[FFmpeg-devel] [PATCH] Implement DCT-I

[Vitor Sessak]

Michael Niedermayer wrote:
> On Tue, Mar 23, 2010 at 04:52:57PM +0100, Vitor Sessak wrote:
>> Michael Niedermayer wrote:
>>> On Sun, Mar 21, 2010 at 12:41:45PM +0100, Vitor Sessak wrote:
>>>> $subj, it is very likely to be useful to the Hilbert transform in the 
>>>> wmavoice postfilter (a  Hilbert filter can be written as a DCT-I + 
>>>> DST-I). The API changes should be backward compatible.
>>>>
>>>> -Vitor
>>>>  avfft.c |    2 +-
>>>>  avfft.h |    8 +++++++-
>>>>  dct.c   |   41 +++++++++++++++++++++++++++++++++++------
>>>>  fft.h   |    2 +-
>>>>  4 files changed, 44 insertions(+), 9 deletions(-)
>>>> ed47ac0f9eefa87df5a03641af1f9f1de1395ec4  dct_I.diff
>>>> Index: libavcodec/avfft.c
>>>> ===================================================================
>>>> --- libavcodec/avfft.c	(revision 22567)
>>>> +++ libavcodec/avfft.c	(working copy)
>>>> @@ -116,7 +116,7 @@
>>>>   #if CONFIG_DCT
>>>>  -DCTContext *av_dct_init(int nbits, int inverse)
>>>> +DCTContext *av_dct_init(int nbits, enum DCTTransformType inverse)
>>>>  {
>>>>      DCTContext *s = av_malloc(sizeof(*s));
>>>>  Index: libavcodec/avfft.h
>>>> ===================================================================
>>>> --- libavcodec/avfft.h	(revision 22567)
>>>> +++ libavcodec/avfft.h	(working copy)
>>>> @@ -77,12 +77,18 @@
>>>>   typedef struct DCTContext DCTContext;
>>>>  +enum DCTTransformType {
>>>> +    DCT_II = 0,
>>>> +    DCT_III,
>>>> +    DCT_I,
>>>> +};
>>>> +
>>>>  /**
>>>>   * Set up (Inverse)DCT.
>>>>   * @param nbits           log2 of the length of the input array
>>>>   * @param inverse         >0 forward transform, <0 inverse transform
>>>>   */
>>>> -DCTContext *av_dct_init(int nbits, int inverse);
>>>> +DCTContext *av_dct_init(int nbits, enum DCTTransformType type);
>>>>  void av_dct_calc(DCTContext *s, FFTSample *data);
>>>>  void av_dct_end (DCTContext *s);
>>>>  Index: libavcodec/fft.h
>>>> ===================================================================
>>>> --- libavcodec/fft.h	(revision 22619)
>>>> +++ libavcodec/fft.h	(working copy)
>>>> @@ -228,7 +228,7 @@
>>>>   * @param nbits           log2 of the length of the input array
>>>>   * @param inverse         >0 forward transform, <0 inverse transform
>>>>   */
>>>> -int  ff_dct_init(DCTContext *s, int nbits, int inverse);
>>>> +int  ff_dct_init(DCTContext *s, int nbits, enum DCTTransformType type);
>>>>  void ff_dct_calc(DCTContext *s, FFTSample *data);
>>>>  void ff_dct_end (DCTContext *s);
>>>>  Index: libavcodec/dct.c
>>>> ===================================================================
>>>> --- libavcodec/dct.c	(revision 22619)
>>>> +++ libavcodec/dct.c	(working copy)
>>>> @@ -37,6 +37,35 @@
>>>>  /* cos((M_PI * x / (2*n)) */
>>>>  #define COS(s,n,x) (s->costab[x])
>>>>  +static void ff_dct_calc_I_c(DCTContext *ctx, FFTSample *data)
>>>> +{
>>>> +    int n = 1 << ctx->nbits;
>>>> +    int i;
>>>> +    float next = -0.5f * (data[0] + data[n]);
>>> data[n]
>>> is that not out of the array?
>> No, it is just that I forgot to mention in the doxy that DCT-I needs an 
>> array 1 element longer.
>>
>>>> +    float tmp;
>>>> +
>>>> +    for(i = 0; i < n/2; i++) {
>>>> +        float tmp1 = data[i    ];
>>>> +        float tmp2 = data[n - i];
>>>> +        float s = SIN(ctx, n, 2*i);
>>>> +
>>>> +        next += tmp1 * COS(ctx, n, 2*i);
>>>> +        next -= tmp2 * COS(ctx, n, 2*(n-i));
>>> is COS(ctx, n, 2*i) == -COS(ctx, n, 2*(n-i))
>>> ?
>> yes
>>
>>> if yes, where is this algorithm from?
>> Numerical recipes (the text, not the unreadable fortran-born mess).
> 
> good, then it should be optimal
> 
> 
>> New patch with decent documentation and a discrete sine transform 
>> implementation.
>>
>> -Vitor
> 
>>  avfft.c |    2 -
>>  avfft.h |   18 +++++++++++----
>>  dct.c   |   75 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++------
>>  fft.h   |   11 +++++----
>>  4 files changed, 90 insertions(+), 16 deletions(-)
>> 9b3d54b931800a2c439479490d7efd648847cd1d  dct_dst.diff
> 
> patch should be ok if tested

Tested and applied.

-Vitor