[FFmpeg-user] Levels and Primaries

Carl Eugen Hoyos cehoyos at ag.or.at
Wed Feb 12 12:11:07 CET 2014

Rio Kierkels <riokierkels <at> gmail.com> writes:

> Could be just my paranoia, but I always have the feeling
> that the decoder does some magic on the numbers or something.

(This may now be the terminology problem in the other 
Concerning the decoder, I suspect that there actually is a 
guarantee that an MPEG decoder in FFmpeg really only 
outputs MPEG levels (unless told otherwise).
But is that really your question?

> Which is why right now I'm also not certain what 
> I'm looking for in the output.

I thought you are looking for levels from 0 to 15 and 
236 to 255 (but as said, I may just not understand the 
problem that you say don't exist).

> I think it's on a byte level.

Of course?

> So yeah if I've got the time I'll be going through 
> the mxf files byte by byte...

Why not rawvideo which would make the task 
indefinitely easier imo?


> That is why currently I'm content with the
> assumption that ffmpeg does the correct thing 
> until I have the means to completely verify this 
> myself when my coding and color science skills 
> are of such a level that I can be confident
> that I'm doing the right thing.

Do you mean you want to improve your coding skills 
so that you can (mathematically if you want) show 
that the scaler does the correct thing?
I don't think this is realistically possible.
But to just test a large number of samples and 
show that for the given samples, the output level 
is always (as in "100%") correct does not need any 
coding skills, just hexdump and grep (or python).

Carl Eugen

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