深入浅出FFMPEG（一） SDK version 0.11
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：
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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。
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FF是Fast Forward的意思，翻译成中文是“快进”。
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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 0 int 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; } #endif void 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：
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打开一个多媒体文件并获取基本的媒体信息。
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获取编码器句柄。
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根据给定的时间标签进行一个跳转。
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读取数据帧。
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解码音频帧或者视频帧。
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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。