test0r
4246d5d537
Identified by cross-reference against GStreamer's
gst-plugins-bad/sys/v4l2codecs/gstv4l2codech264dec.c (upstream commit
9e3e775). At lines 1263-1304, GStreamer gates SLICE_PARAMS and
PRED_WEIGHTS submission on is_slice_based(self):
if (is_slice_based (self)) {
control[num_controls].id = V4L2_CID_STATELESS_H264_SLICE_PARAMS;
...
control[num_controls].id = V4L2_CID_STATELESS_H264_PRED_WEIGHTS;
...
}
In V4L2_STATELESS_H264_DECODE_MODE_FRAME_BASED, the kernel parses the
bitstream itself from the OUTPUT-queue payload; per-slice controls in
the request trigger cluster-validation EINVAL at error_idx=count
(observed on RK3568 hantro-vpu, kernel 6.19.10).
This patch:
- Reorders controls[] so FRAME_BASED-required entries come first
(SPS, PPS, SCALING_MATRIX, DECODE_PARAMS at indices 0..3) and the
SLICE_BASED-only entries come last (SLICE_PARAMS, PRED_WEIGHTS at
indices 4..5).
- Defaults num_controls=4 (FRAME_BASED), expanding to 5 for
SLICE_BASED and 6 when V4L2_H264_CTRL_PRED_WEIGHTS_REQUIRED.
- Hardcodes slice_based=false for now since patch 0002 sets the
device to FRAME_BASED unconditionally. A TODO marks the spot for
the planned probe-then-set commit, which will populate
context->decode_mode at CreateContext via VIDIOC_QUERYCTRL/
G_EXT_CTRLS and replace the hardcoded false with a runtime check.
Diagnosis chain:
- patch 0005 reduced one EINVAL per frame on PRED_WEIGHTS
submission, but cluster-level rejection persisted at error_idx=5
(count) — meaning kernel walked all 5 controls cleanly but
rejected the request as a whole.
- dmesg silent → rejection in V4L2 core (v4l2-ctrls-request.c /
v4l2-h264.c), not in hantro driver where it could log.
- GStreamer reference confirmed FRAME_BASED contract: only 4
sequence-and-frame-level controls go in the per-request batch.
After this patch the kernel should accept the per-request controls
and actually decode the bitstream into the CAPTURE buffer.
Signed-off-by: Markus Fritsche <fritsche.markus@gmail.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.