[FFmpeg-devel] [PATCH] lavfi: phasescope filter

[Paul B Mahol]

On 3/30/13, Stefano Sabatini <stefasab at gmail.com> wrote:
> On date Thursday 2013-03-28 23:46:38 +0100, Stefano Sabatini encoded:
>> On date Monday 2013-03-25 22:23:51 +0000, Paul B Mahol encoded:
>> > +    for (i = 0; i < nb_samples; i++) {
>> > +        int x, y;
>>
>> > +        for (chan = 0; chan < 2; chan++, ptr += 2) {
>> > +            x = ((ptr[1] - (int)ptr[0]) / (float)UINT16_MAX + 1) * hw;
>> > +            y = ((ptr[0] + (int)ptr[1]) / (float)UINT16_MAX + 1) * hh;
>> > +            dst = &p->outpicref->data[0][y * linesize + x];
>>
>> Can you explain the mathematical principle, or provide a link for it?
>
> well, not really needed, there is nothing to explain.
>
> A small gallery:
> ffplay -f lavfi
> "aevalsrc=cos(2*PI*t*200):cos(2*PI*t*201),asplit[out0],phasescope=s=300x300:r=30:dissolve=10,boxblur=2:2,negate[out1]"
> ffplay -f lavfi
> "aevalsrc=cos(2*PI*t*200):sin(2*PI*t/10)*sin(2*PI*t*400+2*PI*sin(2*PI*t/20)),asplit[out0],phasescope=s=300x300:r=30:dissolve=10[out1]"
> ffplay -f lavfi
> "aevalsrc=cos(2*PI*t*200):sin(2*PI*t/10)*sin(2*PI*t*400+2*PI*sin(2*PI*t/20)
> +
> 13*cos(2*PI*t/13)),asplit[out0],phasescope=s=300x300:r=30:dissolve=10[out1]"
>
> What I can't understand:
> ffplay -f lavfi
> "aevalsrc=cos(2*PI*t*200):cos(2*PI*t*200),asplit[out0],phasescope=s=300x300:r=30:dissolve=10[out1]"
>
> In this case we have:
> ptr[1] - ptr[0] = 0
>
> and thus x = 0, so I'd expect a single vertical line. What am I
> missing?

That you are using older buggy version.
And better/next name for filter is going to be avectorscope.

aphasescope is more like function that do stereo input -> [-1, 1] ,
with optional graph that display how it changes through time. (similar
to showspectrum)

>
> [...]
> --
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