Switching aspect ratios?

[Coda A27]

If I changed a video from 4:3 to 1:1 (by accident), would converting it back to 4:3 show a loss of information?

[El Torro]

Every time you convert, you loose a little bit of quality... but it shouldn't be too bad

[snorkel]

You didn't say which format you are working with.. Mpeg1 or Mpeg2.. but in general, you should be able to modify the aspect without quality loss, because you're not really re-encoding the video just changing some flags in the video stream.

Mpeg1 has one flag at the beginning of the stream (file), but Mpeg2 can have many throughout the stream. But, keep in mind, even if you change the appropriate flags it might not make any difference because some multimedia players disregard the aspect ratio flag(s) altogether and calculate and display the video as they see fit.

Mpeg1 aspect ratios can be changed with MpegEd:
http://members.tripod.com/wessweb/

Mpeg2 is a bit more tricky, you might have to demux the file first (and remux afterwards). My favorite Mpeg2 stream modifier is ReStream:
http://shh.dvdboard.de/

-s.