Would you mind adding a ffmpeg plugin with the 4.4.x ffmpeg version as a alternative?
There's no info on your hardware/codecs/configuaration or Tvheadend configuration, and no debug logs .. ![]()
So assuming there is a real problem (not related to client-side drivers) the issue should be reported to Tvheadend devs so it can be investigated. If the problem is in Tvheadend (as you suggest) that's where a fix is required; we have no interest in packaging retro ffmpeg versions for workarounds.