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

[Michael Niedermayer]

On Tue, Jun 12, 2012 at 08:25:34PM -0600, Pavel Koshevoy wrote:
> 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.

also see 
av_rdft_init() and av_rdft_calc() in case you havnt seen them yet

[...]
-- 
Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

While the State exists there can be no freedom; when there is freedom there
will be no State. -- Vladimir Lenin
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