[FFmpeg-devel] [PATCH] avformat/mpegtsenc: Limit TS invalid messages

[FFmpeg-devel] [PATCH] avformat/mpegtsenc: Limit TS invalid messages

[David Dominguez via ffmpeg-devel]

mpegts_write_pes() warns when DTS - PCR is negative. This is
done to detect frames that are late for decoding, meaning that
timestamping is wrong or the muxrate value is insufficient.

But this comparison only makes sense on the first packet of
the frame. After that the comparison will always be negative
as DTS doesn't change until the next frame, resulting in
hundreds of useless warnings.

Addtionaly, for long key frames that take several frame periods
to transmity false warnings may be issued if max_delay
is low enough. For example, in low latency CC video.

Limiting the warning to the start of frame transmission fixes
these issues.

Signed-off-by: David Dominguez <ddominguez@fagormultimedia.com>
---
 libavformat/mpegtsenc.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/libavformat/mpegtsenc.c b/libavformat/mpegtsenc.c
index 6935b71cfe..d66055e1dc 100644
--- a/libavformat/mpegtsenc.c
+++ b/libavformat/mpegtsenc.c
@@ -1596,7 +1596,7 @@ static void mpegts_write_pes(AVFormatContext *s, AVStream *st,
             set_af_flag(buf, 0x10);
             q = get_ts_payload_start(buf);
             // add 11, pcr references the last byte of program clock reference base
-            if (dts != AV_NOPTS_VALUE && dts < pcr / SYSTEM_CLOCK_FREQUENCY_DIVISOR)
+            if (is_start && dts != AV_NOPTS_VALUE && dts < pcr / SYSTEM_CLOCK_FREQUENCY_DIVISOR)
                 av_log(s, AV_LOG_WARNING, "dts < pcr, TS is invalid\n");
             extend_af(buf, write_pcr_bits(q, pcr));
             q = get_ts_payload_start(buf);
-- 
2.34.1

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[FFmpeg-devel] Re: [PATCH] avformat/mpegtsenc: Limit TS invalid messages

[Michael Niedermayer via ffmpeg-devel]

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Hi

On Thu, Oct 02, 2025 at 11:36:33PM +0200, David Dominguez via ffmpeg-devel wrote:
> mpegts_write_pes() warns when DTS - PCR is negative. This is
> done to detect frames that are late for decoding, meaning that
> timestamping is wrong or the muxrate value is insufficient.
> 
> But this comparison only makes sense on the first packet of
> the frame. After that the comparison will always be negative
> as DTS doesn't change until the next frame, resulting in
> hundreds of useless warnings.
> 
> Addtionaly, for long key frames that take several frame periods
> to transmity false warnings may be issued if max_delay
> is low enough. For example, in low latency CC video.
> 
> Limiting the warning to the start of frame transmission fixes
> these issues.

This doesnt feel right, the time a frame is decoded has
to be after all of its parts are transmitted
But there are other people here, who know mpeg-ts much better than i
do

thx

[...]
-- 
Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

The worst form of inequality is to try to make unequal things equal.
-- Aristotle

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[FFmpeg-devel] Re: [PATCH] avformat/mpegtsenc: Limit TS invalid messages

[Kieran Kunhya via ffmpeg-devel]

On Mon, 6 Oct 2025, 04:46 Michael Niedermayer via ffmpeg-devel, <
ffmpeg-devel@ffmpeg.org> wrote:

> Hi
>
> On Thu, Oct 02, 2025 at 11:36:33PM +0200, David Dominguez via ffmpeg-devel
> wrote:
> > mpegts_write_pes() warns when DTS - PCR is negative. This is
> > done to detect frames that are late for decoding, meaning that
> > timestamping is wrong or the muxrate value is insufficient.
> >
> > But this comparison only makes sense on the first packet of
> > the frame. After that the comparison will always be negative
> > as DTS doesn't change until the next frame, resulting in
> > hundreds of useless warnings.
> >
> > Addtionaly, for long key frames that take several frame periods
> > to transmity false warnings may be issued if max_delay
> > is low enough. For example, in low latency CC video.
> >
> > Limiting the warning to the start of frame transmission fixes
> > these issues.
>
> This doesnt feel right, the time a frame is decoded has
> to be after all of its parts are transmitted


In TS, yes. This patch makes no sense.

Kieran

>
>
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