Re: [PATCH v1] media: v4l2-core: Initialize h264 scaling matrix

[AngeloGioacchino Del Regno]

Il 18/02/22 19:42, Nicolas Dufresne ha scritto:
> In the final H264 API, it is not required to set scaling matrix if
> they are not present in the bitstream. A flag was added in order to let
> the driver know. The downside is that it leaves the default control
> value to 0, which isn't valid. As per the spec (see formulas 7-8/7-9),
> when the scaling matrix are absent from the bitstream, flat values
> of 16 should be used. This improves this control semantic in a way
> that the control value are always valid. Drivers can then use
> the scaling_matrix control values without having to check its presence.
> Same method was employed for MPEG2_QUANTISATION.
>
> This fixes issues with MTK VCODEC H264 decoder when using GStreamer.
> GStreamer does not set this control if its not present in the bitstream.
> As MTK VDCODEC was using the initialized to 0 values, the frames ended
> up completely gray.
>
> Fixes: 54889c51b833d236 ("media: uapi: h264: Rename and clarify PPS_FLAG_SCALING_MATRIX_PRESENT")
> Signed-off-by: Nicolas Dufresne <nicolas.dufresne@xxxxxxxxxxxxx>

Tested-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@xxxxxxxxxxxxx>