[FFmpeg-user] Why does encoding a file on different VM hosts result in different file size?

Moritz Barsnick barsnick at gmx.net
Fri Aug 15 18:46:42 CEST 2014

On Fri, Aug 15, 2014 at 17:37:41 +0200, Werner Robitza wrote:
> Oh indeed! Disregard this then.


> I might have spotted a difference in file size with another set of
> commands though.

Please do come back if you can reproduce it.

You are running
- the identical virtual machine
- with the identical OS and binaries and libs
- on the identical host HW
though, are you?

The only thought I could come up with was that your different VM
"hypervisors" or engines do different abstraction of certain CPU
features and commands. ffmpeg/x264 _might_ take a different code path
then, due to runtime detection. Just a wild guess though.

BTW, the codec being lossless doesn't mean the video size needs to be
the same, varying compression is certainly a feature.


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