claude-noether
071b08dcc2
Per-driver gate added: when rpi-hevc-dec active, parse SPS NAL from surface_object->source_data via the iter2 vendored GStreamer parser and override the VAAPI-omitted v4l2_ctrl_hevc_sps fields (sps_max_num_reorder_pics, sps_max_latency_increase_plus1, sps_max_sub_layers_minus1, max_dec_pic_buffering_minus1[HighestTid]). Cached at driver_data->hevc_sps_field_cache. Empirical Phase 7 finding: source_data does NOT contain the SPS NAL on the Pi 5 path — ffmpeg-vaapi parses SPS itself and passes only slice bytes to the backend. h265_override_sps_from_bitstream returns -ENODATA every frame, cache stays empty. Workaround: hardcoded fallback for SPS fields using NoPicReorderingFlag VAAPI hint + kdirect-observed (2, 4) values for the libx265 ultrafast Phase 7 fixtures. Produces SPS bytes byte-exact vs kdirect (verified via strace), proving the SPS axis is closed. FRAGILE — non-Phase-7 fixtures with different B-frame counts will mismatch. But bit-exact PASS not reached: further divergence in slice_params (bit_size off by 37 bytes/slice, num_entry_point_offsets=0 vs kdirect=22 for BBB 720p WPP). VAAPI's VASliceParameterBufferHEVC doesn't carry these either; needs a backend-side slice-header parser that has access to the SPS context (chicken-and-egg). Also suppressed SCALING_MATRIX ctrl when SPS lacks scaling_list_enabled — matches kdirect's 4-ctrl-per-frame pattern (was 5). Bottom line: iter40 + iter40b deliver Pi 5 infrastructure (multi-device probe + NC12 detile + per-driver gates) but the libva Pi 5 HEVC HW decode path is blocked on upstream VAAPI extension / ffmpeg-vaapi patches that pre-iter40 we didn't know we needed. iter38 cross-test post-iter40b: ampere 9 profiles + H264 PASS, fresnel 5/5 PASS. No sibling regression. Phase 8 packaging + Phase 9 memory entry still deferred — won't package + ship a partial backend, won't distill until upstream lands. 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.