音视频技术(6)-iOS音视频同步

• 2020 年 3 月 27 日
• 筆記

这部分内容较多，涉及多个线程协同实现“解复用”、“解音频帧”、“解视频”、“音频&视频渲染”，前后研究了两周多，还有些代码没理解为什么这么写。

盗用一张@MzDavid画的图，逻辑很清楚

音视频同步播放流程

网上绝大多数代码都是参照ffplay来实现的，下面按照接入流程一步步讲解如何实现iOS平台上音视频同步

1. iOS接入ffmpeg和SDL可以参考前面的文章，本文不做赘述。main函数里做初始化VideoState（上下文）、SDL和开启线程的工作，新版本的ffmpeg已经不需要再av_regist_all这样的调用了，VideoState可以理解为存储各种临时信息和上下文的结构体，包括各线程处理的数据也存在VideoState里，避免各个线程之间直接的调用，VideoState起到状态机的作用，解耦各线程的工作。 详细的代码在文章结尾有贴出来 main函数里：

• 创建demux_thread(解复用线程)
• 触发一次延时渲染视频帧的任务 schedule_refresh(is, 40); （后面在视频帧渲染里自己持续发消息触发自己渲染，直到没有更多视频帧或者出错）

1. 解复用(或者说解封装，解包) 打开文件 & 读取文件的媒体信息 –> 开启子线程解具体的每一帧(取包的时候，如果没有会等待解复用) –> for循环中不断的读每一帧 –> 队列里存放packet

解复用流程

1. 打开流 这一步按流程可以整合到解复用中，但是涉及到音频和视频解复用的部分有重复的代码，从代码结构设计上抽象出来是合理的。 另外，在这一步开启了音频硬件准备和读取的线程(SDL_PauseAudio，这个方法会在合适时机，以回调的方式获取音频帧并渲染) 。 同时，打开了新的线程解析视频帧(decode_video_thread，把解析的视频帧入到VideoState的队列中)

打开流并解析音视频帧

注意几点 1.新版本ffmpeg里，新增api,avcodec_parameters_to_context(…)用来获取解码参数 2.新的解码方法，和渲染的api不兼容，需要重采样处理，使用API:swr_convert，这里代码有一点没明白，// 重采样，转换成ffmpeg能播放的采样率，还没理解swr_convert的逻辑，while循环里后面的audio_buf不会把前面的冲掉么？

// 重采样，转换成ffmpeg能播放的采样率，还没理解这swr_convert的逻辑，while循环里后面的audio_buf不会把前面的冲掉么？  swr_convert(is->audio_swr_ctx,                      &audio_buf,                      MAX_AUDIO_FRAME_SIZE * 3/2,                      (const uint8_t **) is->audio_frame.data,                      is->audio_frame.nb_samples);

1. 视频解码 注意两点：

• 新版ffmpeg的API，和老的ffmpeg不同，使用avcode_send_packet和avcode_receive_frame成对使用，而且一个send可能对应多个receive，所以使用while循环多次调用receive，笔者打日志发现实际情况恰恰相反，一开始有多个send调用，而receive只有单次调用(费解)。
• 视频解码需要将pts自然数转成秒值，以和音频同步，音视频同步有多种方法，基于人对声音比较敏感，一般采用视频同步到音频。

1. synchronize_video,生成视频PTS 这一步，还没彻底弄明白 分两步：1)pts转换成ms值，作为渲染的delay值，如果该视频帧有重复，即画面没有变化，则要加上一个额外的delay值，如下代码所示，重复的次数 * 单帧时间，没明白的是为什么要 * 0.5呢？可能是经验？费解。

frame_delay += src_frame->repeat_pict * (frame_delay * 0.5);

1. 视频帧队列处理 比较简单，入队列的操作，有一点不确定的是 VIDEO_PICTURE_QUEUE_SIZE值是1，队列里始终只有1帧，有视频帧就等待，等待这一帧被消费了之后才放进来，这个队列有什么意义呢？可能也能设置成任意值，看开发者的使用场景吧，不过这里时间关系（懒惰），笔者没有去试着改这个数
2. video_refresh_timer，视频刷新 这步稍微复杂点，通过对比音频帧时间戳，来动态调整视频的下次刷新时机

生成下次视频帧渲染时间

sync_threshold的计算

1. 剩下的非核心代码逻辑，可以参考前面音频 和 视频渲染讲解，没有复杂之处 本篇文章花的时间较长，反复研读代码才基本明白是怎么回事，想要再进一步理解，还得去读ffmpeg的源码实现，当前阶段先不做深入了解，比这更重要的是把整个音视频处理大的流程和基本原理磕清楚，后面再回过头找价值高的地方深入进去。

音视频处理确实涉及的技术比较深，与笔者当前的工作并不match，只能在不多的休息时间里再挤一点时间，日拱一卒去学习钻研，加油。

9.完整代码

#include "SimplePlayer.h"  #include <stdio.h>  #include <libavcodec/avcodec.h>  #include <libavformat/avformat.h>  #include <libswscale/swscale.h>  #include <libavutil/time.h>  #include <libswresample/swresample.h>  #include <SDL.h>  #include <math.h>  #include <assert.h>  #include <SDL_main.h>  #import <VideoToolbox/VideoToolbox.h>  #import <AVFoundation/AVFoundation.h>  #import <GameController/GameController.h>  #import <CoreMotion/CoreMotion.h>    #define SDL_AUDIO_BUFFER_SIZE 1024  #define MAX_AUDIO_FRAME_SIZE 192000    // 没明白 5 * 16 * 1024 是怎么规定的  #define MAX_AUDIOQ_SIZE (5 * 16 * 1024)  #define MAX_VIDEOQ_SIZE (5 * 256 * 1024)    #define AV_SYNC_THRESHOLD 0.01  #define AV_NOSYNC_THRESHOLD 10.0    #define FF_REFRESH_EVENT (SDL_USEREVENT)  #define FF_QUIT_EVENT (SDL_USEREVENT + 1)    #define VIDEO_PICTURE_QUEUE_SIZE 1    typedef struct PacketQueue{      AVPacketList *first_pkt, *last_pkt;      int nb_packets;      int size;      SDL_mutex *mutex;      SDL_cond *cond;  } PacketQueue;    typedef struct VideoPicture{      AVFrame *frame;      int width, height;      double pts;  } VideoPicture;    typedef struct VideoState {      char filename[1024];      AVFormatContext *pFormatCtx;      int videoStream, audioStream;        double audio_clock;      double frame_timer;      double frame_last_pts;      double frame_last_delay;        double video_clock;      double video_current_pts;      int64_t video_current_pts_time;        AVStream *audio_st;      AVCodecContext *audio_ctx;      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;      int audio_hw_buf_size;      struct SwrContext *audio_swr_ctx;        AVStream *video_st;      AVCodecContext *video_ctx;      PacketQueue videoq;        VideoPicture pictq[VIDEO_PICTURE_QUEUE_SIZE];      //rindex read_index 一般表示循环队列结尾处，      //windex write_index 一般表示循环队列开始处，      int pictq_size, pictq_rindex, pictq_windex;      SDL_mutex *pictq_mutex;      SDL_cond *pictq_cond;        SDL_Thread *parse_tid;      SDL_Thread *video_tid;        int quit;  } VideoState;    char *file ;    SDL_mutex *text_mutex;  SDL_Window *win = NULL;  SDL_Renderer *renderer;  SDL_Texture *texture;      static int screen_left = SDL_WINDOWPOS_CENTERED;  static int screen_top = SDL_WINDOWPOS_CENTERED;  static int screen_width = 0;  static int screen_height = 0;  static int resize = 1;    VideoState *global_video_state;    //  //SDL_Event event;  //VideoState *is;  //    void packet_queue_init(PacketQueue *q){      printf("n");        printf("packet_queue_initn");      memset(q, 0, sizeof(PacketQueue));      q->mutex = SDL_CreateMutex();      q->cond = SDL_CreateCond();  }    int packet_queue_put(PacketQueue *q, AVPacket *pkt){  //    printf("packet_queue_putn");      AVPacketList *pkt1;      if (av_packet_make_refcounted(pkt) < 0){          return -1;      }      pkt1 = 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;  }    int packet_queue_get(PacketQueue *q, AVPacket *pkt, int block){  //    printf("packet_queue_getn");      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;  }    double get_audio_clock(VideoState *is){      printf("n");        printf("get_audio_clockn");      double pts;      int hw_buf_size, bytes_per_sec, n;        pts = is->audio_clock;        hw_buf_size = is->audio_buf_size - is->audio_buf_index;        bytes_per_sec = 0;        n = is->audio_ctx ->channels * 2;      if(is->audio_st){          bytes_per_sec = is->audio_ctx->sample_rate * n;      }      if(bytes_per_sec){          pts -= (double)hw_buf_size / bytes_per_sec;      }      return pts;  }      int audio_decode_frame(VideoState *is, uint8_t *audio_buf, int buf_size, double *pts_ptr){      printf("audio_decode_framen");      int len1, data_size = 0;      AVPacket *pkt = &is->audio_pkt;      double pts;      int n;        for (;;) {          printf("audio_decode_frame---forn");          while (is->audio_pkt_size > 0) {              // 打日志发现 send重复很多次，receive一般一次，而且swr_convert 一般一次，              // 这里加while 逻辑可能是部分编码格式一次会receive多帧              avcodec_send_packet(is->audio_ctx, pkt);              printf("audio_decode_frame---sendn");              while (avcodec_receive_frame(is->audio_ctx, &is->audio_frame) == 0) {                  printf("audio_decode_frame---receiven");                  len1 = is->audio_frame.pkt_size;                    if(len1 < 0){                      is->audio_pkt_size = 0;                      printf("audio_decode_frame---breakn");                      break;                  }                    data_size = 2 * is->audio_frame.nb_samples * 2;                  assert(data_size <= buf_size);                    // 重采样，转换成ffmpeg能播放的采样率，还没理解这swr_convert的逻辑，while循环里后面的audio_buf不会把前面的冲掉么？                  swr_convert(is->audio_swr_ctx,                              &audio_buf,                              MAX_AUDIO_FRAME_SIZE * 3/2,                              (const uint8_t **) is->audio_frame.data,                              is->audio_frame.nb_samples);                  printf("audio_decode_frame---swr_convert  audio_buf = %lun", sizeof(audio_buf));                }              is->audio_pkt_data += len1;              is->audio_pkt_size -=len1;              if(data_size <= 0){                  continue;              }              pts = is->audio_clock;              *pts_ptr = pts;              n = 2 * is->audio_ctx->channels;              is->audio_clock += (double) data_size / (double)(n * is->audio_ctx -> sample_rate);              return data_size;          }            if(pkt -> data){              av_packet_unref(pkt);          }            if(is->quit){              return -1;          }            if(packet_queue_get(&is->audioq, pkt, 1) < 0){              return -1;          }            is->audio_pkt_data = pkt->data;          is->audio_pkt_size = pkt->size;            if(pkt->pts != AV_NOPTS_VALUE){              is->audio_clock = av_q2d(is->audio_st->time_base) * pkt->pts;          }      }  }    void audio_callback(void *userdata, Uint8 *stream, int len){      printf("n");        printf("audio_callback len = %dn", len);      VideoState *is = (VideoState *)userdata;      int len1, audio_size;      double pts;        SDL_memset(stream, 0, len);        while (len > 0) {          if(is->audio_buf_index >= is->audio_buf_size){              audio_size = audio_decode_frame(is, is->audio_buf, sizeof(is->audio_buf), &pts);              if(audio_size < 0){                  printf("audio_callback errorn");                  is->audio_buf_size = 1024 * 2 * 2;                  memset(is->audio_buf, 0, is->audio_buf_size);              } else {                  is->audio_buf_size = audio_size;                  printf("audio_callback audio_size %dn", audio_size);              }              is->audio_buf_index = 0;          }            len1 = is->audio_buf_size - is->audio_buf_index;          if(len1 > len){              len1 = len;          }            SDL_MixAudio(stream, (uint8_t*) is->audio_buf + is->audio_buf_index, len1, SDL_MIX_MAXVOLUME);          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;  }    static void schedule_refresh(VideoState *is, int delay){  //    printf("schedule_refreshn");      SDL_AddTimer(delay, sdl_refresh_timer_cb, is);  }    void video_display(VideoState *is){      printf("n");        printf("video_displayn");      SDL_Rect rect;      VideoPicture *vp;        if(screen_width && resize){          SDL_SetWindowSize(win, screen_width, screen_height);          SDL_SetWindowPosition(win, screen_left, screen_top);          SDL_ShowWindow(win);            Uint32 pixformat = SDL_PIXELFORMAT_IYUV;            texture = SDL_CreateTexture(renderer,                                       pixformat,                                       SDL_TEXTUREACCESS_STREAMING,                                       screen_width,                                       screen_height);          resize = 0;      }        vp = &is->pictq[is->pictq_rindex];        if(vp->frame){          SDL_UpdateYUVTexture(texture, NULL,                               vp->frame->data[0],vp->frame->linesize[0],                               vp->frame->data[1],vp->frame->linesize[1],                               vp->frame->data[2],vp->frame->linesize[2]);        }      rect.x = 0;      rect.y = 0;      rect.w = is->video_ctx->width;      rect.h = is->video_ctx->height;      SDL_LockMutex(text_mutex);      SDL_RenderClear(renderer);      SDL_RenderCopy(renderer, texture, NULL, &rect);      SDL_RenderPresent(renderer);      SDL_UnlockMutex(text_mutex);  }      void video_refresh_timer(void *userdata){  //    printf("video_refresh_timern");      VideoState *is = (VideoState *) userdata;      VideoPicture *vp;      double actual_delay, delay, sync_threshold, ref_clock, diff;        if(is->video_st){          if(is->pictq_size == 0){              schedule_refresh(is, 1);          } else {              vp = &is->pictq[is->pictq_rindex];                is->video_current_pts = vp->pts;              is->video_current_pts_time = av_gettime();                delay = vp->pts - is->frame_last_pts;              if(delay <= 0 || delay >= 1.0){                  delay = is->frame_last_delay;              }                is->frame_last_delay = delay;              is->frame_last_pts = vp->pts;                ref_clock = get_audio_clock(is);                diff = vp->pts - ref_clock;                sync_threshold = (delay > AV_SYNC_THRESHOLD) ? delay : AV_SYNC_THRESHOLD;              if(fabs(diff) < AV_NOSYNC_THRESHOLD){                  if(diff <= -sync_threshold){                      delay = 0;                  } else if(diff >= sync_threshold){                      delay = 2 * delay;                  }              }                is->frame_timer += delay;                actual_delay = is->frame_timer - (av_gettime()/1000000.0);              if(actual_delay < 0.010){                  actual_delay = 0.010;              }                schedule_refresh(is, (int)(actual_delay * 1000 + 0.5));                video_display(is);                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);      }  }    int queue_picture(VideoState *is, AVFrame *pFrame, double pts){      printf("n");        printf("queue_picturen");      VideoPicture *vp;        SDL_LockMutex(is->pictq_mutex);      // VIDEO_PICTURE_QUEUE_SIZE  == 1 ，只有1帧，不做过多缓存，原因不明，可以尝试调大这个参数      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;      }        vp = &is->pictq[is->pictq_windex];        if(!vp->frame ||         vp->width != is->video_ctx->width ||         vp->height != is->video_ctx->height){            vp ->frame = av_frame_alloc();          if(is->quit){              return -1;          }      }        if(vp->frame){          vp->pts = pts;            vp->frame = pFrame;            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;  }    double synchronize_video(VideoState *is, AVFrame *src_frame, double pts){      printf("n");        printf("synchronize_videon");      double frame_delay;      if(pts != 0){          is->video_clock = pts;      } else {          pts = is->video_clock;      }        frame_delay = av_q2d(is->video_ctx->time_base);        frame_delay += src_frame->repeat_pict * (frame_delay * 0.5);      is->video_clock += frame_delay;      return pts;  }      int decode_video_thread(void *arg){      printf("n");        printf("decode_video_threadn");      VideoState *is = (VideoState *) arg;      AVPacket pkt1, *packet = &pkt1;      AVFrame *pFrame;      double pts;        pFrame = av_frame_alloc();        for (;;) {          if(packet_queue_get(&is->videoq, packet, 1)<0){              break;          }            avcodec_send_packet(is->video_ctx, packet);          while (avcodec_receive_frame(is->video_ctx, pFrame) == 0) {              if((pts = pFrame->best_effort_timestamp) != AV_NOPTS_VALUE){                } else {                  pts = 0;              }                pts *=av_q2d(is->video_st->time_base);                pts = synchronize_video(is, pFrame, pts);              if(queue_picture(is, pFrame, pts) < 0){                  break;              }                av_packet_unref(packet);          }      }      av_frame_free(&pFrame);      return 0;  }    int stream_component_open(VideoState *is, int stream_index){      printf("n");      printf("stream_component_open index = %dn", stream_index);      AVFormatContext *pFormatCtx = is->pFormatCtx;      AVCodecContext *codecCtx = NULL;      AVCodec *codec = NULL;      SDL_AudioSpec wanted_spec;        if(stream_index < 0 || stream_index >= pFormatCtx->nb_streams){          return -1;      }      codecCtx = avcodec_alloc_context3(NULL);      int ret = avcodec_parameters_to_context(codecCtx, pFormatCtx->streams[stream_index]->codecpar);      if(ret < 0){          return -1;      }        codec = avcodec_find_decoder(codecCtx->codec_id);      printf("codec_id = %dn", codecCtx->codec_id);      if(!codec){          fprintf(stderr,"Unsupported codec!n");          return -1;      }        if(avcodec_open2(codecCtx, codec, NULL) < 0){          fprintf(stderr, "Unsupported codec !n");      }        switch (codecCtx->codec_type) {          case AVMEDIA_TYPE_AUDIO:              printf("stream_component_open----AUDIOn");              wanted_spec.freq = codecCtx->sample_rate;              wanted_spec.format = AUDIO_S16SYS;              wanted_spec.channels = 2;              wanted_spec.silence = 0;              wanted_spec.samples = SDL_AUDIO_BUFFER_SIZE;              wanted_spec.callback = audio_callback;              wanted_spec.userdata = is;              fprintf(stderr, "wanted spec: channels:%d, sample_fmt:%d, sample_rate:%d n", 2, AUDIO_S16SYS, codecCtx->sample_rate);                if(SDL_OpenAudio(&wanted_spec, NULL) < 0){                  fprintf(stderr, "SDL_OpenAudio:%sn", SDL_GetError());                  return -1;              }                is->audioStream = stream_index;              is->audio_st = pFormatCtx->streams[stream_index];              is->audio_ctx = codecCtx;              is->audio_buf_size = 0;                is->audio_buf_index = 0;              memset(&is->audio_pkt, 0, sizeof(is->audio_pkt));              packet_queue_init(&is->audioq);              uint64_t out_channel_layout = AV_CH_LAYOUT_STEREO;              int out_nb_samples = is->audio_ctx->frame_size;                int out_sample_rate = is->audio_ctx->sample_rate;              int out_channels = av_get_channel_layout_nb_channels(out_channel_layout);                int64_t in_channel_layout = av_get_default_channel_layout(is->audio_ctx->channels);                struct SwrContext *audio_convert_ctx;              audio_convert_ctx = swr_alloc();              swr_alloc_set_opts(audio_convert_ctx,                                 out_channel_layout,                                 AV_SAMPLE_FMT_S16,                                 out_sample_rate,                                 in_channel_layout,                                 is->audio_ctx->sample_fmt,                                 is->audio_ctx->sample_rate,                                 0,                                 NULL);              swr_init(audio_convert_ctx);              is->audio_swr_ctx = audio_convert_ctx;                SDL_PauseAudio(0);              break;          case AVMEDIA_TYPE_VIDEO:              printf("stream_component_open----VIDEOn");              is->videoStream = stream_index;              is->video_st = pFormatCtx->streams[stream_index];              is->video_ctx = codecCtx;                is->frame_timer = (double) av_gettime() / 1000000.0;              // 初始化刷新值 40ms，应该就是经验值，没有特殊之处              is->frame_last_delay = 40e-3;              is->video_current_pts_time = av_gettime();                packet_queue_init(&is->videoq);                is->video_tid = SDL_CreateThread(decode_video_thread, "Decode_video_thread", is);              break;            default:              break;      }        return 0;  }    //int err_code;  //char *errors;  //  //AVFormatContext *pFormatCtx;  //AVPacket *packet;    int demux_thread(void *arg){      printf("n");      printf("demux_threadn");      int err_code;      char errors[1024] = {0,};      int w,h;      VideoState *is = (VideoState *)arg;      AVFormatContext *pFormatCtx = NULL;      AVPacket pkt1, *packet = &pkt1;        int video_index = -1;      int audio_index = -1;      int i;        is->videoStream = -1;      is->audioStream = -1;        global_video_state = is;        if((err_code = avformat_open_input(&pFormatCtx, is->filename, NULL, NULL)) < 0){          av_strerror(err_code, errors, 1024);          printf("Could not open source file %s, %d(%s)n", is->filename, err_code, errors);          return -1;      }        is->pFormatCtx = pFormatCtx;      if(avformat_find_stream_info(pFormatCtx, NULL) < 0){          return -1;      }  //    av_dump_format(pFormatCtx, 0, is->filename, 0);        for (i=0; i<pFormatCtx->nb_streams; i++) {          if(pFormatCtx->streams[i]->codecpar->codec_type == AVMEDIA_TYPE_VIDEO && video_index < 0){              video_index = i;              printf("demux_thread video_index = %dn", video_index);          }          if(pFormatCtx->streams[i]->codecpar->codec_type == AVMEDIA_TYPE_AUDIO && audio_index < 0){              audio_index = i;              printf("demux_thread audio_index = %dn", audio_index);          }      }      if(audio_index >= 0){          printf("demux_thread open audio-----n");          stream_component_open(is, audio_index);      }      if(video_index >= 0){          printf("demux_thread open video----n");          stream_component_open(is, video_index);      }        if(is->videoStream < 0 || is->audioStream < 0){          printf("%s:could not open codecsn", is->filename);          goto fail;      }        screen_width = is->video_ctx->width;      screen_height = is->video_ctx->height;        for (;;) {          if(is->quit){              break;          }            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);                  continue;              } else {                  break;              }          }            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_packet_unref(packet);          }      }      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 WinMain(){      printf("n");        SDL_Event event;      VideoState *is;        NSString *mp4file = [NSString stringWithFormat:@"resource.bundle/sintel.mov"];      NSString *mp4pth = [[[NSBundle mainBundle] resourcePath] stringByAppendingPathComponent:mp4file];      file = [mp4pth UTF8String];      printf("winmain--startn");      is = av_mallocz(sizeof(VideoState));        SDL_SetMainReady();      if(SDL_Init(SDL_INIT_VIDEO | SDL_INIT_AUDIO | SDL_INIT_TIMER)){          fprintf(stderr, "Could not initialize SDL -%sn", SDL_GetError());          exit(1);      }        win = SDL_CreateWindow("Media",                             100,100,                             640,480,                             SDL_WINDOW_RESIZABLE);      printf("create windown");        if(!win){          fprintf(stderr, "SDL_CreateWindow error, exit! -%s", SDL_GetError());          exit(1);      }        renderer = SDL_CreateRenderer(win, -1, 0);      text_mutex = SDL_CreateMutex();      strlcpy(is->filename, file, sizeof(is->filename));      is->pictq_mutex = SDL_CreateMutex();      is->pictq_cond = SDL_CreateCond();        schedule_refresh(is, 40);        is->parse_tid = SDL_CreateThread(demux_thread, "demux_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;                  goto Destroy;                  break;              case SDL_KEYDOWN:                  break;              case FF_REFRESH_EVENT:                  video_refresh_timer(event.user.data1);                  break;              default:                  break;          }      }        Destroy:      SDL_Quit();        printf("end n");      return 0;  }