[FFmpeg-user] Support for Prores4444 12bit files

[Robert Krüger]

On Thu, Jul 4, 2013 at 5:25 PM, Paul B Mahol <onemda at gmail.com> wrote:
> On 7/4/13, Robert Krueger <krueger at lesspain.de> wrote:
>> 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.
>
> I think you are confused. There is no 12bit prores.

OK, so your theory is:
- Apple's official whitepaper is bullshit
- http://www.sounddevices.com/products/pix240i/specs/ + a lot of
articles about it are fraud or just bullshit

Definitely possible though it does not sound too likely and i am
trying to find out. But you are correct. I am indeed confused.

>
> Why would 12 bit prores file be smaller than 10 bit one?

File size for a video file with a de-factor VBR codec would always
depend on a lot of factors
1) the exact motive
2) noise of the camera under the conditions used to record each clip
3) exposure time of the camera
4) the way bitrate control is implemented/tuned for the given codec/setting

If those were exactly the same for both clips, then I would say, you
are right and it cannot be.