On Jun 4, 2014, at 6:09 PM, Ricky Huang <[email protected]> wrote:
> Hello all, > > According to a LAS blog post here: > http://blog.pkh.me/p/6-las-lossy-audio-spotter.html. It says that "the > buffer is composed of couples of real and imaginary floats except for the two > first ones which are the real parts of the first and last bins…" under the > "Processing the audio data" section. > > Does anyone know where that is documented? I looked on ffmpeg's doc > (http://www.ffmpeg.org/doxygen/2.2/group__lavc__fft.html#ga745b8757713a5a0f0347eddcc6ccc9a4) > and sees nothing on that. I also looked at the avf_showspectrum.c code and > it doesn't seem to make the special case for those two positions. Clément, the author of the LAS article, answered the question for me. It is located in a comment in libavcodec/rdft.c: /* i=0 is a special case because of packing, the DC term is real, so we are going to throw the N/2 term (also real) in with it. */ and can be found here: http://www.ffmpeg.org/doxygen/2.2/rdft_8c_source.html#l00071 Just in case anyone run into the same question in the future. > > > Thanks in advance.
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