ffmpeg -y -hwaccel vaapi -vaapi_device /dev/dri/renderD128 -hwaccel_output_format vaapi -i a.mp4 -frames 600 -c:v mpeg2_vaapi -b:v 10000k -minrate:v 10000k -maxrate:v 10000k -compression_level 4 -g 24 -bf 2 out.mp4
returns:
Driver does not support some wanted packed headers (wanted 0x3, found 0x10). Assertion 0 && "Invalid RC mode." failed at libavcodec/vaapi_encode_mpeg2.c:545 Aborted (core dumped)
This seems to be an iHD driver issue - it does not support the required sequence and picture headers, so it cannot fill the extradata in a consistent way.
That is a limitation of MPEG-2 - it only supports a specific set of aspect ratios (see H.262 table 6-3).
Keep consistent with other codecs such as H264/HEVC.