在前面我们介绍了ffplay的总体架构和一些关键的数据结构。今天我们还是从这张图开始，主要介绍ffplay的读取线程部分。
图导出的可能有点模糊，再加上上传图床后不知道有没有更加模糊了，想要高清大图的可以后台留言，加v信索取。
从ffplay的main函数入口开始阅读源码，发现是在函数stream_open创建了资源读取线程，读取线程执行的函数是read_thread，所以要分析读取线程的工作内容，我们只需读懂函数read_thread即可。
下面是我加了注释的read_thread函数：
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364/** * 读取线程工作内容 * @param arg * @return */ static int read_thread(void *arg) { VideoState *is = arg; AVFormatContext *ic = NULL; int err, i, ret; int st_index[AVMEDIA_TYPE_NB]; AVPacket *pkt = NULL; int64_t stream_start_time; int pkt_in_play_range = 0; const AVDictionaryEntry *t; // 互斥量，读取线程总不能一直读取吧，播放消费队列消费比不上读取的速度，队列满了就要陷入等待唤醒 SDL_mutex *wait_mutex = SDL_CreateMutex(); int scan_all_pmts_set = 0; int64_t pkt_ts; if (!wait_mutex) { av_log(NULL, AV_LOG_FATAL, "SDL_CreateMutex(): %sn", SDL_GetError()); ret = AVERROR(ENOMEM); goto fail; } // 所有流的索引都设置成-1 memset(st_index, -1, sizeof(st_index)); is->eof = 0; // 分配pack pkt = av_packet_alloc(); if (!pkt) { av_log(NULL, AV_LOG_FATAL, "Could not allocate packet.n"); ret = AVERROR(ENOMEM); goto fail; } // 解封装上下文 ic = avformat_alloc_context(); if (!ic) { av_log(NULL, AV_LOG_FATAL, "Could not allocate context.n"); ret = AVERROR(ENOMEM); goto fail; } // 回调函数，防止读取过程中阻塞时间过长 ic->interrupt_callback.callback = decode_interrupt_cb; ic->interrupt_callback.opaque = is; if (!av_dict_get(format_opts, "scan_all_pmts", NULL, AV_DICT_MATCH_CASE)) { av_dict_set(&format_opts, "scan_all_pmts", "1", AV_DICT_DONT_OVERWRITE); scan_all_pmts_set = 1; } // 打开 err = avformat_open_input(&ic, is->filename, is->iformat, &format_opts); if (err < 0) { print_error(is->filename, err); ret = -1; goto fail; } if (scan_all_pmts_set) av_dict_set(&format_opts, "scan_all_pmts", NULL, AV_DICT_MATCH_CASE); if ((t = av_dict_get(format_opts, "", NULL, AV_DICT_IGNORE_SUFFIX))) { av_log(NULL, AV_LOG_ERROR, "Option %s not found.n", t->key); ret = AVERROR_OPTION_NOT_FOUND; goto fail; } is->ic = ic; if (genpts) ic->flags |= AVFMT_FLAG_GENPTS; // 将其注入成一个变量 av_format_inject_global_side_data(ic); if (find_stream_info) { AVDictionary **opts = setup_find_stream_info_opts(ic, codec_opts); int orig_nb_streams = ic->nb_streams; /* * 探测媒体类型，可得到当前文件的封装格式，音视频编码参数等信息 * 调用该函数后得多的参数信息会比只调用avformat_open_input更为详细， * 其本质上是去做了decdoe packet获取信息的工作 */ err = avformat_find_stream_info(ic, opts); for (i = 0; i < orig_nb_streams; i++) av_dict_free(&opts[i]); av_freep(&opts); if (err < 0) { av_log(NULL, AV_LOG_WARNING, "%s: could not find codec parametersn", is->filename); ret = -1; goto fail; } } if (ic->pb) ic->pb->eof_reached = 0; // FIXME hack, ffplay maybe should not use avio_feof() to test for the end if (seek_by_bytes < 0) seek_by_bytes = !!(ic->iformat->flags & AVFMT_TS_DISCONT) && strcmp("ogg", ic->iformat->name); is->max_frame_duration = (ic->iformat->flags & AVFMT_TS_DISCONT) ? 10.0 : 3600.0; if (!window_title && (t = av_dict_get(ic->metadata, "title", NULL, 0))) window_title = av_asprintf("%s - %s", t->value, input_filename); /* if seeking requested, we execute it */ // 起始播放时间处理 if (start_time != AV_NOPTS_VALUE) { int64_t timestamp; timestamp = start_time; /* add the stream start time */ if (ic->start_time != AV_NOPTS_VALUE) timestamp += ic->start_time; // 跳到播放位置 ret = avformat_seek_file(ic, -1, INT64_MIN, timestamp, INT64_MAX, 0); if (ret < 0) { av_log(NULL, AV_LOG_WARNING, "%s: could not seek to position %0.3fn", is->filename, (double)timestamp / AV_TIME_BASE); } } // 是否是时时流 is->realtime = is_realtime(ic); if (show_status) // 打印媒体信息 av_dump_format(ic, 0, is->filename, 0); // 流索引相关 for (i = 0; i < ic->nb_streams; i++) { AVStream *st = ic->streams[i]; enum AVMediaType type = st->codecpar->codec_type; st->discard = AVDISCARD_ALL; if (type >= 0 && wanted_stream_spec[type] && st_index[type] == -1) if (avformat_match_stream_specifier(ic, st, wanted_stream_spec[type]) > 0) st_index[type] = i; } for (i = 0; i < AVMEDIA_TYPE_NB; i++) { if (wanted_stream_spec[i] && st_index[i] == -1) { av_log(NULL, AV_LOG_ERROR, "Stream specifier %s does not match any %s streamn", wanted_stream_spec[i], av_get_media_type_string(i)); st_index[i] = INT_MAX; } } if (!video_disable) // 查找视频流索引 st_index[AVMEDIA_TYPE_VIDEO] = av_find_best_stream(ic, AVMEDIA_TYPE_VIDEO, st_index[AVMEDIA_TYPE_VIDEO], -1, NULL, 0); if (!audio_disable) st_index[AVMEDIA_TYPE_AUDIO] = av_find_best_stream(ic, AVMEDIA_TYPE_AUDIO, st_index[AVMEDIA_TYPE_AUDIO], st_index[AVMEDIA_TYPE_VIDEO], NULL, 0); if (!video_disable && !subtitle_disable) st_index[AVMEDIA_TYPE_SUBTITLE] = av_find_best_stream(ic, AVMEDIA_TYPE_SUBTITLE, st_index[AVMEDIA_TYPE_SUBTITLE], (st_index[AVMEDIA_TYPE_AUDIO] >= 0 ? st_index[AVMEDIA_TYPE_AUDIO] : st_index[AVMEDIA_TYPE_VIDEO]), NULL, 0); // 更新视频信息初始化窗口参数 is->show_mode = show_mode; if (st_index[AVMEDIA_TYPE_VIDEO] >= 0) { AVStream *st = ic->streams[st_index[AVMEDIA_TYPE_VIDEO]]; AVCodecParameters *codecpar = st->codecpar; AVRational sar = av_guess_sample_aspect_ratio(ic, st, NULL); if (codecpar->width) set_default_window_size(codecpar->width, codecpar->height, sar); } /* open the streams */ // 打开视频流，内不创建了解码线程 if (st_index[AVMEDIA_TYPE_AUDIO] >= 0) { stream_component_open(is, st_index[AVMEDIA_TYPE_AUDIO]); } ret = -1; // 打开音频流 if (st_index[AVMEDIA_TYPE_VIDEO] >= 0) { ret = stream_component_open(is, st_index[AVMEDIA_TYPE_VIDEO]); } if (is->show_mode == SHOW_MODE_NONE) is->show_mode = ret >= 0 ? SHOW_MODE_VIDEO : SHOW_MODE_RDFT; // 打开字幕流 if (st_index[AVMEDIA_TYPE_SUBTITLE] >= 0) { stream_component_open(is, st_index[AVMEDIA_TYPE_SUBTITLE]); } if (is->video_stream < 0 && is->audio_stream < 0) { av_log(NULL, AV_LOG_FATAL, "Failed to open file '%s' or configure filtergraphn", is->filename); ret = -1; goto fail; } if (infinite_buffer < 0 && is->realtime) infinite_buffer = 1; // 循环读取 for (;;) { // 是否退出了 if (is->abort_request) break; // 更新是否暂停了 if (is->paused != is->last_paused) { is->last_paused = is->paused; if (is->paused) is->read_pause_return = av_read_pause(ic); else av_read_play(ic); } #if CONFIG_RTSP_DEMUXER || CONFIG_MMSH_PROTOCOL if (is->paused && (!strcmp(ic->iformat->name, "rtsp") || (ic->pb && !strncmp(input_filename, "mmsh:", 5)))) { /* wait 10 ms to avoid trying to get another packet */ /* XXX: horrible */ SDL_Delay(10); continue; } #endif // 是否seek了 if (is->seek_req) { int64_t seek_target = is->seek_pos; int64_t seek_min = is->seek_rel > 0 ? seek_target - is->seek_rel + 2: INT64_MIN; int64_t seek_max = is->seek_rel < 0 ? seek_target - is->seek_rel - 2: INT64_MAX; // FIXME the +-2 is due to rounding being not done in the correct direction in generation // of the seek_pos/seek_rel variables ret = avformat_seek_file(is->ic, -1, seek_min, seek_target, seek_max, is->seek_flags); if (ret < 0) { av_log(NULL, AV_LOG_ERROR, "%s: error while seekingn", is->ic->url); } else { // seek了要刷新待解码包队列 if (is->audio_stream >= 0) packet_queue_flush(&is->audioq); if (is->subtitle_stream >= 0) packet_queue_flush(&is->subtitleq); if (is->video_stream >= 0) packet_queue_flush(&is->videoq); if (is->seek_flags & AVSEEK_FLAG_BYTE) { set_clock(&is->extclk, NAN, 0); } else { set_clock(&is->extclk, seek_target / (double)AV_TIME_BASE, 0); } } // seek复位 is->seek_req = 0; is->queue_attachments_req = 1; is->eof = 0; if (is->paused) step_to_next_frame(is); } // 检测video是否为attached_pic if (is->queue_attachments_req) { // attached_pic 附带的图片。比如说一些MP3，AAC音频文件附带的专辑封面，所以需要注意的是音频文件不一定只存在音频流本身 if (is->video_st && is->video_st->disposition & AV_DISPOSITION_ATTACHED_PIC) { if ((ret = av_packet_ref(pkt, &is->video_st->attached_pic)) < 0) goto fail; packet_queue_put(&is->videoq, pkt); packet_queue_put_nullpacket(&is->videoq, pkt, is->video_stream); } is->queue_attachments_req = 0; } /* if the queue are full, no need to read more */ // 队列是否有足够的包 if (infinite_buffer<1 && (is->audioq.size + is->videoq.size + is->subtitleq.size > MAX_QUEUE_SIZE || (stream_has_enough_packets(is->audio_st, is->audio_stream, &is->audioq) && stream_has_enough_packets(is->video_st, is->video_stream, &is->videoq) && stream_has_enough_packets(is->subtitle_st, is->subtitle_stream, &is->subtitleq)))) { /* wait 10 ms */ SDL_LockMutex(wait_mutex); SDL_CondWaitTimeout(is->continue_read_thread, wait_mutex, 10); SDL_UnlockMutex(wait_mutex); continue; } // 播放完了，看是否需要重播 if (!is->paused && (!is->audio_st || (is->auddec.finished == is->audioq.serial && frame_queue_nb_remaining(&is->sampq) == 0)) && (!is->video_st || (is->viddec.finished == is->videoq.serial && frame_queue_nb_remaining(&is->pictq) == 0))) { if (loop != 1 && (!loop || --loop)) { // 这里的重播就不用再次从新走一次逻辑了，直接seek就好了 stream_seek(is, start_time != AV_NOPTS_VALUE ? start_time : 0, 0, 0); } else if (autoexit) { ret = AVERROR_EOF; goto fail; } } // 读取一个包 ret = av_read_frame(ic, pkt); if (ret < 0) { // 读到末尾了，放入空包，以便后续冲刷解码器 if ((ret == AVERROR_EOF || avio_feof(ic->pb)) && !is->eof) { if (is->video_stream >= 0) packet_queue_put_nullpacket(&is->videoq, pkt, is->video_stream); if (is->audio_stream >= 0) packet_queue_put_nullpacket(&is->audioq, pkt, is->audio_stream); if (is->subtitle_stream >= 0) packet_queue_put_nullpacket(&is->subtitleq, pkt, is->subtitle_stream); is->eof = 1; } if (ic->pb && ic->pb->error) { if (autoexit) goto fail; else break; } // 休息一会，但是可以被唤醒，有需求你就去干 SDL_LockMutex(wait_mutex); SDL_CondWaitTimeout(is->continue_read_thread, wait_mutex, 10); SDL_UnlockMutex(wait_mutex); continue; } else { is->eof = 0; } // 将包放入队列前先检查这个包是否在播放的时间之内 /* check if packet is in play range specified by user, then queue, otherwise discard */ stream_start_time = ic->streams[pkt->stream_index]->start_time; pkt_ts = pkt->pts == AV_NOPTS_VALUE ? pkt->dts : pkt->pts; pkt_in_play_range = duration == AV_NOPTS_VALUE || (pkt_ts - (stream_start_time != AV_NOPTS_VALUE ? stream_start_time : 0)) * av_q2d(ic->streams[pkt->stream_index]->time_base) - (double)(start_time != AV_NOPTS_VALUE ? start_time : 0) / 1000000 <= ((double)duration / 1000000); // 将包放入队列 if (pkt->stream_index == is->audio_stream && pkt_in_play_range) { packet_queue_put(&is->audioq, pkt); } else if (pkt->stream_index == is->video_stream && pkt_in_play_range && !(is->video_st->disposition & AV_DISPOSITION_ATTACHED_PIC)) { packet_queue_put(&is->videoq, pkt); } else if (pkt->stream_index == is->subtitle_stream && pkt_in_play_range) { packet_queue_put(&is->subtitleq, pkt); } else { av_packet_unref(pkt); } } ret = 0; fail: if (ic && !is->ic) avformat_close_input(&ic); av_packet_free(&pkt); if (ret != 0) { SDL_Event event; event.type = FF_QUIT_EVENT; event.user.data1 = is; SDL_PushEvent(&event); } SDL_DestroyMutex(wait_mutex); return 0; }
读取线程准备工作
1、创建读取线程互斥量SDL_CreateMutex
2、分配AVPacket，av_packet_alloc
3、分配解封装上下文avformat_alloc_context
4、设置回调函数ic->interrupt_callback.callback
5、打开媒体文件avformat_open_input
6、avformat_find_stream_info探测媒体信息
7、是否需要起始seek播放avformat_seek_file
8、获取流索引
9、stream_component_open初始化相关解码器组件
在ffplay读取线程的准备工作中，我们发现一个检查是否是实时流的方法，它是这样子判断的：
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16static int is_realtime(AVFormatContext *s) { if( !strcmp(s->iformat->name, "rtp") || !strcmp(s->iformat->name, "rtsp") || !strcmp(s->iformat->name, "sdp") ) return 1; if(s->pb && ( !strncmp(s->url, "rtp:", 4) || !strncmp(s->url, "udp:", 4) ) ) return 1; return 0; }
for循环读取
1、首先通过大内总管VideoState判断是否请求了退出
2、根据是否暂停了控制RTSP流以及SDL显示
3、处理seek操作
在这个过程中会调用函数packet_queue_flush刷新待解码包队列，然后将队列的播放序列serial加1，这就是播放序列的妙用之处。
4、检查队列中是否有足够的包，stream_has_enough_packets，如果队列满了则读取线程最多等待10ms，但是可以被唤醒。
5、播放完了，判断是否需要进行重播
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13// 播放完了，看是否需要重播 if (!is->paused && (!is->audio_st || (is->auddec.finished == is->audioq.serial && frame_queue_nb_remaining(&is->sampq) == 0)) && (!is->video_st || (is->viddec.finished == is->videoq.serial && frame_queue_nb_remaining(&is->pictq) == 0))) { if (loop != 1 && (!loop || --loop)) { // 这里的重播就不用再次从新走一次逻辑了，直接seek就好了 stream_seek(is, start_time != AV_NOPTS_VALUE ? start_time : 0, 0, 0); } else if (autoexit) { ret = AVERROR_EOF; goto fail; } }
6、av_read_frame读取一个资源包
如果读到了文件末尾则增加一个空包packet_queue_put_nullpacket，以便于后续在解码线程用于冲刷解码器，这样就能将解码器内部缓存的数据全部取出。
如果读取到的不是空包，则判断该包的pts是否处于有效播放时间内，如果不在则丢弃，如果在则放入队列packet_queue_put。
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21// 将包放入队列前先检查这个包是否在播放的时间之内 /* check if packet is in play range specified by user, then queue, otherwise discard */ stream_start_time = ic->streams[pkt->stream_index]->start_time; pkt_ts = pkt->pts == AV_NOPTS_VALUE ? pkt->dts : pkt->pts; pkt_in_play_range = duration == AV_NOPTS_VALUE || (pkt_ts - (stream_start_time != AV_NOPTS_VALUE ? stream_start_time : 0)) * av_q2d(ic->streams[pkt->stream_index]->time_base) - (double)(start_time != AV_NOPTS_VALUE ? start_time : 0) / 1000000 <= ((double)duration / 1000000); // 将包放入队列 if (pkt->stream_index == is->audio_stream && pkt_in_play_range) { packet_queue_put(&is->audioq, pkt); } else if (pkt->stream_index == is->video_stream && pkt_in_play_range && !(is->video_st->disposition & AV_DISPOSITION_ATTACHED_PIC)) { packet_queue_put(&is->videoq, pkt); } else if (pkt->stream_index == is->subtitle_stream && pkt_in_play_range) { packet_queue_put(&is->subtitleq, pkt); } else { av_packet_unref(pkt); }
7、失败处理，释放相关资源，SDL发送退出事件FF_QUIT_EVENT
推荐阅读
FFmpeg连载1-开发环境搭建
FFmpeg连载2-分离视频和音频
FFmpeg连载3-视频解码
FFmpeg连载4-音频解码
FFmpeg连载5-音视频编码
FFmpeg连载6-音频重采样
FFmpeg连载8-视频合并以及替换视频背景音乐实战
ffplay调试环境搭建
ffplay整体框架
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