[FFmpeg-user] Support for Prores4444 12bit files

[Robert Krüger]

Hi,

Apple's whitepaper states that Prores4444 has "up to 12bit" color
depth. There are no Apple tools that I know of that have a switch to
produce such a 12bit beast (their professional transcoder "Compressor"
has the options "16.7 million colors" or "more than 16.7 million
colors" which is useless in that case as IMO that translates to 8bit
and more than 8 bit).

Now there exist recorders which explicitly claim to support 10bit
_and_ 12bit Prores4444 (see
http://www.sounddevices.com/products/pix240i/sample-files/) and I
downloaded those and tested transcoding with ffmpeg and the output
looks fine. Since the pixel formats used by ffmpeg for Prores are 10
bit only, I am wondering if there is a way to test if the color depth
is really 12bit and thus reduced in any transcoding.

Could anyone with more intimate knowledge of the decoder(s) shed some
light on this? Is the current decoder reducing bit depth of these
files when decoding and if so are there plans to add support for a
pixel format that allows for 12 bit?

Is there a way of testing such a file if it is 10 or 12bit? Apart from
the alpha channel (which in this case is not there) neither the header
documentation at
http://wiki.multimedia.cx/index.php?title=Apple_ProRes nor the source
code reveal anything that would be suitable for making that
distinction? Or is the formulation "up to 12bit" simply wrong and
Prores4444 is always 12bit?

Best regards,

Robert

P.S.: I am not talking about 10 bit files with a special gamma
function like Arri Log-C or Sony S-Log but real 12bits of depth.