[FFmpeg-devel] [PATCH] libavcodec/zmbvenc: Add support for RGB formats

[Carl Eugen Hoyos]

2019-03-11 11:37 GMT+01:00, Tomas Härdin <tjoppen at acc.umu.se>:
> fre 2019-03-08 klockan 21:39 +0000 skrev Matthew Fearnley:
>> > On Fri, 8 Mar 2019 at 18:07, Carl Eugen Hoyos <ceffmpeg at gmail.com>
>> > wrote:
>> > 2019-03-08 15:04 GMT+01:00, Tomas Härdin <tjoppen at acc.umu.se>:
>> > >
>> > > Maybe we could coordinate 1/2/4/24-bit support with the
>> >
>> > I believe FFmpeg cannot support 1/2/4 bit for encoding.
>>
>> As far as I can see, FFmpeg has very limited support for bit depths less
>> than 8.  I think there are basically two formats (plus variants), with
>> fixed "palettes":
>> 1bpp: MONO_BLACK / MONO_WHITE (black/white only)
>> 4bpp: RGB4[_BYTE], BGR4[_BYTE] (RGB 1:2:1, 16 colours - I presume red/blue
>> would be 0,255; green would be 0,85,170,255)
>>
>> If the ZMBV formats were defined, these might be worth encoder adding
>> support for.
>> (Practically speaking though, it would be a slight pain, because the
>> encoder would do the work in 8bpp and pack/unpack as needed.)
>> But with PAL8 being the only format allowing a free palette, all sub-8bpp
>> formats would have to decode to that, so they wouldn't round-trip.
>
> There's some justification for adding sub-8bpp, like BMP. bmp.c
> converts all of them except GRAY8 to PAL8. Bitdepths besides 1, 4 and 8
> don't work at all.
>
> One way to at least allow both the bmp and zmbv encoders to do sub-8bpp
> from PAL8 would be to keep track of the maximum number of colors in
> some appropriate struct.

bits_per_coded_sample

Carl Eugen