test0r
37c0e720fc
The static SET_FORMAT_OF_OUTPUT_ONCE flag pinned the OUTPUT format to the first call's dimensions, which for mpv's probe pattern means 128x128. Subsequent CreateSurfaces2 for the real 1920x1088 resolution would then read CAPTURE format from the kernel (which derives from the OUTPUT format) and get 128x128 sizes back — leading to a VADRMPRIMESurfaceDescriptor with width=1920 height=1088 but pitch=128 offset=16384. Mesa's WSI rejected this as 'pitch too small,' and the mpv vaapi --vo=gpu render landed on a solid blue frame. Same root cause for Firefox 150's SW fallback after frame 0. Replace SET_FORMAT_OF_OUTPUT_ONCE with LAST_OUTPUT_WIDTH/HEIGHT tracking. When dimensions change, call REQBUFS(0) on OUTPUT to drop any stale buffers (S_FMT is rejected by V4L2 while buffers exist), then re-S_FMT at the new resolution. The kernel will derive the new CAPTURE format from this OUTPUT format on the next CreateBufs + G_FMT cycle. Caveat (TODO for next iteration): for consumers that legitimately stream multiple resolutions in sequence (mid-stream resolution change via V4L2_EVENT_SOURCE_CHANGE), the current approach still requires CreateSurfaces2 to be called, which mpv does on probe. A proper context-level redesign would handle SOURCE_CHANGE inline with STREAMOFF + REQBUFS(0) + new S_FMT. Diagnosis and root cause: surfaced by 2026-05-04 Phase 5 sonnet review (finding 7.3) as a 'latent bug to document.' Today's instrumentation captured it as the active bug — the ExportSurfaceHandle dump showed pitch=128 for 1920x1088 surfaces right before MESA reported 'WSI pitch too small' and dropped to software. 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.