I only have one, and it's for a rather niche use: fixing incorrect or missing h264/h265 bitstream metadata without re-encoding, for example:

    ffmpeg -i source.avc -c copy -bsf:v h264_metadata=colour_primaries=1:matrix_coefficients=1 output.h264

https://ffmpeg.org/ffmpeg-bitstream-filters.html#h264_005fme... https://www.itu.int/rec/T-REC-H.264-201906-I/en