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.

• It was caused by VA_ENC_PACKED_HEADER_SEQUENCE and VA_ENC_PACKED_HEADER_PICTURE can't be supported by iHD driver.
• Only VA_ENC_PACKED_HEADER_RAW_DATA can be supported.

That is a limitation of MPEG-2 - it only supports a specific set of aspect ratios (see H.262 table 6-3).

• If the ratio of the input stream is not on the list then it falls back to declaring that the stream has square pixels (and gives the warning to say it has done that).

Keep consistent with other codecs such as H264/HEVC.