I am using go2rtc to generate HLS streams to stream video from a PiCamera v3 running on an RPi5 for use in Octoprint.

I also need to copy and restream the HLS stream to an RTP Janus server for Spaghetti detection.

ffmpeg works fine on an HLS/TS (H264) stream but fails on a similar HLS/fMP4 (H264, H265, AAC) stream — however, for quality reasons, I would prefer to use an HLS/fMP4 stream.

Specifically, I am running the following:

ffmpeg -re -i <STREAM_URL> -an -c:v copy -an -f rtp rtp://127.0.0.1:17732?pkt_size=1300```

It streams properly forever when STREAM_URL is in HLS/TS format but fails when in HLS/fMP4 format after about 3-4 frames.

Running ffprobe gives the following:
HLS/TS:

  Duration: N/A, start: 0.000000, bitrate: N/A
  Program 0
    Metadata:
      variant_bitrate : 192000
  Stream #0:0: Video: h264 (High) ([27][0][0][0] / 0x001B), yuv420p(tv, bt709), 1536x864, 15 tbr, 90k tbn
    Metadata:
      variant_bitrate : 192000

HLS/fMP4:

  Duration: N/A, start: 0.000000, bitrate: 1248005 kb/s
  Program 0
    Metadata:
      variant_bitrate : 192000
  Stream #0:0: Video: h264 (High) (avc1 / 0x31637661), yuv420p(tv, bt709), 1536x864, 1248005 kb/s, 90k tbr, 90k tbn (default)
    Metadata:
      variant_bitrate : 192000
      major_brand     : iso5
      minor_version   : 512
      compatible_brands: iso5iso6mp41

• Why does ffmpeg succeed on a HLS/TS stream but fail on an HLS/fMP4 stream?
• Are there any parameters or simple envelope filters I can add to ffmpeg that will allow it to succeed on HLS/fMP4 streams, short of a computationally intensive re-transcoding?