Software :: Download Helper Screen Capture With Ffmpeg ?

The sort of add on for Firefox 'download helper' now has a new screen capture thing, in case it won't download the video from a particular site. You click the red button and a purple boundary appears round the video frame. I assume this is the basic function of the thing; it then provides the geometry of the purple frame to the program you've given it to capture the video.

By default the program it uses is 'recordmydesktop'. I've tried using this but get sound from the laptop's internal microphone, not the video. Tried 'pavucontrol' to remedy this but it says (wrongly) that no program is recording, so can't put things right.

So tried using ffmpeg: [URL]

Assume the stuff in curly brackets is what download helper supplies. Sometimes works perfectly but with B.BC. i-player only get the top left hand corner of the video and it is stretched somewhat horizontally.