What does the frame drop-down box mean next to ac3?

[Triggerle]

In the bitrate tab, if you select an ac3 file, there is a drop-down box with the tilte "Frame". What does that do?

[TheWEF]

that's the interleave interval.
you have to use the same interval for ac3 interleaving in the audio tab of the encoder-window later on.
bigger interval -> less overhead but probably jerky playback (depends on your system).
i recommend to use 1 frame, but for some people 2 works better. some even need to mux manually in nandub with a crooked millisecond interval (not supported in gknot) to get smooth playback.

wef.