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1.stream_open()
static VideoState *stream_open(const char *filename, AVInputFormat *iformat) { // 数据初始化 VideoState *is; is = av_mallocz(sizeof(VideoState)); /* 分配结构体并初始化 */ if (!is) return NULL; is->filename = av_strdup(filename); if (!is->filename) goto fail; is->iformat = iformat; is->ytop = 0; is->xleft = 0; /* 初始化帧队列 */ if (frame_queue_init(&is->pictq, &is->videoq, VIDEO_PICTURE_QUEUE_SIZE, 1) < 0) goto fail; if (frame_queue_init(&is->subpq, &is->subtitleq, SUBPICTURE_QUEUE_SIZE, 0) < 0) goto fail; if (frame_queue_init(&is->sampq, &is->audioq, SAMPLE_QUEUE_SIZE, 1) < 0) goto fail; if (packet_queue_init(&is->videoq) < 0 || packet_queue_init(&is->audioq) < 0 || packet_queue_init(&is->subtitleq) < 0) goto fail; /* 创建 */ if (!(is->continue_read_thread = SDL_CreateCond())) { av_log(NULL, AV_LOG_FATAL, "SDL_CreateCond(): %s ", SDL_GetError()); goto fail; } /* * 初始化时钟 * 时钟序列->queue_serial，实际上指向的是is->videoq.serial */ init_clock(&is->vidclk, &is->videoq.serial); init_clock(&is->audclk, &is->audioq.serial); init_clock(&is->extclk, &is->extclk.serial); is->audio_clock_serial = -1; /* 初始化音量 */ if (startup_volume < 0) av_log(NULL, AV_LOG_WARNING, "-volume=%d < 0, setting to 0 ", startup_volume); if (startup_volume > 100) av_log(NULL, AV_LOG_WARNING, "-volume=%d > 100, setting to 100 ", startup_volume); startup_volume = av_clip(startup_volume, 0, 100); startup_volume = av_clip(SDL_MIX_MAXVOLUME * startup_volume / 100, 0, SDL_MIX_MAXVOLUME); is->audio_volume = startup_volume; is->muted = 0; // 同步类型：默认以音频为基准 is->av_sync_type = av_sync_type; /* 创建读线程 */ is->read_tid = SDL_CreateThread(read_thread, "read_thread", is); if (!is->read_tid) { av_log(NULL, AV_LOG_FATAL, "SDL_CreateThread(): %s ", SDL_GetError()); fail: stream_close(is); return NULL; } return is; }
这个比较简单，就是一些数据初始化
2. read_thread()
/* this thread gets the stream from the disk or the network */ /* * 数据都由这里读取 * 主要功能是做解复用，从码流中分离音视频packet，并插入缓存队列 */ static int read_thread(void *arg) { VideoState *is = arg; AVFormatContext *ic = NULL; int err, i, ret; int st_index[AVMEDIA_TYPE_NB]; AVPacket pkt1, *pkt = &pkt1; int64_t stream_start_time; int pkt_in_play_range = 0; AVDictionaryEntry *t; SDL_mutex *wait_mutex = SDL_CreateMutex(); int scan_all_pmts_set = 0; int64_t pkt_ts; // 一、准备流程 if (!wait_mutex) { av_log(NULL, AV_LOG_FATAL, "SDL_CreateMutex(): %s ", SDL_GetError()); ret = AVERROR(ENOMEM); goto fail; } memset(st_index, -1, sizeof(st_index)); // 初始化为-1,如果一直为-1说明没相应steam is->last_video_stream = is->video_stream = -1; is->last_audio_stream = is->audio_stream = -1; is->last_subtitle_stream = is->subtitle_stream = -1; is->eof = 0; // =1是表明数据读取完毕 // 1. 创建上下文结构体，这个结构体是最上层的结构体，表示输入上下文 ic = avformat_alloc_context(); if (!ic) { av_log(NULL, AV_LOG_FATAL, "Could not allocate context. "); ret = AVERROR(ENOMEM); goto fail; } /* 2.设置中断回调函数，如果出错或者退出，就根据目前程序设置的状态选择继续check或者直接退出 */ /* 当执行耗时操作时（一般是在执行while或者for循环的数据读取时），会调用interrupt_callback.callback * 回调函数中返回1则代表ffmpeg结束耗时操作退出当前函数的调用 * 回调函数中返回0则代表ffmpeg内部继续执行耗时操作，直到完成既定的任务(比如读取到既定的数据包) */ ic->interrupt_callback.callback = decode_interrupt_cb; ic->interrupt_callback.opaque = is; //特定选项处理 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; } /* 3.打开文件，主要是探测协议类型，如果是网络文件则创建网络链接等 */ 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. ", t->key); ret = AVERROR_OPTION_NOT_FOUND; goto fail; } is->ic = ic; // videoState的ic指向分配的ic if (genpts) ic->flags |= AVFMT_FLAG_GENPTS; 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; /* * 4.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 * codecpar, filled by libavformat on stream creation or * in avformat_find_stream_info() */ 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 parameters ", 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 */ /* 5. 检测是否指定播放起始时间 */ 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; // seek的指定的位置开始播放 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 %0.3f ", is->filename, (double)timestamp / AV_TIME_BASE); } } /* 是否为实时流媒体 */ is->realtime = is_realtime(ic); if (show_status) av_dump_format(ic, 0, is->filename, 0); // 6. 查找AVStream // 6.1 根据用户指定来查找流, 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 stream ", wanted_stream_spec[i], av_get_media_type_string(i)); // st_index[i] = INT_MAX; st_index[i] = -1; } } // 6.2 利用av_find_best_stream选择流， if (!video_disable) 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); is->show_mode = show_mode; //7 从待处理流中获取相关参数，设置显示窗口的宽度、高度及宽高比 if (st_index[AVMEDIA_TYPE_VIDEO] >= 0) { AVStream *st = ic->streams[st_index[AVMEDIA_TYPE_VIDEO]]; AVCodecParameters *codecpar = st->codecpar; /*根据流和帧宽高比猜测帧的样本宽高比。该值只是一个参考 */ AVRational sar = av_guess_sample_aspect_ratio(ic, st, NULL); if (codecpar->width) { // 设置显示窗口的大小和宽高比 set_default_window_size(codecpar->width, codecpar->height, sar); } } /* open the streams */ /* 8. 打开视频、音频解码器。在此会打开相应解码器，并创建相应的解码线程。 */ if (st_index[AVMEDIA_TYPE_AUDIO] >= 0) {// 如果有音频流则打开音频流 stream_component_open(is, st_index[AVMEDIA_TYPE_AUDIO]); } ret = -1; if (st_index[AVMEDIA_TYPE_VIDEO] >= 0) { // 如果有视频流则打开视频流 ret = stream_component_open(is, st_index[AVMEDIA_TYPE_VIDEO]); } if (is->show_mode == SHOW_MODE_NONE) { //选择怎么显示，如果视频打开成功，就显示视频画面，否则，显示音频对应的频谱图 is->show_mode = ret >= 0 ? SHOW_MODE_VIDEO : SHOW_MODE_RDFT; } if (st_index[AVMEDIA_TYPE_SUBTITLE] >= 0) { // 如果有字幕流则打开字幕流 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 filtergraph ", is->filename); ret = -1; goto fail; } if (infinite_buffer < 0 && is->realtime) infinite_buffer = 1; // 如果是实时流 /* * 二、For循环流程 */ for (;;) { // 1 检测是否退出 if (is->abort_request) break; // 2 检测是否暂停/继续 if (is->paused != is->last_paused) { is->last_paused = is->paused; if (is->paused) is->read_pause_return = av_read_pause(ic); // 网络流的时候有用 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 */ // 等待10ms，避免立马尝试下一个Packet SDL_Delay(10); continue; } #endif // 3 检测是否seek if (is->seek_req) { // 是否有seek请求 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 // 修复由于四舍五入，没有再seek_pos/seek_rel变量的正确方向上进行 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 seeking ", is->ic->url); } else { /* seek的时候，要把原先的数据情况，并重启解码器，put flush_pkt的目的是告知解码线程需要 * reset decoder */ if (is->audio_stream >= 0) { // 如果有音频流 packet_queue_flush(&is->audioq); // 清空packet队列数据 // 放入flush pkt, 用来开起新的一个播放序列, 解码器读取到flush_pkt也清空解码器 packet_queue_put(&is->audioq, &flush_pkt); } if (is->subtitle_stream >= 0) { // 如果有字幕流 packet_queue_flush(&is->subtitleq); // 和上同理 packet_queue_put(&is->subtitleq, &flush_pkt); } if (is->video_stream >= 0) { // 如果有视频流 packet_queue_flush(&is->videoq); // 和上同理 packet_queue_put(&is->videoq, &flush_pkt); } 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); } } is->seek_req = 0; is->queue_attachments_req = 1; is->eof = 0; if (is->paused) step_to_next_frame(is); } // 4 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) { AVPacket copy = { 0 }; if ((ret = av_packet_ref(©, &is->video_st->attached_pic)) < 0) goto fail; packet_queue_put(&is->videoq, ©); packet_queue_put_nullpacket(&is->videoq, is->video_stream); } is->queue_attachments_req = 0; } // 5 检测队列是否已经有足够数据 /* if the queue are full, no need to read more */ /* 缓存队列有足够的包，不需要继续读取数据 15M * 8 / 3(Mbps) = 40秒*/ 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); // 如果没有唤醒则超时10ms退出，比如在seek操作时这里会被唤醒 SDL_CondWaitTimeout(is->continue_read_thread, wait_mutex, 10); SDL_UnlockMutex(wait_mutex); continue; } // 6 检测码流是否已经播放结束 if (!is->paused // 非暂停 && // 这里的执行是因为码流读取完毕后 插入空包所致 (!is->audio_st // 没有音频流 || (is->auddec.finished == is->audioq.serial // 或者音频播放完毕 && frame_queue_nb_remaining(&is->sampq) == 0)) && (!is->video_st // 没有视频流 || (is->viddec.finished == is->videoq.serial // 或者视频播放完毕 && frame_queue_nb_remaining(&is->pictq) == 0))) { if (loop != 1 // a 是否循环播放 && (!loop || --loop)) { // stream_seek不是ffmpeg的函数，是ffplay封装的，每次seek的时候会调用 stream_seek(is, start_time != AV_NOPTS_VALUE ? start_time : 0, 0, 0); } else if (autoexit) { // b 是否自动退出 ret = AVERROR_EOF; goto fail; } } // 7.读取媒体数据，得到的是音视频分离后、解码前的数据 ret = av_read_frame(ic, pkt); // 调用不会释放pkt的数据，需要我们自己去释放packet的数据 // 8 检测数据是否读取完毕 if (ret < 0) { if ((ret == AVERROR_EOF || avio_feof(ic->pb)) && !is->eof) { // 插入空包说明码流数据读取完毕了，之前讲解码的时候说过刷空包是为了从解码器把所有帧都读出来 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; // 文件读取完毕 } if (ic->pb && ic->pb->error) break; SDL_LockMutex(wait_mutex); SDL_CondWaitTimeout(is->continue_read_thread, wait_mutex, 10); SDL_UnlockMutex(wait_mutex); continue; // 继续循环 } else { is->eof = 0; } // 9 检测是否在播放范围内 /* check if packet is in play range specified by user, then queue, otherwise discard */ stream_start_time = ic->streams[pkt->stream_index]->start_time; // 获取流的起始时间 pkt_ts = pkt->pts == AV_NOPTS_VALUE ? pkt->dts : pkt->pts; // 获取packet的时间戳 // 这里的duration是在命令行时用来指定播放长度 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); // 10 将音视频数据分别送入相应的queue中 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)) { //printf("pkt pts:%ld, dts:%ld ", pkt->pts, pkt->dts); 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);// // 不入队列则直接释放数据 } } // 三 退出线程处理 ret = 0; fail: if (ic && !is->ic) avformat_close_input(&ic); if (ret != 0) { SDL_Event event; event.type = FF_QUIT_EVENT; event.user.data1 = is; SDL_PushEvent(&event); } SDL_DestroyMutex(wait_mutex); return 0; }