Make .ogg files playable in browsers

Use libvorbis instead of ffmpegs default flac as audio codec to make it real ogg vorbis files instead of flac files in a .ogg container.

'by default flac is used for output in ogg container. add "-acodec libvorbis" as an output option.'
Merge pull request #1 from hubx/master

Make .ogg files playable in browsers