AAC-LC RTP Multicast bug

[AJ]

After 8-10 hours of AAC-LC stereo audio RTP Multicast streaming ok, the stream changes to continuously output silence or distorted low level audio (sometimes with audio in one channel only). It requires a restart of FFMPEG to resolve, but then always the problem occurs another 8-10 hours later.

It occurs with AAC-LC whether using the native AAC encoder or libFDK_AAC. It does not occur with Opus or HE-AAC.

96 kbps 32 kHz. Windows 11.

ffmpeg -re -f s16le -ar 32000 -ac 2 -i pipe:0 -af "lowpass=f=16000, volume=-2dB" -c:a libfdk_aac -profile:a aac_low -flags +global_header -b:a 96k -pkt_size 1480 -f rtp -payload_type 96 rtp://225.0.0.20:6004 -async 2000

[AJ]

More info/clues on this bug for the developers.

1. From starting FFmpeg, it seems to always be 9h17m till the audio in the stream breaks. Easy to replicate.

2. @~9h17m, it starts gradually degrading the stereo audio over the course of about 60-120s, after which it remains either a silent stream (at the correct bit rate), or low level and highly distorted audio. Sometimes one channel does this a minute or two before the 2nd channel does the same.

3. Changing -pkt_size to a higher value (5000), reducing the packet count, makes no difference to the 9h17m time to fault.

On the same pc, other instances have been test streaming HE-AAC & Opus streams 24/7 for 2+ weeks now without any issue. Just impacting both AAC-LC codecs (internal & FDK). Our application needs a AAC family codec @ ~100 kbps, and we'd prefer to use AAC-LC than HE-AAC.

Thank you for this useful tool.