Posted 08 January 2013 - 22:05
If it's a MKV, you can actually set an AR in MKV Merge. That said not all players/decoders/splitters support it, but it is worth a shot.
Only some get it from the container, that's why it doesn't always work, some read the AR from the actual video itself ( like the h264 inside a MP4 and most MKV's ), which Cannot be changed without re-encoding.
If it's not a MKV, you can demux, and then remux it into a MKV. That is, if you are fine with MKV's..