[FFmpeg-soc] [soc]:?r2021?-?in?eac3:?ac3dec.h?ac3dec_data.c?ac3dec_data.h?eac3dec .c

[Michael Niedermayer]

On Thu, Apr 03, 2008 at 11:53:22PM +0200, Bartlomiej Wolowiec wrote:
> On niedziela, 30 marca 2008, Michael Niedermayer wrote:
> > Note, to add the header into the buffer calling ff_combine_frame() with
> > END_NOT_FOUND and a smaller buffer size should work.
> >
> > After its in the buffer you just run the header decoder thing over the
> > header and when you know the final frame size you call ff_combine_frame
> > with appropriate next value.
> >
> > Anyway iam not insisting on you changing the current aac/ac3 parser to use
> > ff_combine_frame()
> > But what you will end up implementing will be quite similar in
> > functionality to ff_combine_frame()
> >
> > [...]
> 
> Hmm...
>  I tried to implement it using ff_combine_frame, but the code which I got is 
> in my opinion significantly worse. Main problems which I had:
> -ff_combine_frame is rather adapted to using on one frame, when in buffer is 
> one frame and it currently reads the next one  it isn't convenient (the whole 
> buffer size is not just a new frame's size, so that we should remember size 
> of earlier frames).
> -in the genuine code there is 
> memmove(s->frame_start, s->frame_start + 1, s->header_size - 1);
> s->frame_ptr--;
> here we can operate on pc->buffer and pc->index (remembering also where the 
> new frame begins). However, surely it isn't the simpliest solution... 

What i had in mind is below, this is blindly written and likely contains bugs.
I did spot one each time i looked at it :)
But it does not look fundamentally worse to me, it also has the advantage that
its not full of unneeded memcpys and memmoves.

while(s->remaining_size <= buf_size){
    if(s->remaining_size && !s->need_next_header){
        i= s->remaining_size;
        s->remaining_size= 0;
        goto output_frame;
    }else{ //we need a header first
        for(i=s->remaining_size; i<buf_size; i++){
            ctx->state= (ctx->state<<8) + buf[i];
            if((len=parse_header(ctx->state, &s->need_next_header, &s->new_frame_start)))
                break;
        }
        i-= header_size;
        if(len>0){
            s->remaining_size= len + i;

            if(pc->index+i > 0 && s->new_frame_start){
                s->remaining_size -= i; // remaining_size=len
output_frame:
                ff_combine_frame(pc, i, &buf, &buf_size);
                *poutbuf = buf;
                *poutbuf_size = buf_size;
                return i;
            }
        }else{
            break;
        }
    }
}

ff_combine_frame(pc, END_NOT_FOUND, &buf, &buf_size);
s->remaining_size -= FFMIN(s->remaining_size, buf_size);
*poutbuf = NULL;
*poutbuf_size = 0;
return buf_size;


> Because of that I don't know what to do:
> -leave the code as it is,
> -use ff_combine_frame,
> -write new functions which will operate on the buffer (similar to 
> ff_combine_frame, but adapted to the needs of aac_ac3_parser)?

Do what is simplest and fastest.

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

Freedom in capitalist society always remains about the same as it was in
ancient Greek republics: Freedom for slave owners. -- Vladimir Lenin
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