test0r
4078368104
Patch 0002 sets V4L2_CID_STATELESS_H264_START_CODE to ANNEX_B on the
device, telling the kernel that OUTPUT-buffer payloads will contain
0x00 0x00 0x01 NAL start codes. picture.c::codec_store_buffer has
the prepend logic guarded by `if (context->h264_start_code)`, but
that boolean is set ONLY inside h264_get_controls() — a function
that exists but is never called.
Result: device expects ANNEX_B, libva-v4l2-request feeds raw NAL
payloads with no start codes, kernel cannot find slice boundaries,
hantro emits a zeroed CAPTURE buffer. mpv reports successful decode
because the V4L2 round-trip succeeds (no EINVAL); the visual output
is a flat dark-green frame (NV12 zero through BT.709).
Identified via:
- Patch 0006 cleared the EINVAL cluster-rejection (128 → 0 on
bbb_1080p30) but visual output remained flat green.
- GStreamer reference (gstv4l2codech264dec.c:1363-1377) confirms
start codes are required when ANNEX_B is selected.
- Source-archaeology of fourier's picture.c:67-74 showed the gate
on context->h264_start_code.
Fix: in context.c::RequestCreateContext, immediately after patch
0002's device-control block, set context_object->h264_start_code =
true to match the ANNEX_B mode we just programmed. Hardcoded for
now (matches 0002's hardcoded set); replaced with a runtime probe
in the planned probe-then-set commit.
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.