[Ffmpeg-devel] [PATCH] faad decoding error return

[Måns Rullgård]

Mike Melanson <mike at multimedia.cx> writes:

> Oded Shimon wrote:
>> Just thought I'd give a status report (and brag) - I can (almost)
>> successfully decode a AAC LC file created with faac! Decoder is very
>> much a mess right now, and I'm not gonna bother posting it here
>> cause it will only work with a very strict set of files (and even
>> those not very well), but I can proudly say I've given my decoder a
>> bitstream and got back human listenable audio... To further brag, it
>> is almost 2 times faster than faad2, even though I made no attempt
>> at optimization. But this might change when the deocder is actually
>> complete...
>
> 	I'm not too surprised about the speed bump if you are using
> 	FFmpeg's get_vlc2() facilities. 5 of AAC's 12 VLC tables are
> 	implemented in FAAD2 as tree-based decoders (the scalefactor
> 	tree may need to traverse up to 19 levels). The weirdest part
> 	is that this approach is apparently recommended by the spec (I
> 	gather this from reading the FAAD2 comments about some
> 	academic paper on optimal AAC VLC decoding).
>
>   *  Optimal huffman decoding for AAC taken from:
>   *  "SELECTING AN OPTIMAL HUFFMAN DECODER FOR AAC" by ......

Optimal in academic context rarely means optimal in any sense that is
of interest in a real-world implementation, least of all speed.

-- 
M?ns Rullg?rd
mru at inprovide.com