[FFmpeg-devel] [PATCH] avcodec: add Actimagine VX video decoder

[Lynne]

Mar 15, 2021, 21:20 by fnouwt2 at gmail.com:

> Good to know the order doesn't matter. In that case I should be able to use
> it!
>
> I don't have any docs about the format because it's all proprietary, but I
> did some testing with the official codec for windows and the color
> conversion I reverse engineered from the decoder used in ds games
> r = y + (v << 1)
> g = y - (u >> 1) - v
> b = y + (u << 1)
> results in colors that are equal to whatever I throw into the codec and
> frames that are 1:1 equal to the output of the decoder included in the
> windows codec.
>

That's looking really close to YCoCg. In fact it probably is just a variant of
YCoCg. You should be able to convert between both with no loss of quality
or rounding errors and just mark the output frame as being YUV with a
YCoCg colorspace. The wikipedia page on YCoCg has RGB<->YCoCg
conversions you can follow.


> I suppose that I would just have to allocate an extra frame if I wanted to
> do conversion to normal yuv colors. That frame would then be returned and
> the original frame would be put in the ref queue.
>

You could implement an inverse step when you use the reference frames,
but for such a codec, where the frame size is going to be comparitively
tiny, I think you can just get away quicker with copying and the converting
the copied frame, while keeping your ref frames as-is.