measuring FPS of a source live stream (using identity elements)

[Nicolas Dufresne]

Le jeudi 16 mars 2023 à 17:43 -0400, Matt Feury via gstreamer-devel a écrit :
> hello all,
> 
> i am attempting to measure FPS of a source stream (e.g. rtsp or hls). I am
> currently using an identity element immediately after the source element (e.g.
> rtspsrc -> identity -> decodebin -> fakesink). Using the handoff signal on
> identity, I am able to get a good calculation of buffers per second.
> 
> However, it seems that this value is not always 1:1 with frames per second. It
> very frequently is on stable streams (e.g. I often see 29-31 buffers/sec on a
> 30fps stream). However, on streams with intermittent connectivity, it doesn't
> seem to tell the whole story.
> 
> I've seen fpsdisplaysink which actually works really well (I am able to see
> "real" fps values that are dynamically changing as the pipeline plays).
> However, a) I don't want to measure the fps at the sink (i have a tee'd
> pipeline with multiple sinks and more interesting in measuring source fps than
> that of my pipeline) and b) this element seems to just overlay it – ideally i
> would be able to get the average "recent" fps as a property.

Just set sync=false on fps display sink, and it will include the source jitter.
I strongly recommend using fakevideosink for that, as it will avoid software
copies with HW decoders.

> 
> I've seen ridgerun's gst-perf element, but that only seems to log values.
> 
> Is there a recommended approach to monitoring "real" FPS of an incoming live
> stream? Ideally using identity, but open to other options.
> 
> Thanks,
> Matt

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