[FFmpeg-devel] [PATCH] libavfilter: add atempo filter (revised patch v5)

[Pavel Koshevoy]

On 6/12/2012 7:19 PM, Pavel Koshevoy wrote:
> On 06/12/2012 05:07 PM, Michael Niedermayer wrote:
>> On Mon, Jun 11, 2012 at 09:18:02PM -0600, Pavel Koshevoy wrote:
>
> [...]
>
>>> +/**
>>> + * Prepare filter for processing audio data of given format,
>>> + * sample rate and number of channels.
>>> + */
>>> +static int yae_reset(ATempoContext *atempo,
>>> +                     enum AVSampleFormat format,
>>> +                     int sample_rate,
>>> +                     int channels)
>>> +{
>>> +    const int sample_size = av_get_bytes_per_sample(format);
>>> +    uint32_t nlevels  = 0;
>>> +    uint32_t pot;
>>> +    int i;
>>> +
>>> +    atempo->format   = format;
>>> +    atempo->channels = channels;
>>> +    atempo->stride   = sample_size * channels;
>>> +
>>> +    // pick a segment window size:
>>> +    atempo->window = sample_rate / 24;
>>> +
>>> +    // adjust window size to be a power-of-two integer:
>>> +    nlevels = av_log2(atempo->window);
>>> +    pot = 1<<  nlevels;
>>> +    av_assert0(pot<= atempo->window);
>>> +
>>> +    if (pot<  atempo->window) {
>>> +        atempo->window = pot * 2;
>>> +        nlevels++;
>>> +    }
>>> +
>>> +    // initialize audio fragment buffers:
>>> +    REALLOC_OR_FAIL(atempo->frag[0].data,
>>> +                    atempo->window * atempo->stride);
>>> +
>>> +    REALLOC_OR_FAIL(atempo->frag[1].data,
>>> +                    atempo->window * atempo->stride);
>>> +
>>> +    REALLOC_OR_FAIL(atempo->frag[0].xdat,
>>> +                    atempo->window * 2 * sizeof(FFTComplex));
>>> +
>>> +    REALLOC_OR_FAIL(atempo->frag[1].xdat,
>>> +                    atempo->window * 2 * sizeof(FFTComplex));
>>> +
>>> +    // initialize FFT contexts:
>>> +    av_fft_end(atempo->fft_forward);
>>> +    av_fft_end(atempo->fft_inverse);
>> maybe this should call uninit()
>>
>> also if something in this fails then the resuslting state is a mess
>> some arrays one size some others another some memleaks and the ffts
>> might even end with a double free i think
>
> I'll look into that, thank you.
>
>>
>>
>>> +
>>> +    atempo->fft_forward = av_fft_init(nlevels + 1, 0);
>>> +    if (!atempo->fft_forward) {
>>> +        return AVERROR(ENOMEM);
>>> +    }
>>> +
>>> +    atempo->fft_inverse = av_fft_init(nlevels + 1, 1);
>>> +    if (!atempo->fft_inverse) {
>>> +        return AVERROR(ENOMEM);
>>> +    }
>> by using a RDFT you can cut the computations needed down by a factor
>> of 2
>
> My DSP experience is limited.  What is the procedure for computing 
> cross correlation of two signals using rDFT?


I've found this -- http://www.fftw.org/doc/The-1d-Real_002ddata-DFT.html
I'll see what I can do.

     Pavel.