libavformat/rtpdec: Fix RTP timestamp wraparound in Producer Reference Time

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>
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

0 files changed, 0 insertions, 0 deletions