Once you’ve downloaded the video, it should play on most computers using Quicktime or VLC. If you find you can’t play the video, one possible explanation is that it didn’t get converted from the .flv format to .mp4 after download. This is probably because you haven’t installed ffmpeg.
Actually, the latest version of VLC (0.9.9) seems to be able to play the .flv file without conversion.
For some devices, you will need to convert the downloaded video. Also, if you want to write it to a DVD, you will probably need to convert it.
next: Converting iPlayer video