avformat.h

/**
 * Open an input stream and read the header. The codecs are not opened.
 * The stream must be closed with avformat_close_input().
 *
 * @param ps Pointer to user-supplied AVFormatContext (allocated by avformat_alloc_context).
 *           May be a pointer to NULL, in which case an AVFormatContext is allocated by this
 *           function and written into ps.
 *           Note that a user-supplied AVFormatContext will be freed on failure.
 * @param url URL of the stream to open.
 * @param fmt If non-NULL, this parameter forces a specific input format.
 *            Otherwise the format is autodetected.
 * @param options  A dictionary filled with AVFormatContext and demuxer-private options.
 *                 On return this parameter will be destroyed and replaced with a dict containing
 *                 options that were not found. May be NULL.
 *
 * @return 0 on success, a negative AVERROR on failure.
 *
 * @note If you want to use custom IO, preallocate the format context and set its pb field.
 */
int avformat_open_input(AVFormatContext **ps, const char *url, AVInputFormat *fmt, AVDictionary **options);

avpackettextunit-run.m

- (void)run{
    self.onPacketBufferFullBlock = ^(){
        
    };
    self.onPacketBufferEmptyBlock = ^(){
        
    };
    
    [self prepareToRead];
    [self readPacket];
    
    self.timer = [NSTimer scheduledTimerWithTimeInterval:1.0 target:self selector:@selector(onTimer) userInfo:nil repeats:YES];
    self.second = 0;
    
    [[NSRunLoop mainRunLoop] addTimer:self.timer forMode:NSRunLoopCommonModes];
}

- (void)onTimer{
    
    // 每过3秒消耗一次数据包
    // 随机决定“消耗一个数据包”还是“消耗所有数据包”
    if(self.second % 3 == 0){
        int randomNumber = arc4random_uniform(2);
        if(randomNumber == 0){
            // 消耗所有数据包
            av_packet_queue_flush(&audioq);
            av_packet_queue_flush(&videoq);
            
            self.packetBufferIsFull = NO;
            self.packetBufferIsEmpty = YES;
            
            NSLog(@"# %ds - comsume all packets,now audioq = %d, videoq = %d", (int)self.second, audioq.nb_packets, videoq.nb_packets);
        }
        else{
            // 消耗一个数据包
            AVPacket audioPkt;
            int audioqNotEmpty = av_packet_queue_get(&audioq, &audioPkt, 0);
            if(audioqNotEmpty){
                av_packet_unref(&audioPkt);
            }
            
            AVPacket videoPkt;
            int videoqNotEmpty = av_packet_queue_get(&videoq, &videoPkt, 0);
            if(videoqNotEmpty){
                av_packet_unref(&videoPkt);
            }
            
            self.packetBufferIsFull = NO;
            if(!audioqNotEmpty && !videoqNotEmpty){
                self.packetBufferIsEmpty = YES;
            }
            
            NSLog(@"# %ds - comsume one packet, now audioq = %d, videoq = %d", (int)self.second, audioq.nb_packets, videoq.nb_packets);
        }
    }
    else{
        NSLog(@"# %ds - packet buffer is %@full, now audioq = %d, videoq = %d",(int)self.second, self.packetBufferIsFull ? @"":@"not ", audioq.nb_packets, videoq.nb_packets);
    }
    self.second += 1;
}

ffplay-read-thread.c

ret = av_read_frame(ic, pkt);
if (ret < 0) {
    if ((ret == AVERROR_EOF || avio_feof(ic->pb)) && !is->eof) {
        if (is->video_stream >= 0)
            packet_queue_put_nullpacket(&is->videoq, is->video_stream);
        if (is->audio_stream >= 0)
            packet_queue_put_nullpacket(&is->audioq, is->audio_stream);
        if (is->subtitle_stream >= 0)
            packet_queue_put_nullpacket(&is->subtitleq, is->subtitle_stream);
        is->eof = 1;
    }
    if (ic->pb && ic->pb->error) {
        if (autoexit)
            goto fail;
        else
            break;
    }