[FFmpeg-devel] [PATCH] RDFT for Bink audio
Thu Jan 15 17:08:22 CET 2009
On Thu, Jan 15, 2009 at 4:25 AM, Benjamin Larsson <banan at ludd.ltu.se> wrote:
> Alex Converse wrote:
>> Attached is an implementation of the Real Discrete Fourier Transform as
>> required for Bink Audio.
>> Alex Converse
> Hi, Bink audio has 2 modes:
> + if (s->use_dct)
> + ff_dct_calc (&s->trans.dct, coeffs);
> + else
> + ff_rdft_calc(&s->trans.rdft, coeffs);
> Did you implement both modes in this patch ? To me it looks like we also
> need a dct function also.
Separate transform will be in a separate patch.
> + ev.re = k1*(data[i1 ]+data[i2 ]);
> + od.im = k2*(data[i1 ]-data[i2 ]);
> + ev.im = k1*(data[i1+1]-data[i2+1]);
> + od.re = -k2*(data[i1+1]+data[i2+1]);
> + /* Apply twiddle factors to the odd FFT and add to the even FFT */
> + data[i1 ] = ev.re + od.re*tcos[i] - od.im*tsin[i];
> + data[i1+1] = ev.im + od.im*tcos[i] + od.re*tsin[i];
> + data[i2 ] = ev.re - od.re*tcos[i] + od.im*tsin[i];
> + data[i2+1] = -ev.im + od.im*tcos[i] + od.re*tsin[i];
> That part of the code looked like some code we have in the qdm2.c
> decoder ? Can you look and see if it matches? I have always wondered
> what kind of transform it was.
It is clearly a IRDFT with something weird going on with the 0 and N/2
points. Do you know anything about the genesis of that code that isn't
in your pdf? The n2 term is clearly not passed to the FFT at all.
> Code wise other then some strange indentation in the struct it looked ok.
Some tabs crept in, try this.
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