claude-noether
db0b7f9892
Root cause for Bug 5 (HEVC libva = all-zero CAPTURE) and Bug 4 (H.264 libva = keyframe partial), localized via iter17→iter24 kernel-printk chain: rkvdec_s_ctrl() for HEVC_SPS / H264_SPS calls get_image_fmt() and, if the resolved image_fmt differs from cached ctx->image_fmt (default RKVDEC_IMG_FMT_ANY at open), tries to reset the CAPTURE format. Format reset returns -EBUSY when vb2_is_busy(CAPTURE_queue) — any CAPTURE buffer allocated blocks the change. libva (iter5b-β) pre-allocates 24 CAPTURE buffers at CreateContext via cap_pool_init, BEFORE any per-frame S_EXT_CTRLS. First per-frame HEVC_SPS therefore fails with -EBUSY in try_or_set_cluster, breaks v4l2_ctrl_request_setup's outer loop, leaves all 5 staged HEVC compound controls at zero in ctx->ctrl_hdl. rkvdec_hevc_run reads zero (iter20 dmesg: sps[0..16]=00..00), hardware sees w=0 h=0, CAPTURE comes out all-zero (Bug 5). Fix: BEFORE cap_pool_init, inject one S_EXT_CTRLS (no request, no which) with a synthetic SPS containing the profile's known chroma + bit_depth. CAPTURE queue is still empty at this point → vb2_is_busy returns false → rkvdec_s_ctrl succeeds, ctx->image_fmt is updated to the profile's image_fmt. From then on, per-frame SPS submissions with matching chroma + bit_depth see image_fmt_changed=false → skip reset → commit succeeds. VP9 / MPEG-2 / VP8 paths are not affected: VP9's rkvdec coded_fmt_desc has no get_image_fmt op; MPEG-2 + VP8 route to hantro. Co-Authored-By: Claude Opus 4.7 (1M context) <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.