Tutorial 04: Spawning Threads
来源：互联网 发布：广播电视台和广电网络 编辑：程序博客网 时间：2024/06/08 00:28
看了下tutorial04，这个例子生成了2个新的线程来处理播放。
不同的线程之间需要同步，一下就复杂起来了。我加了一些调试信息帮助我理解代码。
程序代码
// tutorial04.c// A pedagogical video player that will stream through every video frame as fast as it can,// and play audio (out of sync).//// This tutorial was written by Stephen Dranger (dranger@gmail.com).//// Code based on FFplay, Copyright (c) 2003 Fabrice Bellard, // and a tutorial by Martin Bohme (boehme@inb.uni-luebeckREMOVETHIS.de)// Tested on Gentoo, CVS version 5/01/07 compiled with GCC 4.1.1//// Use the Makefile to build all the samples.//// Run using// tutorial04 myvideofile.mpg//// to play the video stream on your screen.extern "C"{#include "libavutil/avstring.h"#include "libavutil/mathematics.h"#include "libavutil/pixdesc.h"#include "libavutil/imgutils.h"#include "libavutil/dict.h"#include "libavutil/parseutils.h"#include "libavutil/samplefmt.h"#include "libavutil/avassert.h"#include "libavutil/time.h"#include "libavformat/avformat.h"#include "libavdevice/avdevice.h"#include "libswscale/swscale.h"#include "libavutil/opt.h"#include "libavcodec/avfft.h"#include "libswresample/swresample.h"#include "SDL1.2/SDL.h"#include "SDL1.2/SDL_thread.h"}#pragma comment(lib, "avcodec.lib")#pragma comment(lib, "avformat.lib")#pragma comment(lib, "avutil.lib")#pragma comment(lib, "avdevice.lib")#pragma comment(lib, "avfilter.lib")#pragma comment(lib, "postproc.lib")#pragma comment(lib, "swresample.lib")#pragma comment(lib, "swscale.lib")#pragma comment(lib, "SDL.lib")#ifdef __MINGW32__#undef main /* Prevents SDL from overriding main() */#endif#include <stdio.h>#include <math.h>#define SDL_AUDIO_BUFFER_SIZE 1024#define MAX_AUDIO_FRAME_SIZE 192000#define MAX_AUDIOQ_SIZE (5 * 16 * 1024)#define MAX_VIDEOQ_SIZE (5 * 256 * 1024)#define FF_ALLOC_EVENT (SDL_USEREVENT)#define FF_REFRESH_EVENT (SDL_USEREVENT + 1)#define FF_QUIT_EVENT (SDL_USEREVENT + 2)#define VIDEO_PICTURE_QUEUE_SIZE 1typedef struct PacketQueue { AVPacketList *first_pkt, *last_pkt; int nb_packets; int size; // 用于packet_queue_put & packet_queue_get之间的同步 SDL_mutex *mutex; SDL_cond *cond;} PacketQueue;typedef struct VideoPicture { SDL_Overlay *bmp; int width, height; /* source height & width */ int allocated;} VideoPicture;typedef struct VideoState { AVFormatContext *pFormatCtx; int videoStream, audioStream; // audio AVStream *audio_st; PacketQueue audioq; uint8_t audio_buf[(MAX_AUDIO_FRAME_SIZE * 3) / 2]; unsigned int audio_buf_size; unsigned int audio_buf_index; AVFrame audio_frame; AVPacket audio_pkt; uint8_t *audio_pkt_data; int audio_pkt_size; // video // videoq中的 AVStream *video_st; PacketQueue videoq; VideoPicture pictq[VIDEO_PICTURE_QUEUE_SIZE]; int pictq_size, pictq_rindex, pictq_windex; SDL_mutex *pictq_mutex;// pictq_mutext用于互斥的访问pictq_size SDL_cond *pictq_cond; SDL_Thread *parse_tid; SDL_Thread *video_tid; char filename[1024]; int quit; AVIOContext *io_context; struct SwsContext *sws_ctx;} VideoState;SDL_Surface *screen;/* Since we only have one decoding thread, the Big Structcan be global in case we need it. */VideoState *global_video_state;struct SwrContext *swr_ctx;DECLARE_ALIGNED(16, uint8_t, audio_buf2)[MAX_AUDIO_FRAME_SIZE * 4];// BDint g_iIndex_put_video = 1;int g_iIndex_get_video = 1;// EDstatic inline double rint(double x){ return x >= 0 ? floor(x + 0.5) : ceil(x - 0.5);}void packet_queue_init(PacketQueue *q) { memset(q, 0, sizeof(PacketQueue)); q->mutex = SDL_CreateMutex(); q->cond = SDL_CreateCond();}int packet_queue_put(PacketQueue *q, AVPacket *pkt) { AVPacketList *pkt1; if( av_dup_packet(pkt) < 0 ) { return -1; } pkt1 = (AVPacketList *)av_malloc(sizeof(AVPacketList)); if( !pkt1 ) { return -1; } pkt1->pkt = *pkt; pkt1->next = NULL; SDL_LockMutex(q->mutex); if( !q->last_pkt ) { q->first_pkt = pkt1; } else { q->last_pkt->next = pkt1; } q->last_pkt = pkt1; q->nb_packets++; q->size += pkt1->pkt.size; SDL_CondSignal(q->cond); SDL_UnlockMutex(q->mutex); return 0;}static int packet_queue_get(PacketQueue *q, AVPacket *pkt, int block){ AVPacketList *pkt1; int ret; SDL_LockMutex(q->mutex); for( ; ; ) { if( global_video_state->quit ) { ret = -1; break; } pkt1 = q->first_pkt; if( pkt1 ) { q->first_pkt = pkt1->next; if( !q->first_pkt ) { q->last_pkt = NULL; } q->nb_packets--; q->size -= pkt1->pkt.size; *pkt = pkt1->pkt; av_free(pkt1); ret = 1; break; } else if (!block) { ret = 0; break; } else { SDL_CondWait(q->cond, q->mutex); } } SDL_UnlockMutex(q->mutex); return ret;}int audio_decode_frame(VideoState *is) { int len1, data_size = 0; AVPacket *pkt = &is->audio_pkt; for( ; ; ) { while(is->audio_pkt_size > 0) { int got_frame = 0; len1 = avcodec_decode_audio4(is->audio_st->codec, &is->audio_frame, &got_frame, pkt); if( len1 < 0 ) { /* if error, skip frame */ is->audio_pkt_size = 0; break; } if( got_frame ) { AVCodecContext* aCodecCtx = is->audio_st->codec; uint64_t dec_channel_layout = (aCodecCtx->channel_layout && aCodecCtx->channels == av_get_channel_layout_nb_channels(aCodecCtx->channel_layout)) ? aCodecCtx->channel_layout : av_get_default_channel_layout(aCodecCtx->channels); AVSampleFormat tgtFmt = AV_SAMPLE_FMT_S16; if( aCodecCtx->sample_fmt != tgtFmt ) { // 需要重采样 if( swr_ctx == NULL ) { swr_ctx = swr_alloc(); swr_ctx = swr_alloc_set_opts(swr_ctx, dec_channel_layout, tgtFmt, aCodecCtx->sample_rate, dec_channel_layout, aCodecCtx->sample_fmt, aCodecCtx->sample_rate, 0, NULL); if( !swr_ctx || swr_init(swr_ctx) < 0 ) { assert(false); } } if( swr_ctx ) { const uint8_t **in = (const uint8_t **)is->audio_frame.extended_data; uint8_t *out[] = {audio_buf2}; int out_count = sizeof(audio_buf2) / aCodecCtx->channels / av_get_bytes_per_sample(aCodecCtx->sample_fmt); int len2 = swr_convert(swr_ctx, out, out_count, in, is->audio_frame.nb_samples); if( len2 < 0 ) { LogPrintfA("swr_convert() failed\n"); break; } if( len2 == out_count ) { LogPrintfA("warning: audio buffer is probably too small\n"); swr_init(swr_ctx); } data_size = len2 * aCodecCtx->channels * av_get_bytes_per_sample(tgtFmt); memcpy(is->audio_buf, audio_buf2, data_size); } } else { // 不需要重采样 data_size = av_samples_get_buffer_size(NULL, aCodecCtx->channels, is->audio_frame.nb_samples, aCodecCtx->sample_fmt, 1); //assert(data_size <= buf_size); memcpy(is->audio_buf, is->audio_frame.data[0], data_size); } } is->audio_pkt_data += len1; is->audio_pkt_size -= len1; if( data_size <= 0 ) { /* No data yet, get more frames */ continue; } /* We have data, return it and come back for more later */ return data_size; } if(pkt->data) av_free_packet(pkt); if(is->quit) { return -1; } /* next packet */ if(packet_queue_get(&is->audioq, pkt, 1) < 0) { return -1; } is->audio_pkt_data = pkt->data; is->audio_pkt_size = pkt->size; }}void audio_callback(void *userdata, Uint8 *stream, int len) { VideoState *is = (VideoState *)userdata; int len1, audio_size; while(len > 0) { if(is->audio_buf_index >= is->audio_buf_size) { /* We have already sent all our data; get more */ audio_size = audio_decode_frame(is); if(audio_size < 0) { /* If error, output silence */ is->audio_buf_size = 1024; memset(is->audio_buf, 0, is->audio_buf_size); } else { is->audio_buf_size = audio_size; } is->audio_buf_index = 0; } len1 = is->audio_buf_size - is->audio_buf_index; if(len1 > len) len1 = len; memcpy(stream, (uint8_t *)is->audio_buf + is->audio_buf_index, len1); len -= len1; stream += len1; is->audio_buf_index += len1; }}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); return 0; /* 0 means stop timer */}/* schedule a video refresh in 'delay' ms */static void schedule_refresh(VideoState *is, int delay) { SDL_AddTimer(delay, sdl_refresh_timer_cb, is);}void video_display(VideoState *is) { SDL_Rect rect; VideoPicture *vp; //AVPicture pict; float aspect_ratio; int w, h, x, y; //int i; // BD static int iIndex = 1; LogPrintf(_T("[%04d] -- iIndex: %d, is->pictq_rindex: %d\n"), ::GetCurrentThreadId(), iIndex ++, is->pictq_rindex); // ED vp = &is->pictq[is->pictq_rindex]; if( vp->bmp ) { if( is->video_st->codec->sample_aspect_ratio.num == 0 ) { aspect_ratio = 0; } else { aspect_ratio = av_q2d(is->video_st->codec->sample_aspect_ratio) * is->video_st->codec->width / is->video_st->codec->height; } if( aspect_ratio <= 0.0 ) { aspect_ratio = (float)is->video_st->codec->width / (float)is->video_st->codec->height; } h = screen->h; w = ((int)rint(h * aspect_ratio)) & -3; if( w > screen->w ) { w = screen->w; h = ((int)rint(w / aspect_ratio)) & -3; } x = (screen->w - w) / 2; y = (screen->h - h) / 2; rect.x = x; rect.y = y; rect.w = w; rect.h = h; SDL_DisplayYUVOverlay(vp->bmp, &rect); }}// 定时触发播放事件, 在主线程被调用void video_refresh_timer(void *userdata) { // BD DWORD dwThreadId = ::GetCurrentThreadId(); LogPrintf(_T("[%04d] -- video_refresh_timer\n"), dwThreadId); // ED VideoState *is = (VideoState *)userdata; // vp is used in later tutorials for synchronization //VideoPicture *vp; if( is->video_st ) { if( is->pictq_size == 0 ) { schedule_refresh(is, 1); } else { //vp = &is->pictq[is->pictq_rindex]; /* Now, normally here goes a ton of code about timing, etc. we're just going to guess at a delay for now. You can increase and decrease this value and hard code the timing - but I don't suggest that ;) We'll learn how to do it for real later. */ // 播放下一帧视频的时间 schedule_refresh(is, 80); /* show the picture! */ video_display(is); /* update queue for next picture! */ if( ++ is->pictq_rindex == VIDEO_PICTURE_QUEUE_SIZE ) { is->pictq_rindex = 0; } SDL_LockMutex(is->pictq_mutex); is->pictq_size --; SDL_CondSignal(is->pictq_cond); SDL_UnlockMutex(is->pictq_mutex); } } else { schedule_refresh(is, 100); }}void alloc_picture(void *userdata){ LogPrintf(_T("[%04d] -- In alloc_picture\n"), GetCurrentThreadId()); VideoState *is = (VideoState *)userdata; VideoPicture *vp; vp = &is->pictq[is->pictq_windex]; if( vp->bmp ) { // we already have one make another, bigger/smaller SDL_FreeYUVOverlay(vp->bmp); } // Allocate a place to put our YUV image on that screen vp->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);}// 该函数中video_thread里被调用, 需要和主线程同步int queue_picture(VideoState *is, AVFrame *pFrame) { VideoPicture *vp; AVPicture pict; /* wait until we have space for a new pic */ SDL_LockMutex(is->pictq_mutex); // BD DWORD dwThreadId = ::GetCurrentThreadId(); LogPrintf(_T("[%04d] -- queue_picture, is->pictq_size: %d\n"), dwThreadId, is->pictq_size); // ED while( is->pictq_size >= VIDEO_PICTURE_QUEUE_SIZE && !is->quit ) { // 调用SDL_CondWait后, 当前线程进入等待状态, 等待pictq_cond被触发 // 此时能触发pictq_cond的地方只有video_refresh_timer函数里面了 SDL_CondWait(is->pictq_cond, is->pictq_mutex); } SDL_UnlockMutex(is->pictq_mutex); if( is->quit ) { return -1; } // windex is set to 0 initially vp = &is->pictq[is->pictq_windex]; /* allocate or resize the buffer! */ if( !vp->bmp || vp->width != is->video_st->codec->width || vp->height != is->video_st->codec->height ) { LogPrintf(_T("[%04d] -- Before push FF_ALLOC_EVENT...\n"), ::GetCurrentThreadId()); 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);// 这是个异步的事件 LogPrintf(_T("[%04d] -- After push FF_ALLOC_EVENT...\n"), ::GetCurrentThreadId()); /* wait until we have a picture allocated */ SDL_LockMutex(is->pictq_mutex); while( !vp->allocated && !is->quit ) { // 当前线程暂停, 等待alloc_picture里面的SDL_CondSignal触发is->pictq_cond, 本线程才可继续进行 SDL_CondWait(is->pictq_cond, is->pictq_mutex); } SDL_UnlockMutex(is->pictq_mutex); if( is->quit ) { return -1; } LogPrintf(_T("[%04d] -- After push FF_ALLOC_EVENT22222222222...\n"), ::GetCurrentThreadId()); } /* We have a place to put our picture on the queue */ if( vp->bmp ) { SDL_LockYUVOverlay(vp->bmp); /* point pict at the queue */ pict.data[0] = vp->bmp->pixels[0]; pict.data[1] = vp->bmp->pixels[2]; pict.data[2] = vp->bmp->pixels[1]; pict.linesize[0] = vp->bmp->pitches[0]; pict.linesize[1] = vp->bmp->pitches[2]; pict.linesize[2] = vp->bmp->pitches[1]; // Convert the image into YUV format that SDL uses sws_scale ( is->sws_ctx, (uint8_t const * const *)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;}// 此线程主要用户播放视频int video_thread(void *arg){ VideoState *is = (VideoState *)arg; AVPacket pkt1, *packet = &pkt1; int frameFinished; AVFrame *pFrame; pFrame = av_frame_alloc(); for( ; ; ) { if( packet_queue_get(&is->videoq, packet, 1) < 0 ) { // means we quit getting packets break; } // Decode video frame avcodec_decode_video2(is->video_st->codec, pFrame, &frameFinished, packet); //LogPrintf(_T("%d: packet_queue_get video: frameFinished: %s ...\n"), g_iIndex_get_video ++, frameFinished ? _T("TRUE") : _T("FALSE")); // Did we get a video frame? if( frameFinished ) { if( queue_picture(is, pFrame) < 0 ) { break; } } av_free_packet(packet); } av_free(pFrame); return 0;}int stream_component_open(VideoState *is, int stream_index) { AVFormatContext *pFormatCtx = is->pFormatCtx; AVCodecContext *codecCtx = NULL; AVCodec *codec = NULL; AVDictionary *optionsDict = NULL; SDL_AudioSpec wanted_spec, spec; if(stream_index < 0 || stream_index >= pFormatCtx->nb_streams) { return -1; } // Get a pointer to the codec context for the video stream codecCtx = pFormatCtx->streams[stream_index]->codec; // 仅对音频的处理 if( codecCtx->codec_type == AVMEDIA_TYPE_AUDIO ) { // Set audio settings from codec info wanted_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) < 0) { fprintf(stderr, "SDL_OpenAudio: %s\n", SDL_GetError()); return -1; } } // 打开音频or视频的编解码器 codec = avcodec_find_decoder(codecCtx->codec_id); if( !codec || (avcodec_open2(codecCtx, codec, &optionsDict) < 0) ) { fprintf(stderr, "Unsupported codec!\n"); return -1; } // switch( codecCtx->codec_type ) { case AVMEDIA_TYPE_AUDIO: { is->audioStream = stream_index; is->audio_st = pFormatCtx->streams[stream_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 AVMEDIA_TYPE_VIDEO: { is->videoStream = stream_index; is->video_st = pFormatCtx->streams[stream_index]; packet_queue_init(&is->videoq); is->video_tid = SDL_CreateThread(video_thread, is); is->sws_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_BILINEAR, NULL, NULL, NULL ); } break; default: break; } return 0;}int decode_interrupt_cb(void *opaque) { return (global_video_state && global_video_state->quit);}int decode_thread(void *arg){ VideoState *is = (VideoState *)arg; AVFormatContext *pFormatCtx = NULL; AVPacket pkt1, *packet = &pkt1; int video_index = -1; int audio_index = -1; int i; AVDictionary *io_dict = NULL; AVIOInterruptCB callback; is->videoStream = -1; is->audioStream = -1; global_video_state = is; // will interrupt blocking functions if we quit! callback.callback = decode_interrupt_cb; callback.opaque = is; if( avio_open2(&is->io_context, is->filename, 0, &callback, &io_dict) ) { fprintf(stderr, "Unable to open I/O for %s\n", is->filename); return -1; } // Open video file if( avformat_open_input(&pFormatCtx, is->filename, NULL, NULL) != 0 ) { return -1; // Couldn't open file } is->pFormatCtx = pFormatCtx; // Retrieve stream information if( avformat_find_stream_info(pFormatCtx, NULL) < 0 ) { return -1; // Couldn't find stream information } // Dump information about file onto standard error av_dump_format(pFormatCtx, 0, is->filename, 0); // Find the first video stream for( i = 0; i < pFormatCtx->nb_streams; i ++) { if( pFormatCtx->streams[i]->codec->codec_type == AVMEDIA_TYPE_VIDEO && video_index < 0) { video_index = i; } if( pFormatCtx->streams[i]->codec->codec_type == AVMEDIA_TYPE_AUDIO && audio_index < 0) { audio_index = i; } } if( audio_index >= 0 ) { stream_component_open(is, audio_index); } if( video_index >= 0 ) { stream_component_open(is, video_index); } if( is->videoStream < 0 || is->audioStream < 0 ) { fprintf(stderr, "%s: could not open codecs\n", is->filename); goto fail; } // Begin -- set video size by oldmtn // Make a screen to put our video#ifndef __DARWIN__ int width = pFormatCtx->streams[video_index]->codec->width; int height = pFormatCtx->streams[video_index]->codec->height; screen = SDL_SetVideoMode(width, height, 0, 0);#else screen = SDL_SetVideoMode(640, 480, 24, 0);#endif if( !screen ) { fprintf(stderr, "SDL: could not set video mode - exiting\n"); exit(1); } // End -- set video size by oldmtn // main decode loop for( ; ; ) { if( is->quit ) { break; } // seek stuff goes here if( is->audioq.size > MAX_AUDIOQ_SIZE || is->videoq.size > MAX_VIDEOQ_SIZE ) { SDL_Delay(10); continue; } if( av_read_frame(is->pFormatCtx, packet) < 0 ) { if( is->pFormatCtx->pb->error == 0 ) { SDL_Delay(100); /* no error; wait for user input */ continue; } else { break; } } // Is this a packet from the video stream? if( packet->stream_index == is->videoStream ) { //LogPrintf(_T("%d, video packet_queue_put\n"), g_iIndex_put_video ++); 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: if( 1 ) { SDL_Event event; event.type = FF_QUIT_EVENT; event.user.data1 = is; SDL_PushEvent(&event); } return 0;}int _tmain(){ SDL_Event event; VideoState *is; is = (VideoState*)av_mallocz(sizeof(VideoState)); char szFile[] = "zmj.flv"; // Register all formats and codecs av_register_all(); if( SDL_Init(SDL_INIT_VIDEO | SDL_INIT_AUDIO | SDL_INIT_TIMER) ) { fprintf(stderr, "Could not initialize SDL - %s\n", SDL_GetError()); exit(1); } av_strlcpy(is->filename, szFile, 1024); is->pictq_mutex = SDL_CreateMutex(); is->pictq_cond = SDL_CreateCond(); schedule_refresh(is, 40); is->parse_tid = SDL_CreateThread(decode_thread, is); if( !is->parse_tid ) { av_free(is); return -1; } for( ; ; ) { SDL_WaitEvent(&event); switch(event.type) { case FF_QUIT_EVENT: case SDL_QUIT: { is->quit = 1; /* * If the video has finished playing, then both the picture and * audio queues are waiting for more data. Make them stop * waiting and terminate normally. */ SDL_CondSignal(is->audioq.cond); SDL_CondSignal(is->videoq.cond); SDL_Quit(); } return 0; break; case FF_ALLOC_EVENT: { alloc_picture(event.user.data1); } break; case FF_REFRESH_EVENT: { video_refresh_timer(event.user.data1); } break; default: break; } } return 0;}我们来区分一下各个线程。
1. 主线程
这里命名为main thread， 它主要的代码在这里
for( ; ; ) { SDL_WaitEvent(&event); switch(event.type) { case FF_QUIT_EVENT: case SDL_QUIT: { is->quit = 1; /* * If the video has finished playing, then both the picture and * audio queues are waiting for more data. Make them stop * waiting and terminate normally. */ SDL_CondSignal(is->audioq.cond); SDL_CondSignal(is->videoq.cond); SDL_Quit(); } return 0; break; case FF_ALLOC_EVENT: { alloc_picture(event.user.data1); } break; case FF_REFRESH_EVENT: { video_refresh_timer(event.user.data1); } break; default: break; } }这里就是不断的执行video_refresh_timer来播放视频帧。2. decode_thread
代码
int decode_thread(void *arg){ VideoState *is = (VideoState *)arg; AVFormatContext *pFormatCtx = NULL; AVPacket pkt1, *packet = &pkt1; int video_index = -1; int audio_index = -1; int i; AVDictionary *io_dict = NULL; AVIOInterruptCB callback; is->videoStream = -1; is->audioStream = -1; global_video_state = is; // will interrupt blocking functions if we quit! callback.callback = decode_interrupt_cb; callback.opaque = is; if( avio_open2(&is->io_context, is->filename, 0, &callback, &io_dict) ) { fprintf(stderr, "Unable to open I/O for %s\n", is->filename); return -1; } // Open video file if( avformat_open_input(&pFormatCtx, is->filename, NULL, NULL) != 0 ) { return -1; // Couldn't open file } is->pFormatCtx = pFormatCtx; // Retrieve stream information if( avformat_find_stream_info(pFormatCtx, NULL) < 0 ) { return -1; // Couldn't find stream information } // Dump information about file onto standard error av_dump_format(pFormatCtx, 0, is->filename, 0); // Find the first video stream for( i = 0; i < pFormatCtx->nb_streams; i ++) { if( pFormatCtx->streams[i]->codec->codec_type == AVMEDIA_TYPE_VIDEO && video_index < 0) { video_index = i; } if( pFormatCtx->streams[i]->codec->codec_type == AVMEDIA_TYPE_AUDIO && audio_index < 0) { audio_index = i; } } if( audio_index >= 0 ) { stream_component_open(is, audio_index); } if( video_index >= 0 ) { stream_component_open(is, video_index); } if( is->videoStream < 0 || is->audioStream < 0 ) { fprintf(stderr, "%s: could not open codecs\n", is->filename); goto fail; } // Begin -- set video size by oldmtn // Make a screen to put our video#ifndef __DARWIN__ int width = pFormatCtx->streams[video_index]->codec->width; int height = pFormatCtx->streams[video_index]->codec->height; screen = SDL_SetVideoMode(width, height, 0, 0);#else screen = SDL_SetVideoMode(640, 480, 24, 0);#endif if( !screen ) { fprintf(stderr, "SDL: could not set video mode - exiting\n"); exit(1); } // End -- set video size by oldmtn // main decode loop for( ; ; ) { if( is->quit ) { break; } // seek stuff goes here if( is->audioq.size > MAX_AUDIOQ_SIZE || is->videoq.size > MAX_VIDEOQ_SIZE ) { SDL_Delay(10); continue; } if( av_read_frame(is->pFormatCtx, packet) < 0 ) { if( is->pFormatCtx->pb->error == 0 ) { SDL_Delay(100); /* no error; wait for user input */ continue; } else { break; } } // Is this a packet from the video stream? if( packet->stream_index == is->videoStream ) { //LogPrintf(_T("%d, video packet_queue_put\n"), g_iIndex_put_video ++); 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: if( 1 ) { SDL_Event event; event.type = FF_QUIT_EVENT; event.user.data1 = is; SDL_PushEvent(&event); } return 0;}3. video_thread线程
// 此线程主要用于播放视频int video_thread(void *arg){ VideoState *is = (VideoState *)arg; AVPacket pkt1, *packet = &pkt1; int frameFinished; AVFrame *pFrame; pFrame = av_frame_alloc(); for( ; ; ) { if( packet_queue_get(&is->videoq, packet, 1) < 0 ) { // means we quit getting packets break; } // Decode video frame avcodec_decode_video2(is->video_st->codec, pFrame, &frameFinished, packet); //LogPrintf(_T("%d: packet_queue_get video: frameFinished: %s ...\n"), g_iIndex_get_video ++, frameFinished ? _T("TRUE") : _T("FALSE")); // Did we get a video frame? if( frameFinished ) { if( queue_picture(is, pFrame) < 0 ) { break; } } av_free_packet(packet); } av_free(pFrame); return 0;}这里就是不断的取视频包，并将其加入到播放缓存队列VideoPicture pictq[VIDEO_PICTURE_QUEUE_SIZE];中。为了理解不同线程之间是如何同步的，下面我打印一些调试信息，帮助我理解：
[19248] -- video_refresh_timer[19248] -- video_refresh_timer[19248] -- video_refresh_timer[19248] -- video_refresh_timer[19248] -- video_refresh_timer[19248] -- video_refresh_timer[19360] -- queue_picture, is->pictq_size: 0[19360] -- Before push FF_ALLOC_EVENT...[19360] -- After push FF_ALLOC_EVENT...[19248] -- video_refresh_timer[19248] -- In alloc_picture[19248] -- video_refresh_timer[19360] -- After push FF_ALLOC_EVENT22222222222...[19360] -- queue_picture, is->pictq_size: 1[19248] -- video_refresh_timer[19248] -- iIndex: 1, is->pictq_rindex: 0
可以看到在video thread的queue_picture里输出了
[19360] -- queue_picture, is->pictq_size: 0
该函数触发了FF_ALLOC_EVENT事件后，调用了SDL_CondWait(is->pictq_cond, is->pictq_mutex);就使video thread陷入了等待状态。
而FF_ALLOC_EVENT事件触发了main thread的alloc_picture里面的SDL_CondSignal(is->pictq_cond);而正是这个信号使得video thread可以继续执行。
这3个线程之间的逻辑图如下所示：
SDL_mutex *pictq_mutex;// pictq_mutext用于互斥的访问pictq_size
SDL_cond *pictq_cond;
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