[vlc-devel] question: Can modules influence the presentation time?

kasper defusix at defusix.net
Sat Aug 22 23:56:24 CEST 2015

I have a question related to module development. I don't know if it's 
appropriate to ask it here, but I got no answer on #videolan on 
Freenode, and I can't find an active forum for VLC development

I have a ledstrip controlled by an embedded Linux computer. I want to 
develop a visualization module for VLC that sends data (based on the 
audio) over UDP  to that embedded computer. The issue is: Synchronizing 
the led visuals with the played audio. Because there will be some delay 
between the transmission of the graphics and the time it displays, I 
thought it would be best to let the module send frames including the 
presentation timestamp. (I will use PTP to sync the clocks of both 
systems, so the timestamps created by VLC will be usable by the embedded 
Linux computer). Looking at the source code of VLC, modules that process 
audio or video blocks get a PTS. My question is: Can the presentation 
time be delayed by a module in order to create enough headroom? The 
headroom I need will be about 8ms to 15ms.

If this is not possible, the only solution I can think of is having the 
module just buffer audio blocks, thereby delaying the audio. But it will 
get out of sync with the video then.

With kind regards,

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