[FFmpeg-devel] [PATCH 2/2] lavc/vaapi_hevc: Don't require exact profiles

[Mark Thompson]

On 24/04/2024 14:45, Xiang, Haihao wrote:
> On Ma, 2024-04-22 at 22:23 +0100, Mark Thompson wrote:
>> Rather than turning the constraint flags into a single profile and then
>> searching for that profile (and failing if it doesn't match any profile
>> exactly), instead search all supported profiles and use the first one
>> which supports the given set of constraint flags.
>> ---
>> This fixes decode of rext 8-bit 4:2:0; it will correctly pick Main 12 or Main
>> 4:2:2 10 or Main 4:4:4 (first one available) to use as the decoding profile
>> after this patch.
> 
> sw decoding and vaapi decoding might have different bits (There is the same
> issue if applying Fei's patchset).  
> 
> For example:
> $ ffmpeg -hwaccel vaapi -f lavfi -i testsrc -vf 'format=nv12,hwupload' -c:v
> hevc_vaapi -profile:v rext -vframes 30 -y out.mp4
> 
> 8bit ouput if using sw decoding:
> $ ffmpeg -i out.mp4 -f null - 
> [...]
> Stream #0:0(und): Video: wrapped_avframe, yuv420p(tv, progressive), 320x240 [SAR
> 1:1 DAR 4:3], q=2-31, 200 kb/s, 25 fps, 25 tbn (default)
> 
> 12bit output if using vaapi decoding:
> $ ffmpeg -hwaccel vaapi -i out.mp4 -f null -
> [...]
>  Stream #0:0(und): Video: wrapped_avframe, p012le(tv, progressive), 320x240 [SAR
> 1:1 DAR 4:3], q=2-31, 200 kb/s, 25 fps, 25 tbn (default)

That comes from what the driver reports support for, though?

E.g. with the Intel iHD driver, I have

        {
            "profile": 23,
            "name": "HEVCMain12",
...
                    "surface_formats": [
                        {
                            "rt_format": "YUV420",
                            "max_width": 16384,
                            "max_height": 16384,
                            "memory_types": [
                                "VA",
                                "DRM_PRIME_2",
                            ],
                            "pixel_formats": [
                                "P012",
                                "P016",
                            ],
                        },

So to decode a 4:2:0 8-bit input it is asking for a P012 or P016 surface.

If the driver reported that a Main 12 profile 4:2:0 8-bit input could be decoded to an NV12 surface then it would be picked by the logic in vaapi_decode_find_best_format(), since it would be a better match than the higher-depth formats.

Thanks,

- Mark