Hi Martin,
OK, here I provide some codes to demo this bug. Many of these are copied from
libavformat/tests/movenc.c
#include <libavcodec/avcodec.h>
#include <libavformat/avformat.h>
#include <libavutil/opt.h>
#include <libavutil/intreadwrite.h>
static const uint8_t h264_extradata[] = {
0x01, 0x4d, 0x40, 0x1e, 0xff, 0xe1, 0x00, 0x02, 0x67, 0x4d, 0x01, 0x00,
0x02, 0x68, 0xef
};
AVPacket *pkt;
AVFormatContext *ctx;
void mux_packet(int64_t ts) {
uint8_t pktdata[8] = { 0 };
av_packet_unref(pkt);
pkt->stream_index = 0;
pkt->pts = pkt->dts = ts;
AV_WB32(pktdata + 4, pkt->pts);
pkt->data = pktdata;
pkt->size = 8;
av_write_frame(ctx, pkt);
}
int main() {
avformat_alloc_output_context2(&ctx, NULL, NULL, "bug.mp4");
// Setting this flag is important
av_opt_set(ctx, "movflags", "+frag_every_frame", AV_OPT_SEARCH_CHILDREN);
AVStream *st = avformat_new_stream(ctx, NULL);
st->codecpar->codec_type = AVMEDIA_TYPE_VIDEO;
st->codecpar->codec_id = AV_CODEC_ID_H264;
st->codecpar->width = 640;
st->codecpar->height = 480;
st->time_base.num = 1;
st->time_base.den = 30;
st->codecpar->extradata_size = sizeof(h264_extradata);
st->codecpar->extradata = av_mallocz(st->codecpar->extradata_size +
AV_INPUT_BUFFER_PADDING_SIZE);
memcpy(st->codecpar->extradata, h264_extradata, sizeof(h264_extradata));
avio_open(&ctx->pb, "bug.mp4", AVIO_FLAG_WRITE);
avformat_write_header(ctx, NULL);
pkt = av_packet_alloc();
mux_packet(0);
mux_packet(1);
mux_packet(2);
av_write_frame(ctx, NULL); // Manually flush a frag
mux_packet(10); // Automatically flush an empty frag, because
frag_every_frame is set
mux_packet(11);
mux_packet(12);
av_write_trailer(ctx);
avformat_free_context(ctx);
av_packet_free(&pkt);
}
After compile and run this code, run this command to inspect the dts (which
comes from the out of sync tfdt)
ffprobe -show_packets bug.mp4 | grep dts=
The output is:
dts=0
dts=1
dts=2
dts=2
dts=3
dts=4
With this patch applied, the output is:
dts=0
dts=1
dts=2
dts=10
dts=11
dts=12
Regards,
Hu Weiwen
On Mon, Jul 19, 2021 at 11:33:59PM +0300, Martin Storsjö wrote:
> Hi,
>
> Thanks for the patch! I'll try to look into it in a while (I'm a bit swamped
> and short on time at the moment), hopefully within a couple days or so.
>
> On Sun, 18 Jul 2021, Hu Weiwen wrote:
>
> > Fix an edge case when auto flushing an empty fragment, and the previous
> > fragment
> > has inaccurate duration, the track->frag_start would be out of sync from
> > input
> > dts, and all subsequent tfdt box will have out of sync
> > base_media_decode_time.
> > This error can accumulate to quite large over long-running streaming.
> >
> > This can be easily reproduced by remux a variable frame rate source with
> > dash
> > muxer and set streaming to 1.
>
> Can you provide a specific sample and a command line, and point out what
> values in the output file that are mismatched - so I can zoom in on the
> issue quicker once I have time to sit down and look at it?
>
> // Martin
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