[FFmpeg-devel] [PATCH] NellyMoser audio decoder v2
Thu Sep 27 10:21:36 CEST 2007
Lo?c Minier wrote:
> On Sun, Sep 23, 2007, Benjamin Larsson wrote:
>> Thanks for the hint. I can now see that this is clearly a mdct based codec.
>> unpack_coeffs(buf, aptr); -> pre rotation
>> center(aptr); -> fft permutation
>> inverse_dft(aptr); -> inverse fft
>> complex2signal(aptr); -> post rotation
>> apply_state(s->state, aptr); -> window and reorder
>> ff_nelly_state_table -> should be regular sine window
>> ff_nelly_neg_unpack_table -> pre/post rotation factors
>> ff_nelly_inv_dft_table -> fft twiddle factors
>> ff_nelly_center_table -> fft bit reverse table
>> All in all a standard mdct by fft. Should be replaceable by the ffmpeg
>> mdct routines.
> I already replaced inverse_dft() by the fft functions from dsputils in
> my local repo, but I guess this is now pointless as the almost all the
> code should be replaced by a mdct instead.
Hi, I had some time yesterday and looked closer at the code. While there
is no doubt that the code is a TDAC implementation it doesn't seem like
the code can be replaced by the mdct code in ffmpeg. So I guess that the
fft replacement is what can be clean up for now. I'll sort out the table
generation for the rotations and the window.
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