ffmpeg-tutorial04分析.doc

在阅读ffmpeg-tutorial代码的时候，参阅了网上的一分ffmpeg-tutorial分析中文版，在此基础上理解这几分代码的原理，下面是我对tutorial04框架的梳理。/*从main()进入int main(int argc, char *argv) SDL_Event event;VideoState *is;is = av_mallocz(sizeof(VideoState);if(argc 2) fprintf(stderr, Usage: test n);exit(1);/ Register all formats and codecsav_register_all();if(SDL_Init(SDL_INIT_VIDEO | SDL_INIT_AUDIO | SDL_INIT_TIMER) fprintf(stderr, Could not initialize SDL - %sn, SDL_GetError();exit(1);/ Make a screen to put our video#ifndef _DARWIN_screen = SDL_SetVideoMode(640, 480, 0, 0);#elsescreen = SDL_SetVideoMode(640, 480, 24, 0);#endifif(!screen) fprintf(stderr, SDL: could not set video mode - exitingn);exit(1);av_strlcpy(is-filename,argv1, sizeof(is-filename);is-pictq_mutex = SDL_CreateMutex();is-pictq_cond = SDL_CreateCond();printf(main 1n);/设置定时器，播放第一帧画面。schedule_refresh(is, 40);is-parse_tid = SDL_CreateThread(decode_thread, is);if(!is-parse_tid) av_free(is);return -1;for(;) 省略一些代码/*进入decode_thread前面都是一些基础的操作。int decode_thread(void *arg) VideoState *is = (VideoState *)arg;AVFormatContext *pFormatCtx;AVPacket pkt1, *packet = &pkt1;int video_index = -1;int audio_index = -1;int i;is-videoStream=-1;is-audioStream=-1;global_video_state = is;/ will interrupt blocking functions if we quit!url_set_interrupt_cb(decode_interrupt_cb);/ Open video fileif(av_open_input_file(&pFormatCtx, is-filename, NULL, 0, NULL)!=0)return -1; / Couldnt open fileis-pFormatCtx = pFormatCtx;/ Retrieve stream informationif(av_find_stream_info(pFormatCtx)filename, 0);/ Find the first video streamfor(i=0; inb_streams; i+) if(pFormatCtx-streamsi-codec-codec_type=CODEC_TYPE_VIDEO &video_index streamsi-codec-codec_type=CODEC_TYPE_AUDIO &audio_index = 0) stream_component_open(is, audio_index);if(video_index = 0) stream_component_open(is, video_index); if(is-videoStream audioStream filename);goto fail;/ main decode loopprintf(decode_thread 1n);for(;) if(is-quit) break;/ seek stuff goes hereif(is-audioq.size MAX_AUDIOQ_SIZE |is-videoq.size MAX_VIDEOQ_SIZE) SDL_Delay(10);continue;if(av_read_frame(is-pFormatCtx, packet) pb) = 0) SDL_Delay(100); /* no error; wait for user input */continue; else break;printf(decode_thread 2n);/ Is this a packet from the video stream?if(packet-stream_index = is-videoStream) packet_queue_put(&is-videoq, packet); else if(packet-stream_index = is-audioStream) packet_queue_put(&is-audioq, packet); else av_free_packet(packet);/* all done - wait for it */while(!is-quit) SDL_Delay(100);fail:printf(decode_thread 3n);if(1)SDL_Event event;event.type = FF_QUIT_EVENT;event.user.data1 = is;SDL_PushEvent(&event);return 0;decode_thread里打开音频流和视频流，然后进入for循环，不断读入packet，并将video和audio的packet分别存入is-videoq和is-audioq，这里来看一下打开视频流和音频流函数。/*int stream_component_open(VideoState *is, int stream_index) AVFormatContext *pFormatCtx = is-pFormatCtx;AVCodecContext *codecCtx;AVCodec *codec;SDL_AudioSpec wanted_spec, spec;if(stream_index = pFormatCtx-nb_streams) return -1;/ Get a pointer to the codec context for the video streamcodecCtx = pFormatCtx-streamsstream_index-codec;if(codecCtx-codec_type = CODEC_TYPE_AUDIO) / Set audio settings from codec infowanted_spec.freq = codecCtx-sample_rate;wanted_spec.format = AUDIO_S16SYS;wanted_spec.channels = codecCtx-channels;wanted_spec.silence = 0;wanted_spec.samples = SDL_AUDIO_BUFFER_SIZE;wanted_spec.callback = audio_callback;wanted_spec.userdata = is;if(SDL_OpenAudio(&wanted_spec, &spec) codec_id);if(!codec | (avcodec_open(codecCtx, codec) codec_type) case CODEC_TYPE_AUDIO:is-audioStream = stream_index;is-audio_st = pFormatCtx-streamsstream_index;is-audio_buf_size = 0;is-audio_buf_index = 0;memset(&is-audio_pkt, 0, sizeof(is-audio_pkt);packet_queue_init(&is-audioq);SDL_PauseAudio(0);break;case CODEC_TYPE_VIDEO:is-videoStream = stream_index;is-video_st = pFormatCtx-streamsstream_index;packet_queue_init(&is-videoq);is-video_tid = SDL_CreateThread(video_thread, is);break;default:break;如果是video，则进入video_thread，如果是audio，则进入audio_callback，这里我们来看一下video_thread，audio_callback和tutorial03是一样的。/*int video_thread(void *arg) VideoState *is = (VideoState *)arg;AVPacket pkt1, *packet = &pkt1;int len1, frameFinished;AVFrame *pFrame;pFrame = avcodec_alloc_frame();for(;) if(packet_queue_get(&is-videoq, packet, 1) video_st-codec, pFrame, &frameFinished, packet-data, packet-size);/ Did we get a video frame?if(frameFinished) if(queue_picture(is, pFrame) videoq中取邮video packet，然后调用avcodec_decode_video解码出pFrame，之后调用queue_picture将解码出的一帧图像存入videopicturetypedef struct VideoPicture SDL_Overlay *bmp;int width, height; /* source height & width */int allocated; VideoPicture;VideoPicture结构体是一个SDL_Overlay集合，每一帧图像保存在一个Overlay中，显示的时候直接覆盖。来看看queue_picture/*/int queue_picture(VideoState *is, AVFrame *pFrame) VideoPicture *vp;int dst_pix_fmt;AVPicture pict;struct SwsContext *ctx;/* wait until we have space for a new pic */SDL_LockMutex(is-pictq_mutex);while(is-pictq_size = VIDEO_PICTURE_QUEUE_SIZE &!is-quit) SDL_CondWait(is-pictq_cond, is-pictq_mutex);SDL_UnlockMutex(is-pictq_mutex);if(is-quit)return -1;/ windex is set to 0 initiallyvp = &is-pictqis-pictq_windex;/* allocate or resize the buffer! */如果vp-bmp还没有创建，则发送FF_ALLOC_EVENT创建if(!vp-bmp |vp-width != is-video_st-codec-width |vp-height != is-video_st-codec-height) SDL_Event event;vp-allocated = 0;/* we have to do it in the main thread */event.type = FF_ALLOC_EVENT;event.user.data1 = is;SDL_PushEvent(&event);/* wait until we have a picture allocated */SDL_LockMutex(is-pictq_mutex);while(!vp-allocated & !is-quit) SDL_CondWait(is-pictq_cond, is-pictq_mutex);SDL_UnlockMutex(is-pictq_mutex);if(is-quit) return -1;/* We have a place to put our picture on the queue */ctx = sws_getContext(is-video_st-codec-width, is-video_st-codec-height,is-video_st-codec-pix_fmt,is-video_st-codec-width, is-video_st-codec-height,PIX_FMT_YUV420P,SWS_BICUBIC, NULL, NULL, NULL);if(vp-bmp) SDL_LockYUVOverlay(vp-bmp);/写入数据到SDL_Overlay中dst_pix_fmt = PIX_FMT_YUV420P;/* point pict at the queue */pict.data0 = vp-bmp-pixels0;pict.data1 = vp-bmp-pixels2;pict.data2 = vp-bmp-pixels1;pict.linesize0 = vp-bmp-pitches0;pict.linesize1 = vp-bmp-pitches2;pict.linesize2 = vp-bmp-pitches1;/ Convert the image into YUV format that SDL uses/img_convert(&pict, dst_pix_fmt,/(AVPicture *)pFrame, is-video_st-codec-pix_fmt, /is-video_st-codec-width, is-video_st-codec-height);sws_scale(ctx, pFrame-data, pFrame-linesize, 0, is-video_st-codec-height,pict.data, pict.linesize);SDL_UnlockYUVOverlay(vp-bmp);/* now we inform our display thread that we have a pic ready */if(+is-pictq_windex = VIDEO_PICTURE_QUEUE_SIZE) is-pictq_windex = 0;SDL_LockMutex(is-pictq_mutex);is-pictq_size+;SDL_UnlockMutex(is-pictq_mutex);return 0;这里发送了一个FF_ALLOC_EVENT消息，在main函数中截获这个消息后调用my_alloc_picture创建一个SDL_Overlayvoid my_alloc_picture(void *userdata) VideoState *is = (VideoState *)userdata;VideoPicture *vp;vp = &is-pictqis-pictq_windex;if(vp-bmp) / we already have one make another, bigger/smallerSDL_FreeYUVOverlay(vp-bmp);/ Allocate a place to put our YUV image on that screenvp-bmp = SDL_CreateYUVOverlay(is-video_st-codec-width,is-video_st-codec-height,SDL_YV12_OVERLAY,screen);vp-width = is-video_st-codec-width;vp-height = is-video_st-codec-height;SDL_LockMutex(is-pictq_mutex);vp-allocated = 1;SDL_CondSignal(is-pictq_cond);SDL_UnlockMutex(is-pictq_mutex);我们回过头来看看main函数/*int main(int argc, char *argv) schedule_refresh(is, 40);for(;) printf(main 2n);SDL_WaitEvent(&event);switch(event.type) case FF_QUIT_EVENT:case SDL_QUIT:is-quit = 1;SDL_Quit();return 0;break;case FF_ALLOC_EVENT:my_alloc_picture(event.user.data1);break;case FF_REFRESH_EVENT:video_refresh_timer(event.user.data1);break;default:break;一开始进入main时就调用了schedule_refresh(is, 40);/*static void schedule_refresh(VideoState *is, int delay) printf(schedule_refreshn);SDL_AddTimer(delay, sdl_refresh_timer_cb, is);/*static Uint32 sdl_refresh_timer_cb(Uint32 interval, void *opaque) SDL_Event event;event.type = FF_REFRESH_EVENT;event.user.data1 = opaque;SDL_PushEvent(&event);printf(sdl_refresh_timer_cbn);return 0; /* 0 means stop timer */我们可以看到，调用schedule_refresh- sdl_refresh_timer_cb发送FF_REFRESH_EVENT显示一个SDL_Overlay，即显示一幅图像。/*void video_refresh_timer(void *userdata) VideoState *is = (V