ROOT CAUSE FIX for VP8 libva decode garbage output.
ffmpeg-vaapi's vaapi_vp8.c:191-192 STRIPS the VP8 uncompressed
header (3 bytes for interframe, 10 bytes for keyframe) before
submitting the slice data via VAAPI. ffmpeg-v4l2request (kdirect)
KEEPS the header in its OUTPUT buffer.
Hantro's rockchip_vpu2_vp8_dec_run (rockchip_vpu2_hw_vp8_dec.c:349)
hard-codes 'first_part_offset = V4L2_VP8_FRAME_IS_KEY_FRAME(hdr) ? 10 : 3'
as the byte offset into OUTPUT where the first compressed partition
starts. It uses this offset for:
- mb_offset_bits = first_part_offset * 8 + first_part_header_bits + 8
- dct_part_offset = first_part_offset + first_part_size
Without the header, every offset is wrong, the entropy decoder
spins on the wrong bytes, and every frame decodes to garbage.
Fix: in codec_store_buffer for VAProfileVP8Version0_3, prepend
header_size bytes (10 keyframe / 3 interframe) of zeros to OUTPUT
before the slice data memcpy. Hantro skips these bytes for actual
parsing (uses ctrl-struct values instead), so zero-fill is fine.
Empirical: iter33 kernel printk in vpu2_vp8_dec_run dumped the
v4l2_ctrl_vp8_frame struct for libva vs kdirect and confirmed
byte-identical control fields. Only the OUTPUT buffer bytes
differed, traced to ffmpeg-vaapi's header stripping.
claude-noether
7e0848d7d2