[FFmpeg-user] Matroska encode specifies SAR/DAR when no aspect ratio info is present in source .mov

Carl Eugen Hoyos cehoyos at ag.or.at
Wed Jul 13 12:25:22 EEST 2016

Kieran O Leary <kieran.o.leary <at> gmail.com> writes:

> > Does the demuxing behaviour hit you?
> It only means that I have to come up with a different way (ignore 
> the commented lines in framemd5 output) of diffing input/output 
> framemd5 files when transcoding, which I should be doing anyway.

I would expect that there are cases when FFmpeg 
changes the timebase when remuxing.

> > It could be changed but this is isn't completely trivial:
> > For 3D files, the SAR is 2/1 (or 1/2) by default, so in this
> > case, the demuxer would still have to output a sar although
> > not specified in the file.
> I understand. I don't know how essential it is, seeing as no 
> SAR would mean 1:1 anyhow.

> The only case that I can think of is if an archivist was 
> really desperate to preserve as many properties of the 
> original file when remuxing to another container.

As said, the SAR property is (at least for non-3D content) 
correctly preserved, including the no-SAR case.
But I would expect that many other properties cannot be 
preserved when remuxing (and this isn't necessarily 

> Seeing as PAR/SAR is a significant property of the source, 
> its declaration, or non-declaration possibly should be 
> preserved, even if players will treat the file the same way 
> regardless.

SAR is important and is correctly preserved in mkv (at 
least for 2D content).

> I can probably live without it as I'd prefer if the SAR 
> was declared in the source to begin with.

MS avi does not know about SAR...

Carl Eugen

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