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

3 Apr 2008

      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

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