Tutorial 04: Spawning Threads

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 ([email protected]).
//
// Code based on FFplay, Copyright (c) 2003 Fabrice Bellard, 
// and a tutorial by Martin Bohme ([email protected])
// 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    1

typedef 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 Struct
can 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];

// BD
int g_iIndex_put_video = 1;
int g_iIndex_get_video = 1;
// ED

static 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;
}

这个decode_thread，里面有一个for循环，不断的取各个音视频包，并调用packet_queue_put，将其加入到队列中。同时在其他线程里面会调用packet_queue_get来取这些音视频包，在读或者取这些音视频包的时候，是线程同步的。

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：

而main thread和video thread之间线程的同步是通过VideoState的如下2个成员实现同步的。

SDL_mutex       *pictq_mutex;// pictq_mutext用于互斥的访问pictq_size
SDL_cond        *pictq_cond;