[FFmpeg-trac] #7863(ffmpeg:new): prompeg FEC problem

[FFmpeg]

#7863: prompeg FEC problem
-------------------------------------+----------------------------------
             Reporter:  mpeg2tom     |                     Type:  defect
               Status:  new          |                 Priority:  normal
            Component:  ffmpeg       |                  Version:  4.1
             Keywords:  prompeg fec  |               Blocked By:
             Blocking:               |  Reproduced by developer:  0
Analyzed by developer:  0            |
-------------------------------------+----------------------------------
 Summary of the bug:
 rtp_mpegts with prompeg FEC has a problem, at least for L=5 D=20 - there
 are too many FEC packets, and some Column FEC payloads appear to be
 duplicates.
 How to reproduce:
 {{{
 $ ffmpeg -f lavfi -i testsrc=duration=30:size=1280x720:rate=30 -f
 rtp_mpegts -fec prompeg=l=5:d=20 rtp://239.0.0.1:5000
 ffmpeg version N-93595-gd7e8e62797 Copyright (c) 2000-2019 the FFmpeg
 developers
   built with gcc 7 (GCC)
   configuration:
   libavutil      56. 26.100 / 56. 26.100
   libavcodec     58. 51.100 / 58. 51.100
   libavformat    58. 27.102 / 58. 27.102
   libavdevice    58.  7.100 / 58.  7.100
   libavfilter     7. 48.100 /  7. 48.100
   libswscale      5.  4.100 /  5.  4.100
   libswresample   3.  4.100 /  3.  4.100
 }}}
 Capturing the output and using Wireshark Statistics/UDP Multicast Streams,
 you can see the output is:
 UDP DST 5000 – PT=33 (MPEG TS): 2507 packets, avg. 3.121 Mbps
 UDP DST 5001 – 2 (RTCP SR) packets, 223 kbps
 UDP DST 5002 – PT=96, Column FEC, 622 packets, avg. 784 kbps
 UDP DST 5004 – PT=96, Row FEC, 2507 packets, avg. 3.157 Mbps

 If L=5 and D=20, there should be 25 FEC packets for every 100 source
 packets (5 Column FEC & 20 Row FEC packets).  So for the 2507 source
 packets, there should be 125 Column FEC packets (but actually 622) and 500
 Row FEC packets (but actually 2507).

 I am also attaching Wireshark screenshots of example Column FEC packets
 with duplicated payloads and same SNBase low.

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Ticket URL: <https://trac.ffmpeg.org/ticket/7863>
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