[vlc-devel] 5.1 to stereo plugin with lookahead

[Mikel Astiz]

Hello,

 

We are trying to develop a plugin for VLC, which mixes the 6 channels of
a 5.1 source into a stereo output, just like
"modules/audio_filter/channel_mixer/headphone.c" does.

 

However, there is an important issue: our algorithm needs to have not
only the current sound signal (and the past), but also some seconds in
the future. In other words, to be able to calculate the output of a
certain time T, we need to have the data ranging from [T-K1 to T+K2],
where K1 and K2 involve several seconds (about 5, for example).

 

(This behaviour is inherent in the algorithm and impossible to modify,
so please do not focus on this issue)

 

We've been trying different approaches, using audio filters or audio
mixers, but the function DoWork apparently is never given the sound
signal of the "future". Could someone confirm this? COULD SOMEONE
CONFIRM THAT YOU CANNOT OBTAIN THE SAMPLES BEYOND THE CURRENT POSITION
OF THE VIDEO?

 

The only solution we have found so far is to use the parameter "Audio
desynchronization compensation". This can delay the video output, and
makes it possible to have all the audio input several seconds before the
corresponding video is played. This approach raises another question:
can you change this parameter (Audio desynchronization compensation)
programmatically in a plugin, without involving the user?

 

Any suggestions will be welcome.

 

Thanks in advance,

Mikel Astiz

 

 

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