[FFmpeg-devel] [PATCH] avfilter: add audio surround upmixer

Paul B Mahol onemda at gmail.com
Thu May 25 23:39:18 EEST 2017

On 5/25/17, Carl Eugen Hoyos <ceffmpeg at gmail.com> wrote:
> 2017-05-25 16:45 GMT+02:00 Paul B Mahol <onemda at gmail.com>:
>> + at section surround
>> +Apply audio surround upmix filter.
>> +
>> +This filter allows to produce multichannel output from
>> stereo audio stream.
> Does this work on Pro Logic-encoded files (ticket #4085)
> or does this filter use a different algorithm?

It works with sample from that ticket.
It uses own algorithm.

> Does a filter have advantages over an implementation in
> libswresample?

libswresample doesnt do this.

> Iirc, our Pro Logic downmixer has an issue with "phase shift"
> (ticket 3455 / 4175): Does this filter give expected output
> for FFmpeg-encoded files or original Pro Logic files (or is
> there no difference on upmixing)?

FFmpeg downmixing, while certainly not correct, is giving reasonable
output when used with this filter.

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