[FFmpeg-devel] [PATCH 2/3] avformat/mpegtsenc: make first_pcr sync with the first valid dts

[lance.lmwang at gmail.com]

On Wed, Oct 21, 2020 at 03:41:00PM -0400, Devin Heitmueller wrote:
> On Wed, Oct 21, 2020 at 9:48 AM <lance.lmwang at gmail.com> wrote:
> >
> > From: Limin Wang <lance.lmwang at gmail.com>
> >
> > now first_pts assume dts will start from zero, if it's not true(copyts is enable),
> > too many null packet will be inserted for cbr output.
> >
> > Please test with below command, you'll get huge test.ts without the patch:
> > ./ffmpeg -y -copyts -i ../fate-suite/mpegts/loewe.ts  -c:v libx264 -x264opts \
> >    nal-hrd=cbr:force-cfr=1 -b:v 3500k -minrate 3500k -maxrate 3500k -bufsize \
> >    1000k  -c:a mp2 -muxrate 4500k  -vframes 1000 test.ts
> >
> > Signed-off-by: Limin Wang <lance.lmwang at gmail.com>
> > ---
> >  libavformat/mpegtsenc.c | 7 +++++++
> >  1 file changed, 7 insertions(+)
> >
> > diff --git a/libavformat/mpegtsenc.c b/libavformat/mpegtsenc.c
> > index e05d0ce..baea3b4 100644
> > --- a/libavformat/mpegtsenc.c
> > +++ b/libavformat/mpegtsenc.c
> > @@ -81,6 +81,7 @@ typedef struct MpegTSWrite {
> >      int64_t pat_period; /* PAT/PMT period in PCR time base */
> >      int nb_services;
> >      int64_t first_pcr;
> > +    int first_dts_check;
> >      int64_t next_pcr;
> >      int mux_rate; ///< set to 1 when VBR
> >      int pes_payload_size;
> > @@ -1136,6 +1137,7 @@ static int mpegts_init(AVFormatContext *s)
> >
> >      if (ts->copyts < 1)
> >          ts->first_pcr = av_rescale(s->max_delay, PCR_TIME_BASE, AV_TIME_BASE);
> > +    ts->first_dts_check = 1;
> >
> >      select_pcr_streams(s);
> >
> > @@ -1690,6 +1692,11 @@ static int mpegts_write_packet_internal(AVFormatContext *s, AVPacket *pkt)
> >          stream_id = side_data[0];
> >
> >      if (ts->copyts < 1) {
> > +        if (ts->first_dts_check && dts != AV_NOPTS_VALUE) {
> > +            ts->first_pcr += dts * 300;
> > +        }
> > +        ts->first_dts_check = 0;
> > +
> 
> Shouldn't the line "ts->first_dts_check = 0;" be inside the if()
> statement? Otherwise if the very first packet has a DTS of
> AV_NOPTS_VALUE then the first_pcr will never get incremented by the
> dts (since after the first run the check for first_dts_check will
> always fail).

Yes, you're right, will fix it.

> 
> FWIW, the basic change is definitely useful, as I've had a nearly
> identical patch in my tree for some time:
> 
> https://github.com/LTNGlobal-opensource/FFmpeg-ltn/commit/b974e431f7de39401a04d2c6e9bbdcc21e2982da
> 

make fate will fail if I set first_pcr to AV_NOPTS_VALUE and add later like
your changes. So I add extra flag for the check.

> Devin
> 
> -- 
> Devin Heitmueller, Senior Software Engineer
> LTN Global Communications
> o: +1 (301) 363-1001
> w: https://ltnglobal.com  e: devin.heitmueller at ltnglobal.com

-- 
Thanks,
Limin Wang