[FFmpeg-user] Questions about readout important metadata from DPX files ("logarthmic/linear") and recreate DPX with same metadata

[Carl Eugen Hoyos]

Dave Rice <dave <at> dericed.com> writes:

> >> As far as I tested I can say (for the 
> >> ffv1-supported pixelformats "gbrp10le" and 
> >> "gbrp12le") it works lossless. All FrameMD5s 
> >> are equal:
> > 
> > (This is not the first time that I am slightly 
> > surprised people use FFmpeg to prove that an 
> > encoder of FFmpeg is lossless.)
> 
> Why is this slightly surprising?

Assuming this is done to rule out bugs 
in FFmpeg:
I find it unlikely that ffv1 is not lossless 
and that you will find out like this (as 
opposed to feed random data to the codec).
I find it much more likely that a bug in 
the dpx decoder exists: Since you use the 
same decoder twice in above test you
would not find such a bug.
A bug in both gm and FFmpeg that leads to 
identical output seems less likely to me.

Of course I do believe that framemd5 is 
useful to compare frames.

Carl Eugen