claude-noether
9037934b21
C1 vainfo PASS, C3 HW engagement PASS, C6 decode-correctness FAIL (V4L2_BUF_FLAG_ERROR on every CAPTURE DQBUF). Root cause empirically located: SPS sps_max_num_reorder_pics + sps_max_latency_increase_plus1 fields. Our backend uses a spec-legal fallback (sps_max_dec_pic_buffering_minus1, 0) because VAAPI doesn't forward these fields; rkvdec accepts it, rpi-hevc-dec validates against bitstream-true values and rejects. Real fix needs SPS NAL parse via the iter2 vendored GStreamer parser to populate bitstream-true values for the V4L2 SPS ctrl. Estimated 1 more 8(+1)-phase loop (iter40b). Phase 8 + Phase 9 deferred — won't package + deploy + ship a broken backend; won't distill lessons until the real fix lands. Sibling iter38 baseline NOT yet re-verified on fresnel + ampere post-iter40. Code paths gated on video_fd_rpi_hevc_dec >= 0 stay no-op on non-Pi hosts; only __arm__ → __aarch64__ guard change is globally observable but its is_10bit sub-gate stays dormant on 8-bit fixtures. Verify before declaring no-regression. 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.