[vlc-devel] Video Filter Input Buffering

Rémi Denis-Courmont remi at remlab.net
Thu Feb 11 22:36:15 CET 2016

On Thursday 11 February 2016 15:46:57 Darrell Walisser wrote:
> I have something that mostly works and will perform well enough to be
> useful, however there are a few issues remaining. The main problem is that
> I can't achieve a buffer on the input, while also being able to supply
> valid output, specifically the output date/pts on the returned pictures is
> before  the input picture due to buffering in the subprocess.

Depending on which filter chain the filter is running in, I reckon that the 
pictures are filtered either right after the previous picture was displayed, 
or right before the picture is rendered. Either way, the filtering latency 
must be less than one frame interval.

I believe this is meant to preserve interactivity/responsiveness.

> Initially, it seemed possible to return a NULL picture for the first few
> pictures, until some output pictures were available. This appears to "work"
> in the sense that the output is displayed, however it comes late in terms
> of the pts, the message from the video output is "Unsupported timestamp
> modifcations". Even if I could somehow supply correct pts, I assume it
> would be "late" and have to be dropped from the vout's perspective.

I think so.

> Maybe someone has an idea how to do this or what modifications to VLC would
> be needed to pull this off? Besides my use case it might be a good feature
> since filters could process several frames in parallel instead of being
> single-threaded.

I keep failing to estimate my own effort with any useful accuracy. Don´t ask 
me to estimate somebody else´s.

Rémi Denis-Courmont

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