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

Christoph Gerstbauer christophgerstbauer at gmail.com
Thu Mar 12 17:09:35 CET 2015

>> But let me try it differently:
>> You have an input file with a logarithmic
>> colour space that is not supported by FFmpeg.
>> If you are sure that you know what you are
>> doing, you can of course use FFmpeg to
>> compress your raw data (I believe ffv1 was
>> tested much better already but this is not
>> really related). But while the data will
>> still be identical the colourspace will
>> be linear because FFmpeg only supports
>> linear colourspaces. So you will will have
>> to "know" that the actual content is
>> logarithmic when you use it again (or
>> write the transfer information when
>> creating the file).
> yes that is what I am planing to do.


I tested a LOG C ARRI ProRes444 file (logarithmic values) to convert it 
to a linear ffvhuff.
For that I used a specific LUT file from ARRI and the 3dlut videofiler.
That works good.

ffmpegnew -i "I:\ARRI SAMPLE FILES\J001C048_140110_R6MS.avi" -vf 
lut3d=file=AlexaV3_K1S1_LogC2Video_Rec709_EE_davinci3d.cube" -vcodec 
ffvhuff -pix_fmt yuv444p10le -acodec copy "I:\ARRI SAMPLE 

So, if I can readout the information that the input video file or input 
DPX file has logarithmic values I can
a) keep the logarithmic encoding in the ffv1 archive file and save the 
metadata information in an external file/database or
b) I decide to linearize it with LUT and 3dlut filter to have a 
linearized master in the archive beneath the original DPX file of course.

But, the readout of the metadata has to be made with mediainfo at this 
time. It would be very useful if FFmpeg would get a more detailed 
metadata readout function for DPX files.
At least for readout of the "logaritmic/linear" information and the 
FrameRate information -> FFmpeg always "thinks" that the fps of my DPX 
files ar 25fps.

There exist one DPX metadata reader/editor only for MAC OS.
Which this tool I checked the FrameRate values in the DPX: most DPX had 
no value written, so ffmpeg GUESSES the fps I think.
One DPX had the value 24fps, but FFmpeg also showed me "25fps".
Anyhow: I am not shure if this metadata reader is THE reference 
application for DPX. :/ I just mentioned it that there are more 
informations in the DPX than ffprobe is able to show me.


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