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。
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：
/**
* 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：
static 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
// 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。
// 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
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