio_fd;    int channels;    int format;    int speed;};int map_formats(enum SampleFormat format){    switch(format)    {        case SAMPLE_FMT_U8:            return AFMT_U8;        case SAMPLE_FMT_S16:            return AFMT_S16_LE;        default:            return AFMT_U8;     }}int set_audio(struct audio_dsp* dsp){    if (dsp->audio_fd == -1)    {        printf("Invalid audio dsp id!\n");        return -1;    }         if (-1 == ioctl(dsp->audio_fd, SNDCTL_DSP_SETFMT, &dsp->format))    {        printf("Failed to set dsp format!\n");        return -1;    }     if (-1 == ioctl(dsp->audio_fd, SNDCTL_DSP_CHANNELS, &dsp->channels))    {        printf("Failed to set dsp format!\n");        return -1;    }     if (-1 == ioctl(dsp->audio_fd, SNDCTL_DSP_SPEED, &dsp->speed))    {        printf("Failed to set dsp format!\n");        return -1;    }        return 0;} int play_pcm(struct audio_dsp* dsp, unsigned char *buf, int size){    if (dsp->audio_fd == -1)    {        printf("Invalid audio dsp id!\n");        return -1;    }     if (-1 == write(dsp->audio_fd, buf, size))    {        printf("Failed to write audio dsp!\n");        return -1;    }     return 0;} #include <linux/fb.h>#include <sys/mman.h> #define FB_DEVICE "/dev/fb0" enum pic_format{    eYUV_420_Planer,};struct video_fb{    int video_fd;    struct fb_var_screeninfo vinfo;    struct fb_fix_screeninfo finfo;    unsigned char *fbp;    AVFrame *frameRGB;    struct     {        int x;        int y;    } video_pos;}; int open_video(struct video_fb *fb, int x, int y){    int screensize;    fb->video_fd = open(FB_DEVICE, O_WRONLY);    if (fb->video_fd == -1) return -1;     if (ioctl(fb->video_fd, FBIOGET_FSCREENINFO, &fb->finfo)) return -2;    if (ioctl(fb->video_fd, FBIOGET_VSCREENINFO, &fb->vinfo)) return -2;      printf("video device: resolution %dx%d, �pp\n", fb->vinfo.xres, fb->vinfo.yres, fb->vinfo.bits_per_pixel);    screensize = fb->vinfo.xres * fb->vinfo.yres * fb->vinfo.bits_per_pixel / 8;    fb->fbp = (unsigned char *) mmap(0, screensize, PROT_READ|PROT_WRITE, MAP_SHARED, fb->video_fd, 0);    if (fb->fbp == -1) return -3;     if (x >= fb->vinfo.xres || y >= fb->vinfo.yres)    {        return -4;    }    else    {        fb->video_pos.x = x;        fb->video_pos.y = y;    }     fb->frameRGB = avcodec_alloc_frame();    if (!fb->frameRGB) return -5;     return 0;}#if 0int show_picture(struct video_fb *fb, AVFrame *frame, int width, int height, enum pic_format format){    struct SwsContext *sws;    int i;    unsigned char *dest;    unsigned char *src;     if (fb->video_fd == -1) return -1;    if ((fb->video_pos.x >= fb->vinfo.xres) || (fb->video_pos.y >= fb->vinfo.yres)) return -2;     if (fb->video_pos.x + width > fb->vinfo.xres)    {        width = fb->vinfo.xres - fb->video_pos.x;    }    if (fb->video_pos.y + height > fb->vinfo.yres)    {        height = fb->vinfo.yres - fb->video_pos.y;    }     if (format == PIX_FMT_YUV420P)    {        sws = sws_getContext(width, height, format, width, height, PIX_FMT_RGB32, SWS_FAST_BILINEAR, NULL, NULL, NULL);        if (sws == 0)        {            return -3;        }        if (sws_scale(sws, frame->data, frame->linesize, 0, height, fb->frameRGB->data, fb->frameRGB->linesize))        {            return -3;        }         dest = fb->fbp + (fb->video_pos.x+fb->vinfo.xoffset) * (fb->vinfo.bits_per_pixel/8) +(fb->video_pos.y+fb->vinfo.yoffset) * fb->finfo.line_length;        for (i = 0; i < height; i++)        {            memcpy(dest, src, width*4);            src += fb->frameRGB->linesize[0];            dest += fb->finfo.line_length;        }    }    return 0;}#endifvoid close_video(struct video_fb *fb){    if (fb->video_fd != -1)     {        munmap(fb->fbp, fb->vinfo.xres * fb->vinfo.yres * fb->vinfo.bits_per_pixel / 8);        close(fb->video_fd);        fb->video_fd = -1;    }} int main(int argc, char **argv){    AVFormatContext* pCtx = 0;    AVCodecContext *pCodecCtx = 0;    AVCodec *pCodec = 0;    AVPacket packet;    AVFrame *pFrame = 0;    FILE *fpo1 = NULL;    FILE *fpo2 = NULL;    int nframe;    int err;    int got_picture;    int picwidth, picheight, linesize;    unsigned char *pBuf;    int i;    int64_t timestamp;    struct options opt;    int usefo = 0;    struct audio_dsp dsp;    int dusecs;    float usecs1 = 0;    float usecs2 = 0;    struct timeval elapsed1, elapsed2;    int decoded = 0;     av_register_all();     av_log_set_callback(log_callback);    av_log_set_level(50);     if (parse_options(&opt, argc, argv) < 0 || (strlen(opt.finput) == 0))    {        show_help(argv[0]);        return 0;    }      err = avformat_open_input(&pCtx, opt.finput, 0, 0);    if (err < 0)    {        printf("\n->(avformat_open_input)\tERROR:\t%d\n", err);        goto fail;    }    err = avformat_find_stream_info(pCtx, 0);    if (err < 0)    {        printf("\n->(avformat_find_stream_info)\tERROR:\t%d\n", err);        goto fail;    }    if (opt.streamId < 0)    {        av_dump_format(pCtx, 0, pCtx->filename, 0);        goto fail;    }    else    {        printf("\n extra data in Stream %d (�):", opt.streamId, pCtx->streams[opt.streamId]->codec->extradata_size);        for (i = 0; i < pCtx->streams[opt.streamId]->codec->extradata_size; i++)        {            if (i%16 == 0) printf("\n");            printf("%2x  ", pCtx->streams[opt.streamId]->codec->extradata[i]);        }    }        if (strlen(opt.foutput1) && strlen(opt.foutput2))    {        fpo1 = fopen(opt.foutput1, "wb");        fpo2 = fopen(opt.foutput2, "wb");        if (!fpo1 || !fpo2)        {            printf("\n->error opening output files\n");            goto fail;        }        usefo = 1;    }    else    {        usefo = 0;    }     if (opt.streamId >= pCtx->nb_streams)    {        printf("\n->StreamId\tERROR\n");        goto fail;    }     if (opt.lstart > 0)    {        err = av_seek_frame(pCtx, opt.streamId, opt.lstart, AVSEEK_FLAG_ANY);        if (err < 0)        {            printf("\n->(av_seek_frame)\tERROR:\t%d\n", err);            goto fail;        }    }         if (!opt.nodec)    {                pCodecCtx = pCtx->streams[opt.streamId]->codec;         if (opt.thread_count <= 16 && opt.thread_count > 0 )        {            pCodecCtx->thread_count = opt.thread_count;            pCodecCtx->thread_type = FF_THREAD_FRAME;        }        pCodec = avcodec_find_decoder(pCodecCtx->codec_id);        if (!pCodec)        {            printf("\n->can not find codec!\n");            goto fail;        }        err = avcodec_open2(pCodecCtx, pCodec, 0);        if (err < 0)        {            printf("\n->(avcodec_open)\tERROR:\t%d\n", err);            goto fail;        }        pFrame = avcodec_alloc_frame();                         if (opt.bplay)        {                        dsp.audio_fd = open(OSS_DEVICE, O_WRONLY);            if (dsp.audio_fd == -1)            {                printf("\n-> can not open audio device\n");                goto fail;            }            dsp.channels = pCodecCtx->channels;            dsp.speed = pCodecCtx->sample_rate;            dsp.format = map_formats(pCodecCtx->sample_fmt);            if (set_audio(&dsp) < 0)            {                printf("\n-> can not set audio device\n");                goto fail;            }                    }    }     nframe = 0;    while(nframe < opt.frames || opt.frames == -1)    {        gettimeofday(&elapsed1, NULL);        err = av_read_frame(pCtx, &packet);        if (err < 0)        {            printf("\n->(av_read_frame)\tERROR:\t%d\n", err);            break;        }        gettimeofday(&elapsed2, NULL);        dusecs = (elapsed2.tv_sec - elapsed1.tv_sec)*1000000 + (elapsed2.tv_usec - elapsed1.tv_usec);        usecs2 += dusecs;                timestamp = av_rescale_q(packet.dts, pCtx->streams[packet.stream_index]->time_base, (AVRational){1, AV_TIME_BASE});        printf("\nFrame No ] stream#%d\tsize mB, timestamp:%6lld, dts:%6lld, pts:%6lld, ", nframe++, packet.stream_index, packet.size,                timestamp, packet.dts, packet.pts);         if (packet.stream_index == opt.streamId)        {#if 0             for (i = 0; i < 16;  i++)            {                if (i%16 == 0) printf("\n pktdata: ");                printf("%2x  ", packet.data[i]);            }            printf("\n");#endif                        if (usefo)            {                fwrite(packet.data, packet.size, 1, fpo1);                fflush(fpo1);            }             if (pCtx->streams[opt.streamId]->codec->codec_type == AVMEDIA_TYPE_VIDEO && !opt.nodec)            {                picheight = pCtx->streams[opt.streamId]->codec->height;                picwidth = pCtx->streams[opt.streamId]->codec->width;                 gettimeofday(&elapsed1, NULL);                 avcodec_decode_video2(pCodecCtx, pFrame, &got_picture, &packet);                decoded++;                gettimeofday(&elapsed2, NULL);                dusecs = (elapsed2.tv_sec - elapsed1.tv_sec)*1000000 + (elapsed2.tv_usec - elapsed1.tv_usec);                usecs1 += dusecs;                 if (got_picture)                {                    printf("[Video: type %d, ref %d, pts %lld, pkt_pts %lld, pkt_dts %lld]",                             pFrame->pict_type, pFrame->reference, pFrame->pts, pFrame->pkt_pts, pFrame->pkt_dts);                     if (pCtx->streams[opt.streamId]->codec->pix_fmt == PIX_FMT_YUV420P)                    {                        if (usefo)                        {                            linesize = pFrame->linesize[0];                            pBuf = pFrame->data[0];                            for (i = 0; i < picheight; i++)                            {                                fwrite(pBuf, picwidth, 1, fpo2);                                pBuf += linesize;                            }                             linesize = pFrame->linesize[1];                            pBuf = pFrame->data[1];                            for (i = 0; i < picheight/2; i++)                            {                                fwrite(pBuf, picwidth/2, 1, fpo2);                                pBuf += linesize;                            }                                        linesize = pFrame->linesize[2];                            pBuf = pFrame->data[2];                            for (i = 0; i < picheight/2; i++)                            {                                fwrite(pBuf, picwidth/2, 1, fpo2);                                pBuf += linesize;                            }                              fflush(fpo2);                        }                          if (opt.bplay)                        {                                                    }                    }                }                av_free_packet(&packet);            }            else if (pCtx->streams[opt.streamId]->codec->codec_type == AVMEDIA_TYPE_AUDIO && !opt.nodec)            {                int got;                 gettimeofday(&elapsed1, NULL);                avcodec_decode_audio4(pCodecCtx, pFrame, &got, &packet);                decoded++;                gettimeofday(&elapsed2, NULL);                dusecs = (elapsed2.tv_sec - elapsed1.tv_sec)*1000000 + (elapsed2.tv_usec - elapsed1.tv_usec);                usecs1 += dusecs;                                 if (got)                                {                    printf("[Audio: ]B raw data, decoding time: %d]", pFrame->linesize[0], dusecs);                    if (usefo)                    {                        fwrite(pFrame->data[0],  pFrame->linesize[0], 1, fpo2);                        fflush(fpo2);                    }                    if (opt.bplay)                    {                        play_pcm(&dsp, pFrame->data[0],  pFrame->linesize[0]);                    }                                }            }        }    }       if (!opt.nodec && pCodecCtx)    {        avcodec_close(pCodecCtx);    }     printf("\n%d frames parsed, average %.2f us per frame\n", nframe, usecs2/nframe);    printf("%d frames decoded, average %.2f us per frame\n", decoded, usecs1/decoded); fail:    if (pCtx)    {        avformat_close_input(&pCtx);    }    if (fpo1)    {        fclose(fpo1);    }    if (fpo2)    {        fclose(fpo2);    }    if (!pFrame)    {        av_free(pFrame);    }    if (!usefo && (dsp.audio_fd != -1))    {        close(dsp.audio_fd);    }    return 0;}

这一小段代码可以实现的功能包括：

• 打开一个多媒体文件并获取基本的媒体信息。
• 获取编码器句柄。
• 根据给定的时间标签进行一个跳转。
• 读取数据帧。
• 解码音频帧或者视频帧。
• 关闭多媒体文件。

这些功能足以支持一个功能强大的多媒体播放器，因为最复杂的解复用、解码、数据分析过程已经在FFMpeg内部实现了，需要关注的仅剩同步问题。