test0r
affb4bd12a
Diagnostic-only. Investigating the observed anomaly:
- V4L2 strace shows decode_params.top_field_order_cnt = 65536
on the first IDR frame submitted by mpv+ffmpeg+libva-v4l2-request
- GStreamer's reference path writes 0 (spec-correct: PicOrderCnt=0
for IDR with pic_order_cnt_type=0 / pic_order_cnt_lsb=0)
- Reading FFmpeg source (libavcodec/vaapi_h264.c::fill_vaapi_pic):
va_pic->TopFieldOrderCnt = 0;
if (pic->field_poc[0] != INT_MAX)
va_pic->TopFieldOrderCnt = pic->field_poc[0];
For IDR: ff_h264_init_poc sets field_poc[0] = poc_msb + poc_lsb
= 0 + 0 = 0. So FFmpeg should write 0.
If FFmpeg writes 0 but fourier reads 65536, the mismatch is in the
libva ABI between ffmpeg's writer and our reader. Most likely
suspect: VA_PADDING_LOW size in VAPictureH264 differs between the
libva headers ffmpeg+libva were built against and the headers
fourier was built against, shifting struct field offsets.
This patch dumps:
1. sizeof(VAPictureH264) at our reader's view
2. First 32 raw bytes of VAPicture->CurrPic
3. Field-decoded values via the .picture_id, .frame_idx, .flags,
.TopFieldOrderCnt, .BottomFieldOrderCnt accessors
If the raw bytes show 00 00 01 00 at offset 12 (= 65536 LE), the
field offset is correct and FFmpeg actually wrote 65536 — meaning
either FFmpeg has a bug, or our test scenario triggers a non-spec
code path. If the raw bytes show 00 00 00 00 at offset 12 but
TopFieldOrderCnt accessor returns 65536, the struct ABI is
mismatched and we need to reconcile libva versions.
If sizeof(VAPictureH264) prints as something other than 36 (= 4*5
+ 4*VA_PADDING_LOW assuming VA_PADDING_LOW=4), the struct layout
on this build differs from the documented libva-2.x layout.
Removed once the source of the 65536 is identified.
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.