[FFmpeg-devel] [RFC] AAC Encoder

[Michael Niedermayer]

On Sun, Aug 24, 2008 at 07:33:56AM +0300, Kostya wrote:
> On Sat, Aug 23, 2008 at 08:39:19PM +0200, Michael Niedermayer wrote:
> > > the code was
> > > for(i = 1; i < info->num_windows; i++)
> > >     put_bits(&s->pb, 1, info->group_len[i]);
> > > 
> > > why can it not be
> > > for(i = 1; i < info->num_windows; i++)
> > >     put_bits(&s->pb, 1, !!info->group_len[i]);
> > > 
> > > ?
> > > 
> > > group_len here can be the actual lens
> > 
> > ping, this is currently blocking quite a few hunks in your patch.
> > I wont forget about it, nor will i skip going over all previous reviews
> > at the end to ensure nothing has been forgotten.
> 
> There could be 1-8 window groups (now it's 3 or 4 but I'll implement a
> better grouping eventually), and the standards says encoder
> should always write 7 bits indicating whether window n+1 starts a new
> window group or not (since window 0 is always a start window), so each
> window group length is represented by a variable number of bits,
> hence the loop in the form you see in my code.
> 
> And I did representing group lengths as in bitstream (if(!group_len[]) continue),
> you didn't like it either.

let me try again, my code apparently didnt reflect what i wanted to suggest

for(i = 1; i < 8; i++)
    put_bits(&s->pb, 1, info->group_len[i] > 1);


Anyway, let me elaborate on what i am trying to achive with this.

currently you use 2 variables all over the place like
        w = 0;
        for(wg = 0; wg < num_window_groups; wg++){
            for(i = 0; i < max_sfb; i++)
                put_bits(pb, 1, ms_mask[w + i]);
            w +=group_len[wg]*16;
        }

with what i suggest, i think this would just be:
        for(w = 0; w < C; w += group_len[w])
            for(i = 0; i < max_sfb; i++)
                put_bits(pb, 1, ms_mask[w][i]);



[...]
-- 
Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

Asymptotically faster algorithms should always be preferred if you have
asymptotical amounts of data
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