test0r
74d8dd134a
Two empirically-validated correctness fixes from comparing our h264.c fill_dpb against FFmpeg's libavcodec/v4l2_request_h264.c::fill_dpb on the iter3 test rig (Firefox-fourier on ohm RK3568, bbb_1080p30 H.264): 1. Set dpb[].fields = V4L2_H264_FRAME_REF for every valid entry. The kernel's v4l2_h264_init_reflist_builder iterates dpb[] and skips entries with fields == 0 — they count as "no field reference" regardless of VALID/ACTIVE flags. Without this, P-slices that need to walk the reference list (first one in BBB is at frame 11) hit "no valid refs" and S_EXT_CTRLS rejects the request with EINVAL (error_idx == count = kernel's "application bug" sentinel). 2. Skip entries with valid=true but used=false. dpb_update() clears `used` for all entries then re-marks only those in the current ReferenceFrames[] list. Stale entries (frames the consumer has retired from its DPB) were being included, growing the V4L2 dpb[] monotonically until H264_DPB_SIZE while SPS.max_num_ref_frames may be 4. FFmpeg iterates h->short_ref[] / h->long_ref[] only — the currently-referenced set. Empirical: from "10 frames decode, frame-11 P-slice EINVAL" to "~20 frames decode, then a different EINVAL on later frames." Confirms both fixes are correctness improvements but Track A is not yet fully resolved — at least one more bug remains. iter4 stays open. 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.