test0r
c672f19f44
fourier's h264_va_picture_to_v4l2 never assigns sps->level_idc; the field stays at zero-init. level_idc=0 is invalid per the H.264 spec (lowest legal value is 10, Level 1.0). Hantro and other stateless H.264 decoders use level_idc to pre-allocate decoder resources (DPB size, motion-vector buffers); when fed an invalid level the hantro kernel driver silently skips the decode-hardware dispatch — the V4L2 request completes with no error, DQBUF returns the CAPTURE buffer reporting bytesused=3655712 and no V4L2_BUF_FLAG_ERROR, but the buffer is never written. VAAPI's decode-side VAPictureParameterBufferH264 structurally does NOT include level_idc — `grep level_idc va/va.h` returns only hits inside VAEncSequenceParameterBufferH264 (the encode path). The H.264 SPS NAL is also not included in VASliceDataBuffer because ffmpeg-vaapi parses it client-side and forwards only slice data (verified empirically via patch 0010's hex-dump of the OUTPUT buffer: it contains "00 00 01 65 ..." — i.e. ANNEX_B start code + IDR slice NAL byte, no SPS NAL). A SPS-NAL byte extractor is therefore not viable from the bitstream libva-v4l2-request receives. Workaround: hardcode level_idc = 51 (= Level 5.1, max for 1080p and 4K@30 mainstream consumer profiles). This INTENTIONALLY OVER-ALLOCATES decoder resources but is sufficient for any stream up to 4K@30. It is corpus-correct, not contract-correct: a 4K@60 stream (Level 6.x) would under-allocate. This patch is a known-incomplete intermediate, not a final fix. The proper upstreamable answer is a level-from-resolution derivation per H.264 Annex A.3 (max MB rate / max frame size thresholds). That requires mapping consumer-side framerate which VAAPI does not expose, so the lookup table is non-trivial. The TODO is captured inline. This patch's goal is unblocking decode-hardware engagement on the ohm_gl_fix corpus while the full level-derivation work proceeds. Cross-reference: kernel doc ext-ctrls-codec-stateless.rst V4L2_CID_STATELESS_H264_SPS lists level_idc as a required field with no "kernel-derives" annotation — i.e., userspace-required. 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.