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

[Carl Eugen Hoyos]

2017-05-25 22:39 GMT+02:00 Paul B Mahol <onemda at gmail.com>:
> 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.

Is it related to one of the algorithms listed here?
https://en.wikipedia.org/wiki/Matrix_decoder
It may make sense to mention the used algorithm in the
documentation (or the source code).

>> Does a filter have advantages over an implementation in
>> libswresample?
>
> libswresample doesnt do this.

Yes.
My question was if your implementation shouldn't be
part of libswresample, or rather what would be the
disadvantage.

>> 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.

But it works better for Pro Logic files?

Thanks, Carl Eugen