[Libav-user] Questions with avf_showspectrum.c

Ricky Huang rhuang.work at gmail.com
Thu May 15 03:54:45 CEST 2014

Hello all,

I am currently examining avf_showspectrum.c and I have a few questions that I am hoping you guys can clarify for me:

(This is the command I am running, BTW: ./ffmpeg -i input.mp3 -filter_complex showspectrum=mode=separate:color=intensity:slide=0:scale=cbrt -y output.avi)

1)  First it is about the output: I am assuming the plotted image has time horizontally, the frequency range vertically, and the intensity of color as the amplitude.  Is that correct?

2)  In plot_spectrum_column() function, the code copies some amount of the data to the rdft_data:
>   s->rdft_data[ch][start + n] = p[n] * s->window_func_lut[start + n];

and then performs a av_rdft_calc() on the data.  But it's never clear the s->rdft_data array, does this mean the plot is cumulative over time?

Thanks in advance.
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