How to reproduce:
1. Open QA attached project
2. Make a backup of the meta file for asset file
3. Switch platform
4. Compare new and old meta files

Expected behaviour: Meta files are identical if the file was transcoded to the same format
Actual behaviour: Meta file have changed, even when transcoded file is identical, which results in litter in Version Control Systems

Reproduced on: 2017.1, 2017.2
Not reproduced on: 2017.3.0b1

Fixed together with Case 946826
https://issuetracker.unity3d.com/issues/videos-are-being-transcoded-when-switching-platform-even-when-they-are-cached-in-cache-server