Allow use of avconv on systems where it has replaced ffmpeg

[GoogleCodeExporter]

libav and avconv have replaced ffmpeg on Ubuntu and similar Linux 
distributions.  It would be great if video4fuzez could use Exceptions to 
failover to avconv if ffmpeg is not available.

Original issue reported on code.google.com by willfurn...@gmail.com on 12 Jul 2014 at 10:27

[GoogleCodeExporter]

Wow, I didn't expect for video4fuze to be still used by anyone :D

Unfortunately my fuze broke some years ago and I would have no way of testing 
videos produced by avconv. I also have no idea of which parameters should be 
used to match the ffmpeg parameters.

If there was a wrppaer around avconv and libav which used the same command-line 
interface as ffmpeg, that would work for video4fuze, but I don't know wether 
that exists.

Original comment by ssorga...@gmail.com on 13 Jul 2014 at 7:08

[GoogleCodeExporter]

Yes, it's still used.  Thanks for the work on this - I'm still very much 
reliant on my ageing Fuze and also like the project for nicely demonstrating 
how to write a simple PyQt/PySide-powered UI.  

Looks like a crude find and replace of ffmpeg with avconv works on my Linux 
Mint 17 box for a 30s MP4 downloaded using youtube-dl, although only the first 
100 of the temporary jpg files created by avconv are deleted.

Original comment by willfurn...@gmail.com on 14 Jul 2014 at 8:26