Ensure the first audio stream is selected as the default stream when no video stream is present.
Ensure the first audio stream is selected as the default stream
when no video stream is present.


git-svn-id: a4d7c1866f8397a4106e0b57fc4fbf792bbdaaaf@13648 9553f0bf-9b14-0410-a0b8-cfaf0461ba5b

prajnashi/ffmpeg,prajnashi/ffmpeg,prajnashi/ffmpeg,prajnashi/ffmpeg