claude-noether
d7ef0f6cd9
Three more fixes after strace-diff localization vs kdirect. Fix 6 — fill_sequence ENABLE_SUPERRES: gate on picture->pic_info_fields.bits.use_superres instead of unconditional set-true. VAAPI doesn't expose enable_superres at sequence level; per strace diff kdirect clears the flag for streams not using superres (byte 1 of flags was the only SEQUENCE diff). After this fix, SEQUENCE ctrl byte-equal kdirect on every call. Fix 7 — refresh_frame_flags = 0xff (was 0): VAAPI doesn't expose refresh_frame_flags. Default 0xff = "refresh all DPB slots" matches kdirect's submission and AV1 spec default for KEY/SWITCH frames; for inter frames simple P-frame chains naturally tolerate this. Fix 8 — surface_object->av1_order_hint per-surface tracking. Set in av1_set_controls from picture->order_hint of the current frame. Also propagated to the linked display surface (when apply_grain=1 → cur_frame != cur_display) so future frames referencing the display surface find the order_hint via the linked_decode_surface_id. Tried + reverted: ref-name iteration of reference_frame_ts / order_hints via picture->ref_frame_idx[i-1] → DPB slot (Kwiboo's convention via FFmpeg's s->ref[i]). Empirically regressed 3/10 → 1/10. V4L2 uAPI's indexing here looks DPB-slot-direct despite the AV1 spec lexicon — needs kernel-side disambiguation to settle. Verification on ampere (av1_larger.ivf 352x288, 10 frames): Frames 0, 2, 4: PASS bit-exact (apply_grain=1, grain HW path) Frames 1, 3, 5-9: DIFF (apply_grain=0) 3/10 PASS (was 1/10 after iter checkpoint). test_av1.ivf 208x208: unchanged bit-exact PASS sha 029ee72c214b37c1 Remaining open: frame 1 (apply_grain=0, first inter) submits IDENTICAL FRAME ctrl bytes to kdirect (verified strace-diff post-fix), yet decoded output diverges. That means the divergence is no longer in control submission — points at OUTPUT-side bitstream differences between ffmpeg-vaapi and ffmpeg-v4l2request, or at DPB CAPTURE buffer state (grain-applied data being used as reference vs pre-grain). Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
v4l2-request libVA Backend
About
This libVA backend is designed to work with the Linux Video4Linux2 Request API that is used by a number of video codecs drivers, including the Video Engine found in most Allwinner SoCs.
Status
The v4l2-request libVA backend currently supports the following formats:
- MPEG2 (Simple and Main profiles)
- H264 (Baseline, Main and High profiles)
- H265 (Main profile)
Instructions
In order to use this libVA backend, the v4l2_request driver has to
be specified through the LIBVA_DRIVER_NAME environment variable, as
such:
export LIBVA_DRIVER_NAME=v4l2_request
A media player that supports VAAPI (such as VLC) can then be used to decode a video in a supported format:
vlc path/to/video.mpg
Sample media files can be obtained from:
http://samplemedia.linaro.org/MPEG2/
http://samplemedia.linaro.org/MPEG4/SVT/
Technical Notes
Surface
A Surface is an internal data structure never handled by the VA's user containing the output of a rendering. Usualy, a bunch of surfaces are created at the begining of decoding and they are then used alternatively. When created, a surface is assigned a corresponding v4l capture buffer and it is kept until the end of decoding. Syncing a surface waits for the v4l buffer to be available and then dequeue it.
Note: since a Surface is kept private from the VA's user, it can ask to directly render a Surface on screen in an X Drawable. Some kind of implementation is available in PutSurface but this is only for development purpose.
Context
A Context is a global data structure used for rendering a video of a certain format. When a context is created, input buffers are created and v4l's output (which is the compressed data input queue, since capture is the real output) format is set.
Picture
A Picture is an encoded input frame made of several buffers. A single input can contain slice data, headers and IQ matrix. Each Picture is assigned a request ID when created and each corresponding buffer might be turned into a v4l buffers or extended control when rendered. Finally they are submitted to kernel space when reaching EndPicture.
The real rendering is done in EndPicture instead of RenderPicture because the v4l2 driver expects to have the full corresponding extended control when a buffer is queued and we don't know in which order the different RenderPicture will be called.
Image
An Image is a standard data structure containing rendered frames in a usable pixel format. Here we only use NV12 buffers which are converted from sunxi's proprietary tiled pixel format with tiled_yuv when deriving an Image from a Surface.