[FFmpeg-devel] [PATCH v2] rtpdec: Fix RTP timestamp wraparound in Producer Reference Time

[FFmpeg-devel] [PATCH v2] rtpdec: Fix RTP timestamp wraparound in Producer Reference Time

[Clément Péron]

The rtp_set_prft() function incorrectly calculates the timestamp delta
when RTP timestamps wrap around the 32-bit boundary. The current code:

    delta_timestamp = (int64_t)timestamp - (int64_t)s->last_rtcp_timestamp;

treats both timestamps as large positive values, causing wraparound to
produce a large negative delta instead of the correct small positive delta.

For example, with a 90kHz video clock:
- last_rtcp_timestamp = 0xFFFFFF00 (near wraparound)
- timestamp = 0x00000100 (after wraparound)
- Current result: delta ≈ -4.3 billion ticks ≈ -47,721 seconds
- Expected result: delta ≈ +512 ticks ≈ +0.006 seconds

This causes prft->wallclock to jump backward by approximately:
- 90kHz video: ~47,721 seconds (~13.25 hours)
- 48kHz audio: ~89,478 seconds (~24.9 hours)
- 8kHz audio: ~536,871 seconds (~6.2 days)

Fix by casting the subtraction result to int32_t, which correctly
handles wraparound through modular arithmetic:

    delta_timestamp = (int32_t)(timestamp - s->last_rtcp_timestamp);

This ensures the delta is always in the range [-2^31, 2^31-1], making
wraparound produce the correct small positive values.

Fixes timing jumps in applications that rely on Producer Reference Time
for media synchronization.

Signed-off-by: Clément Péron <peron.clem@gmail.com>
---
 libavformat/rtpdec.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/libavformat/rtpdec.c b/libavformat/rtpdec.c
index 729bf83685..7664ab58bd 100644
--- a/libavformat/rtpdec.c
+++ b/libavformat/rtpdec.c
@@ -633,7 +633,8 @@ void ff_rtp_parse_set_crypto(RTPDemuxContext *s, const char *suite,
 }
 
 static int rtp_set_prft(RTPDemuxContext *s, AVPacket *pkt, uint32_t timestamp) {
-    int64_t rtcp_time, delta_timestamp, delta_time;
+    int64_t rtcp_time, delta_time;
+    int32_t delta_timestamp;
 
     AVProducerReferenceTime *prft =
         (AVProducerReferenceTime *) av_packet_new_side_data(
@@ -642,7 +643,7 @@ static int rtp_set_prft(RTPDemuxContext *s, AVPacket *pkt, uint32_t timestamp) {
         return AVERROR(ENOMEM);
 
     rtcp_time = ff_parse_ntp_time(s->last_rtcp_ntp_time) - NTP_OFFSET_US;
-    delta_timestamp = (int64_t)timestamp - (int64_t)s->last_rtcp_timestamp;
+    delta_timestamp = (int32_t)(timestamp - s->last_rtcp_timestamp);
     delta_time = av_rescale_q(delta_timestamp, s->st->time_base, AV_TIME_BASE_Q);
 
     prft->wallclock = rtcp_time + delta_time;
-- 
2.48.1

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Re: [FFmpeg-devel] [PATCH v2] rtpdec: Fix RTP timestamp wraparound in Producer Reference Time

[Michael Niedermayer]

[-- Attachment #1.1: Type: text/plain, Size: 2869 bytes --]

Hi

On Sat, Jun 07, 2025 at 10:06:19AM +0200, Clément Péron wrote:
> The rtp_set_prft() function incorrectly calculates the timestamp delta
> when RTP timestamps wrap around the 32-bit boundary. The current code:
> 
>     delta_timestamp = (int64_t)timestamp - (int64_t)s->last_rtcp_timestamp;
> 
> treats both timestamps as large positive values, causing wraparound to
> produce a large negative delta instead of the correct small positive delta.
> 
> For example, with a 90kHz video clock:
> - last_rtcp_timestamp = 0xFFFFFF00 (near wraparound)
> - timestamp = 0x00000100 (after wraparound)
> - Current result: delta ≈ -4.3 billion ticks ≈ -47,721 seconds
> - Expected result: delta ≈ +512 ticks ≈ +0.006 seconds
> 
> This causes prft->wallclock to jump backward by approximately:
> - 90kHz video: ~47,721 seconds (~13.25 hours)
> - 48kHz audio: ~89,478 seconds (~24.9 hours)
> - 8kHz audio: ~536,871 seconds (~6.2 days)
> 
> Fix by casting the subtraction result to int32_t, which correctly
> handles wraparound through modular arithmetic:
> 
>     delta_timestamp = (int32_t)(timestamp - s->last_rtcp_timestamp);
> 
> This ensures the delta is always in the range [-2^31, 2^31-1], making
> wraparound produce the correct small positive values.
> 
> Fixes timing jumps in applications that rely on Producer Reference Time
> for media synchronization.
> 
> Signed-off-by: Clément Péron <peron.clem@gmail.com>
> ---
>  libavformat/rtpdec.c | 5 +++--
>  1 file changed, 3 insertions(+), 2 deletions(-)
> 
> diff --git a/libavformat/rtpdec.c b/libavformat/rtpdec.c
> index 729bf83685..7664ab58bd 100644
> --- a/libavformat/rtpdec.c
> +++ b/libavformat/rtpdec.c
> @@ -633,7 +633,8 @@ void ff_rtp_parse_set_crypto(RTPDemuxContext *s, const char *suite,
>  }
>  
>  static int rtp_set_prft(RTPDemuxContext *s, AVPacket *pkt, uint32_t timestamp) {
> -    int64_t rtcp_time, delta_timestamp, delta_time;
> +    int64_t rtcp_time, delta_time;
> +    int32_t delta_timestamp;
>  
>      AVProducerReferenceTime *prft =
>          (AVProducerReferenceTime *) av_packet_new_side_data(
> @@ -642,7 +643,7 @@ static int rtp_set_prft(RTPDemuxContext *s, AVPacket *pkt, uint32_t timestamp) {
>          return AVERROR(ENOMEM);
>  
>      rtcp_time = ff_parse_ntp_time(s->last_rtcp_ntp_time) - NTP_OFFSET_US;
> -    delta_timestamp = (int64_t)timestamp - (int64_t)s->last_rtcp_timestamp;
> +    delta_timestamp = (int32_t)(timestamp - s->last_rtcp_timestamp);
>      delta_time = av_rescale_q(delta_timestamp, s->st->time_base, AV_TIME_BASE_Q);
>  
>      prft->wallclock = rtcp_time + delta_time;

will apply

thx

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

Asymptotically faster algorithms should always be preferred if you have
asymptotical amounts of data

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Re: [FFmpeg-devel] [PATCH v2] rtpdec: Fix RTP timestamp wraparound in Producer Reference Time

[Clément Péron]

Hi,

On Sun, 8 Jun 2025 at 01:33, Michael Niedermayer <michael@niedermayer.cc> wrote:
>
> Hi
>
> On Sat, Jun 07, 2025 at 10:06:19AM +0200, Clément Péron wrote:
> > The rtp_set_prft() function incorrectly calculates the timestamp delta
> > when RTP timestamps wrap around the 32-bit boundary. The current code:
> >
> >     delta_timestamp = (int64_t)timestamp - (int64_t)s->last_rtcp_timestamp;
> >
> > treats both timestamps as large positive values, causing wraparound to
> > produce a large negative delta instead of the correct small positive delta.
> >
> > For example, with a 90kHz video clock:
> > - last_rtcp_timestamp = 0xFFFFFF00 (near wraparound)
> > - timestamp = 0x00000100 (after wraparound)
> > - Current result: delta ≈ -4.3 billion ticks ≈ -47,721 seconds
> > - Expected result: delta ≈ +512 ticks ≈ +0.006 seconds
> >
> > This causes prft->wallclock to jump backward by approximately:
> > - 90kHz video: ~47,721 seconds (~13.25 hours)
> > - 48kHz audio: ~89,478 seconds (~24.9 hours)
> > - 8kHz audio: ~536,871 seconds (~6.2 days)
> >
> > Fix by casting the subtraction result to int32_t, which correctly
> > handles wraparound through modular arithmetic:
> >
> >     delta_timestamp = (int32_t)(timestamp - s->last_rtcp_timestamp);
> >
> > This ensures the delta is always in the range [-2^31, 2^31-1], making
> > wraparound produce the correct small positive values.
> >
> > Fixes timing jumps in applications that rely on Producer Reference Time
> > for media synchronization.
> >
> > Signed-off-by: Clément Péron <peron.clem@gmail.com>
> > ---
> >  libavformat/rtpdec.c | 5 +++--
> >  1 file changed, 3 insertions(+), 2 deletions(-)
> >
> > diff --git a/libavformat/rtpdec.c b/libavformat/rtpdec.c
> > index 729bf83685..7664ab58bd 100644
> > --- a/libavformat/rtpdec.c
> > +++ b/libavformat/rtpdec.c
> > @@ -633,7 +633,8 @@ void ff_rtp_parse_set_crypto(RTPDemuxContext *s, const char *suite,
> >  }
> >
> >  static int rtp_set_prft(RTPDemuxContext *s, AVPacket *pkt, uint32_t timestamp) {
> > -    int64_t rtcp_time, delta_timestamp, delta_time;
> > +    int64_t rtcp_time, delta_time;
> > +    int32_t delta_timestamp;
> >
> >      AVProducerReferenceTime *prft =
> >          (AVProducerReferenceTime *) av_packet_new_side_data(
> > @@ -642,7 +643,7 @@ static int rtp_set_prft(RTPDemuxContext *s, AVPacket *pkt, uint32_t timestamp) {
> >          return AVERROR(ENOMEM);
> >
> >      rtcp_time = ff_parse_ntp_time(s->last_rtcp_ntp_time) - NTP_OFFSET_US;
> > -    delta_timestamp = (int64_t)timestamp - (int64_t)s->last_rtcp_timestamp;
> > +    delta_timestamp = (int32_t)(timestamp - s->last_rtcp_timestamp);
> >      delta_time = av_rescale_q(delta_timestamp, s->st->time_base, AV_TIME_BASE_Q);
> >
> >      prft->wallclock = rtcp_time + delta_time;
>
> will apply

Thank you

I found also another place where this rollover could be problematic

diff --git a/libavformat/rtpdec.c b/libavformat/rtpdec.c
index 7664ab58bd..aa1ea46469 100644
--- a/libavformat/rtpdec.c
+++ b/libavformat/rtpdec.c
@@ -670,10 +670,10 @@ static void finalize_packet(RTPDemuxContext *s,
AVPacket *pkt, uint32_t timestam

     if (s->last_rtcp_ntp_time != AV_NOPTS_VALUE && s->ic->nb_streams > 1) {
         int64_t addend;
-        int delta_timestamp;
+        int32_t delta_timestamp;

         /* compute pts from timestamp with received ntp_time */
-        delta_timestamp = timestamp - s->last_rtcp_timestamp;
+        delta_timestamp = (int32_t)(timestamp - s->last_rtcp_timestamp);
         /* convert to the PTS timebase */
         addend = av_rescale(s->last_rtcp_ntp_time - s->first_rtcp_ntp_time,
                             s->st->time_base.den,

But to be honest I don't have time to properly test it, but I could
send a patch with an RFT tag if you want.

Regards,


>
> thx
>
> [...]
> --
> Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB
>
> Asymptotically faster algorithms should always be preferred if you have
> asymptotical amounts of data
> _______________________________________________
> ffmpeg-devel mailing list
> ffmpeg-devel@ffmpeg.org
> https://ffmpeg.org/mailman/listinfo/ffmpeg-devel
>
> To unsubscribe, visit link above, or email
> ffmpeg-devel-request@ffmpeg.org with subject "unsubscribe".
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Re: [FFmpeg-devel] [PATCH v2] rtpdec: Fix RTP timestamp wraparound in Producer Reference Time

[Michael Niedermayer]

[-- Attachment #1.1: Type: text/plain, Size: 4589 bytes --]

On Sun, Jun 08, 2025 at 09:27:07AM +0200, Clément Péron wrote:
> Hi,
> 
> On Sun, 8 Jun 2025 at 01:33, Michael Niedermayer <michael@niedermayer.cc> wrote:
> >
> > Hi
> >
> > On Sat, Jun 07, 2025 at 10:06:19AM +0200, Clément Péron wrote:
> > > The rtp_set_prft() function incorrectly calculates the timestamp delta
> > > when RTP timestamps wrap around the 32-bit boundary. The current code:
> > >
> > >     delta_timestamp = (int64_t)timestamp - (int64_t)s->last_rtcp_timestamp;
> > >
> > > treats both timestamps as large positive values, causing wraparound to
> > > produce a large negative delta instead of the correct small positive delta.
> > >
> > > For example, with a 90kHz video clock:
> > > - last_rtcp_timestamp = 0xFFFFFF00 (near wraparound)
> > > - timestamp = 0x00000100 (after wraparound)
> > > - Current result: delta ≈ -4.3 billion ticks ≈ -47,721 seconds
> > > - Expected result: delta ≈ +512 ticks ≈ +0.006 seconds
> > >
> > > This causes prft->wallclock to jump backward by approximately:
> > > - 90kHz video: ~47,721 seconds (~13.25 hours)
> > > - 48kHz audio: ~89,478 seconds (~24.9 hours)
> > > - 8kHz audio: ~536,871 seconds (~6.2 days)
> > >
> > > Fix by casting the subtraction result to int32_t, which correctly
> > > handles wraparound through modular arithmetic:
> > >
> > >     delta_timestamp = (int32_t)(timestamp - s->last_rtcp_timestamp);
> > >
> > > This ensures the delta is always in the range [-2^31, 2^31-1], making
> > > wraparound produce the correct small positive values.
> > >
> > > Fixes timing jumps in applications that rely on Producer Reference Time
> > > for media synchronization.
> > >
> > > Signed-off-by: Clément Péron <peron.clem@gmail.com>
> > > ---
> > >  libavformat/rtpdec.c | 5 +++--
> > >  1 file changed, 3 insertions(+), 2 deletions(-)
> > >
> > > diff --git a/libavformat/rtpdec.c b/libavformat/rtpdec.c
> > > index 729bf83685..7664ab58bd 100644
> > > --- a/libavformat/rtpdec.c
> > > +++ b/libavformat/rtpdec.c
> > > @@ -633,7 +633,8 @@ void ff_rtp_parse_set_crypto(RTPDemuxContext *s, const char *suite,
> > >  }
> > >
> > >  static int rtp_set_prft(RTPDemuxContext *s, AVPacket *pkt, uint32_t timestamp) {
> > > -    int64_t rtcp_time, delta_timestamp, delta_time;
> > > +    int64_t rtcp_time, delta_time;
> > > +    int32_t delta_timestamp;
> > >
> > >      AVProducerReferenceTime *prft =
> > >          (AVProducerReferenceTime *) av_packet_new_side_data(
> > > @@ -642,7 +643,7 @@ static int rtp_set_prft(RTPDemuxContext *s, AVPacket *pkt, uint32_t timestamp) {
> > >          return AVERROR(ENOMEM);
> > >
> > >      rtcp_time = ff_parse_ntp_time(s->last_rtcp_ntp_time) - NTP_OFFSET_US;
> > > -    delta_timestamp = (int64_t)timestamp - (int64_t)s->last_rtcp_timestamp;
> > > +    delta_timestamp = (int32_t)(timestamp - s->last_rtcp_timestamp);
> > >      delta_time = av_rescale_q(delta_timestamp, s->st->time_base, AV_TIME_BASE_Q);
> > >
> > >      prft->wallclock = rtcp_time + delta_time;
> >
> > will apply
> 
> Thank you
> 
> I found also another place where this rollover could be problematic
> 
> diff --git a/libavformat/rtpdec.c b/libavformat/rtpdec.c
> index 7664ab58bd..aa1ea46469 100644
> --- a/libavformat/rtpdec.c
> +++ b/libavformat/rtpdec.c
> @@ -670,10 +670,10 @@ static void finalize_packet(RTPDemuxContext *s,
> AVPacket *pkt, uint32_t timestam
> 
>      if (s->last_rtcp_ntp_time != AV_NOPTS_VALUE && s->ic->nb_streams > 1) {
>          int64_t addend;
> -        int delta_timestamp;
> +        int32_t delta_timestamp;
> 
>          /* compute pts from timestamp with received ntp_time */
> -        delta_timestamp = timestamp - s->last_rtcp_timestamp;
> +        delta_timestamp = (int32_t)(timestamp - s->last_rtcp_timestamp);
>          /* convert to the PTS timebase */
>          addend = av_rescale(s->last_rtcp_ntp_time - s->first_rtcp_ntp_time,
>                              s->st->time_base.den,
> 
> But to be honest I don't have time to properly test it, but I could
> send a patch with an RFT tag if you want.

better to have a patch than no patch, also this only affects 64bit int
systems. I would tend to apply this fix even if noone tests it.
Or am i missing something ? Its just more correct after the patch

thx

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

The difference between a dictatorship and a democracy is that every 4 years
the population together is allowed to provide 1 bit of input to the government.

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Re: [FFmpeg-devel] [PATCH v2] rtpdec: Fix RTP timestamp wraparound in Producer Reference Time

[Clément Péron]

On Sun, 8 Jun 2025 at 22:09, Michael Niedermayer <michael@niedermayer.cc> wrote:
>
> On Sun, Jun 08, 2025 at 09:27:07AM +0200, Clément Péron wrote:
> > Hi,
> >
> > On Sun, 8 Jun 2025 at 01:33, Michael Niedermayer <michael@niedermayer.cc> wrote:
> > >
> > > Hi
> > >
> > > On Sat, Jun 07, 2025 at 10:06:19AM +0200, Clément Péron wrote:
> > > > The rtp_set_prft() function incorrectly calculates the timestamp delta
> > > > when RTP timestamps wrap around the 32-bit boundary. The current code:
> > > >
> > > >     delta_timestamp = (int64_t)timestamp - (int64_t)s->last_rtcp_timestamp;
> > > >
> > > > treats both timestamps as large positive values, causing wraparound to
> > > > produce a large negative delta instead of the correct small positive delta.
> > > >
> > > > For example, with a 90kHz video clock:
> > > > - last_rtcp_timestamp = 0xFFFFFF00 (near wraparound)
> > > > - timestamp = 0x00000100 (after wraparound)
> > > > - Current result: delta ≈ -4.3 billion ticks ≈ -47,721 seconds
> > > > - Expected result: delta ≈ +512 ticks ≈ +0.006 seconds
> > > >
> > > > This causes prft->wallclock to jump backward by approximately:
> > > > - 90kHz video: ~47,721 seconds (~13.25 hours)
> > > > - 48kHz audio: ~89,478 seconds (~24.9 hours)
> > > > - 8kHz audio: ~536,871 seconds (~6.2 days)
> > > >
> > > > Fix by casting the subtraction result to int32_t, which correctly
> > > > handles wraparound through modular arithmetic:
> > > >
> > > >     delta_timestamp = (int32_t)(timestamp - s->last_rtcp_timestamp);
> > > >
> > > > This ensures the delta is always in the range [-2^31, 2^31-1], making
> > > > wraparound produce the correct small positive values.
> > > >
> > > > Fixes timing jumps in applications that rely on Producer Reference Time
> > > > for media synchronization.
> > > >
> > > > Signed-off-by: Clément Péron <peron.clem@gmail.com>
> > > > ---
> > > >  libavformat/rtpdec.c | 5 +++--
> > > >  1 file changed, 3 insertions(+), 2 deletions(-)
> > > >
> > > > diff --git a/libavformat/rtpdec.c b/libavformat/rtpdec.c
> > > > index 729bf83685..7664ab58bd 100644
> > > > --- a/libavformat/rtpdec.c
> > > > +++ b/libavformat/rtpdec.c
> > > > @@ -633,7 +633,8 @@ void ff_rtp_parse_set_crypto(RTPDemuxContext *s, const char *suite,
> > > >  }
> > > >
> > > >  static int rtp_set_prft(RTPDemuxContext *s, AVPacket *pkt, uint32_t timestamp) {
> > > > -    int64_t rtcp_time, delta_timestamp, delta_time;
> > > > +    int64_t rtcp_time, delta_time;
> > > > +    int32_t delta_timestamp;
> > > >
> > > >      AVProducerReferenceTime *prft =
> > > >          (AVProducerReferenceTime *) av_packet_new_side_data(
> > > > @@ -642,7 +643,7 @@ static int rtp_set_prft(RTPDemuxContext *s, AVPacket *pkt, uint32_t timestamp) {
> > > >          return AVERROR(ENOMEM);
> > > >
> > > >      rtcp_time = ff_parse_ntp_time(s->last_rtcp_ntp_time) - NTP_OFFSET_US;
> > > > -    delta_timestamp = (int64_t)timestamp - (int64_t)s->last_rtcp_timestamp;
> > > > +    delta_timestamp = (int32_t)(timestamp - s->last_rtcp_timestamp);
> > > >      delta_time = av_rescale_q(delta_timestamp, s->st->time_base, AV_TIME_BASE_Q);
> > > >
> > > >      prft->wallclock = rtcp_time + delta_time;
> > >
> > > will apply
> >
> > Thank you
> >
> > I found also another place where this rollover could be problematic
> >
> > diff --git a/libavformat/rtpdec.c b/libavformat/rtpdec.c
> > index 7664ab58bd..aa1ea46469 100644
> > --- a/libavformat/rtpdec.c
> > +++ b/libavformat/rtpdec.c
> > @@ -670,10 +670,10 @@ static void finalize_packet(RTPDemuxContext *s,
> > AVPacket *pkt, uint32_t timestam
> >
> >      if (s->last_rtcp_ntp_time != AV_NOPTS_VALUE && s->ic->nb_streams > 1) {
> >          int64_t addend;
> > -        int delta_timestamp;
> > +        int32_t delta_timestamp;
> >
> >          /* compute pts from timestamp with received ntp_time */
> > -        delta_timestamp = timestamp - s->last_rtcp_timestamp;
> > +        delta_timestamp = (int32_t)(timestamp - s->last_rtcp_timestamp);
> >          /* convert to the PTS timebase */
> >          addend = av_rescale(s->last_rtcp_ntp_time - s->first_rtcp_ntp_time,
> >                              s->st->time_base.den,
> >
> > But to be honest I don't have time to properly test it, but I could
> > send a patch with an RFT tag if you want.
>
> better to have a patch than no patch, also this only affects 64bit int
> systems. I would tend to apply this fix even if noone tests it.
> Or am i missing something ? Its just more correct after the patch

You're correct I have sent another patch + add comment regarding
Kieran feedback.

https://patchwork.ffmpeg.org/project/ffmpeg/patch/20250608150737.73929-1-peron.clem@gmail.com/


>
> thx
>
> [...]
> --
> Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB
>
> The difference between a dictatorship and a democracy is that every 4 years
> the population together is allowed to provide 1 bit of input to the government.
> _______________________________________________
> ffmpeg-devel mailing list
> ffmpeg-devel@ffmpeg.org
> https://ffmpeg.org/mailman/listinfo/ffmpeg-devel
>
> To unsubscribe, visit link above, or email
> ffmpeg-devel-request@ffmpeg.org with subject "unsubscribe".
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Re: [FFmpeg-devel] [PATCH v2] rtpdec: Fix RTP timestamp wraparound in Producer Reference Time

[Kieran Kunhya via ffmpeg-devel]

On Sat, Jun 7, 2025 at 9:06 AM Clément Péron
<peron.clem-at-gmail.com@ffmpeg.org> wrote:
>
> The rtp_set_prft() function incorrectly calculates the timestamp delta
> when RTP timestamps wrap around the 32-bit boundary. The current code:
>
>     delta_timestamp = (int64_t)timestamp - (int64_t)s->last_rtcp_timestamp;
>
> treats both timestamps as large positive values, causing wraparound to
> produce a large negative delta instead of the correct small positive delta.
>
> For example, with a 90kHz video clock:
> - last_rtcp_timestamp = 0xFFFFFF00 (near wraparound)
> - timestamp = 0x00000100 (after wraparound)
> - Current result: delta ≈ -4.3 billion ticks ≈ -47,721 seconds
> - Expected result: delta ≈ +512 ticks ≈ +0.006 seconds
>
> This causes prft->wallclock to jump backward by approximately:
> - 90kHz video: ~47,721 seconds (~13.25 hours)
> - 48kHz audio: ~89,478 seconds (~24.9 hours)
> - 8kHz audio: ~536,871 seconds (~6.2 days)
>
> Fix by casting the subtraction result to int32_t, which correctly
> handles wraparound through modular arithmetic:
>
>     delta_timestamp = (int32_t)(timestamp - s->last_rtcp_timestamp);
>
> This ensures the delta is always in the range [-2^31, 2^31-1], making
> wraparound produce the correct small positive values.
>
> Fixes timing jumps in applications that rely on Producer Reference Time
> for media synchronization.
>
> Signed-off-by: Clément Péron <peron.clem@gmail.com>
> ---
>  libavformat/rtpdec.c | 5 +++--
>  1 file changed, 3 insertions(+), 2 deletions(-)
>
> diff --git a/libavformat/rtpdec.c b/libavformat/rtpdec.c
> index 729bf83685..7664ab58bd 100644
> --- a/libavformat/rtpdec.c
> +++ b/libavformat/rtpdec.c
> @@ -633,7 +633,8 @@ void ff_rtp_parse_set_crypto(RTPDemuxContext *s, const char *suite,
>  }
>
>  static int rtp_set_prft(RTPDemuxContext *s, AVPacket *pkt, uint32_t timestamp) {
> -    int64_t rtcp_time, delta_timestamp, delta_time;
> +    int64_t rtcp_time, delta_time;
> +    int32_t delta_timestamp;
>
>      AVProducerReferenceTime *prft =
>          (AVProducerReferenceTime *) av_packet_new_side_data(
> @@ -642,7 +643,7 @@ static int rtp_set_prft(RTPDemuxContext *s, AVPacket *pkt, uint32_t timestamp) {
>          return AVERROR(ENOMEM);
>
>      rtcp_time = ff_parse_ntp_time(s->last_rtcp_ntp_time) - NTP_OFFSET_US;
> -    delta_timestamp = (int64_t)timestamp - (int64_t)s->last_rtcp_timestamp;
> +    delta_timestamp = (int32_t)(timestamp - s->last_rtcp_timestamp);
>      delta_time = av_rescale_q(delta_timestamp, s->st->time_base, AV_TIME_BASE_Q);
>
>      prft->wallclock = rtcp_time + delta_time;
> --
> 2.48.1

Seems fine, a comment might help explain the wrapround logic.

Kieran
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