claude-noether
c106d95869
Refactor request.c::find_video_node_via_topology to find_decoder_video_node_via_topology — walks media-topology entities looking for MEDIA_ENT_F_PROC_VIDEO_DECODER function, then follows the kernel's link graph (data link from proc to IO entity, interface link from IO entity to V4L_VIDEO interface) to the correct /dev/videoN. Two-pass find_codec_device: pass 1 accepts only "rkvdec" (multi-codec decoder, 3 of 5 codecs); pass 2 accepts any known_decoder_drivers entry. Pre-iter7 the walk picked whichever media device matched the hantro-vpu driver name first — which on RK3399 could be the encoder half of the same media device, surfacing as an empty profile list. Phase 5 amendments incorporated: - CRIT-1: use MEDIA_LNK_FL_INTERFACE_LINK (1U<<28) to discriminate interface vs data links. - CRIT-2: check both source_id and sink_id of each link. - IMP-3: 2-call MEDIA_IOC_G_TOPOLOGY pattern (allocate all 3 arrays before second call); pre-iter7 had a spurious memset + third call. iter4-B1b (multi-decoder routing — open BOTH rkvdec AND hantro from one backend instance) still deferred. Post-iter7 MPEG-2/VP8 (hantro) still need LIBVA_V4L2_REQUEST_VIDEO_PATH override. Signed-off-by: claude-noether <claude-noether@reauktion.de>
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.