Saturday, October 18, 2008

Exponent Strategy

I've been playing around with exponent strategies in Alsophila and came up with what I think is a decent way of selecting them. It is also the first Alsophila feature I have ported back to Aften. The expstr_fast (-fba) option is now expstr_search (-exps) and ranges from 1 to 32.

The previous way of doing this was to select from 5 preset exponent strategy sets for each channel in a frame. The pre-defined sets were originally chosen pretty much by guessing. The new way selects from the 32 sets in the E-AC-3 specification (table E2.14). I sorted them in order of the most commonly used sets by testing various source material and analyzing which sets were used. The new search size option determines how far down this sorted list the encoder searches in order to find the best match.

Friday, October 10, 2008

Wow, it has been quiet a while since my last post. Aften has been somewhat on the back burner in favor of other projects this year. But I have at least been working on AC-3 and E-AC-3, so much of the work I'm doing will help improve Aften in the future.

I have started to do some more work with Alsophila, which is sort of my Aften sandbox project. Channel coupling has been working for a while now, but it's very simplistic. I'm revamping the structure of the encoder to allow a much better CBR mode with adaptive coupling and bandwith. Once I'm happy with that, I'll probably start work on E-AC-3 encoding.

I really didn't like splitting out a new project, but the code structure of Aften was starting to get overwhelming and was making experimentation with new features somewhat difficult. When I get CBR+coupling working well, I'll try to port the changes back to Aften.