This is what Nicholas George, one of the maintainers of ffmpeg said about these errors over 10 years ago:
The warning says that the packets or time may be invalid, not that they
actually will be.It seems that your setting does not actually need the information found by
the parser. For PCM, that could be expected. For ffv1, I guess there are no
B-frames.This warning seemed like a good idea at the time, but now I realize that
there are lots of codecs that work fine without a parser even if the format
thinks it needs one. I will think about it some more.In the meantime, just ignore the warning: if it works, then it means it was
harmless.
A similar query (with a possible solution) was documented in this thread:
Also, are your original sources Variable Frame Rate (VFR)? If so have you tried converting them to edit-friendly first?