AVFormatContext
start_time 参数意义
：stream的开始时间。这个是时间是音视频帧最小时间戳。
一、ffmpeg中代码实现：
//获取每个流Streams中第一音频或者视频帧时间戳：
image.png
static void update_initial_timestamps(AVFormatContext *s, int stream_index,
int64_t dts, int64_t pts, AVPacket *pkt)
if (st->start_time == AV_NOPTS_VALUE) { //取各个stream开始时间
if (st->codecpar->codec_type == AVMEDIA_TYPE_AUDIO || !(pkt->flags & AV_PKT_FLAG_DISCARD)) {
st->start_time = pts;
}
if (st->codecpar->codec_type == AVMEDIA_TYPE_AUDIO && st->codecpar->sample_rate)
st->start_time += av_rescale_q(st->skip_samples, (AVRational){1, st->codecpar->sample_rate}, st->time_base);
}
开始给AVFormatContext的start_time赋值
小算法 比较相邻的stream 开始时间，最后选择最小的给AVFormatContext赋值
static void update_stream_timings(AVFormatContext *ic){
start_time = INT64_MAX;
start_time_text = INT64_MAX;
...
for (i = 0; i < ic->nb_streams; i++) {
AVStream *st = ic->streams[i];
int is_text = st->codecpar->codec_type == AVMEDIA_TYPE_SUBTITLE ||
st->codecpar->codec_type == AVMEDIA_TYPE_DATA;
if (st->start_time != AV_NOPTS_VALUE && st->time_base.den) {
start_time1 = av_rescale_q(st->start_time, st->time_base,
AV_TIME_BASE_Q);
if (is_text)
start_time_text = FFMIN(start_time_text, start_time1); // 取小值
else
start_time = FFMIN(start_time, start_time1); // 取小值
...
}
} // end of for
// 比较
if (start_time == INT64_MAX || (start_time > start_time_text && start_time - (uint64_t)start_time_text < AV_TIME_BASE))
start_time = start_time_text;
else if (start_time > start_time_text)
av_log(ic, AV_LOG_VERBOSE, "Ignoring outlier non primary stream starttime %f\n", start_time_text / (float)AV_TIME_BASE);
...
if (start_time != INT64_MAX) {
ic->start_time = start_time; // 赋值
...
}
}
二、ffprobe看一个具体的例子，关于这个时间start_time
所有帧数据的音频时间戳：
ffprobe -show_packets -select_streams a https://yaya-resource.cdnjtzy.com/video/005f382e97fbd5b6715aae720caecec6_1280x720_20210324230522-000.ts | grep pts_time
image.png
所有视频帧的时间戳：
ffprobe -show_packets -select_streams a https://yaya-resource.cdnjtzy.com/video/005f382e97fbd5b6715aae720caecec6_1280x720_20210324230522-000.ts | grep pts_time
image.png
三、去掉start_time
-max_delay 0
ffmpeg -i **.mp4 -f mpegts -max_delay 0 aaa.ts
然后再切流
ffmpeg -i record.ts -max_muxing_queue_size 9999 -vcodec copy -g 40 -c:a copy -strict -2 -f hls -hls_time 4 -hls_list_size 0 -bsf:v h264_mp4toannexb record.m3u8
image.png
