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

[Devin Heitmueller]

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).

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

Devin

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