[FFmpeg-user] Build LGPL version of FFmpeg for Windows

Nicolas George nicolas.george at normalesup.org
Mon Nov 5 18:32:06 CET 2012

Le quintidi 15 brumaire, an CCXXI, Carl Eugen Hoyos a écrit :
> I am really no expert for git but I know for sure that 
> it is not defined through "repositories" but through 
> version hashes (that fate shows prominently).

I confirm. The full SHA-1 hash of a git commit object fully describes (up to
a SHA-1 collision, of course) the exact contents of the source tree after
that the commit, plus the exact contents of all the files' history.

If you have several Git repositories hosting a commit with the same SHA-1,
then pulling it from any of them is rigorously equivalent except for
practical details (bandwidth, availability, etc.; still excepting a hash
collision of course).

The short hash printed sometimes is a part of the full SHA-1. Since it is
much smaller (28 bits, usually, versus 160 bits for the full SHA-1),
collisions happen. The short hash produced by the git tools is long enough
to avoid collisions within a given repository (in other words: if the
repository contains two commits with SHA-1 starting with the same 28 bits,
the git tools will print an eighth nibble for the short hash). That means
that in a convoluted scenario it would be possible for the short hash
printed from a repository to match a different commit in another repository.
In practice, this is very unlikely, and would not go unnoticed. Looking at
the full hash gives certainty.


  Nicolas George
-------------- next part --------------
A non-text attachment was scrubbed...
Name: not available
Type: application/pgp-signature
Size: 198 bytes
Desc: Digital signature
URL: <http://ffmpeg.org/pipermail/ffmpeg-user/attachments/20121105/525bd08b/attachment.asc>

More information about the ffmpeg-user mailing list