[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 11:37:31 EEST 2016

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

> A .mov source with no SAR/DAR information (listed as #sar 0: 0/1) 
> in the framemd5, has specific SAR information when remuxed as mkv 
> (#sar 0: 1/1). Obviously these values are also available via 
> ffmpeg -i input.

Not really:
The muxer does not write a value if sar == 0/1 (the field is not 
mandatory) but the demuxer always provides a value to the world.
You could read the mkv specification in a way that this is 
correct (because a sar of 1/1 is the default for mkv).

Does the demuxing behaviour hit you?
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.

Carl Eugen

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