Recording and displaying a live video feed and pausing the recording during silence

Cameron Blomquist cameron at
Tue Apr 26 12:52:51 UTC 2022

For context, I've been tasked with digitizing too many tapes.

I'm using gstreamer-rs to record the video and audio input from a UVC 
capture device. I'm also displaying the video stream so that I can 
monitor it for whatever issues might arise. When there are gaps in the 
video, I want to be able to pause recording while still displaying the 
stream. My pipeline looks something like this:

"splitmuxsink name=sink location=video%04d.mp4 async-finalize=true
mfvideosrc name=vsrc ! tee name=t
t. ! queue ! rsvgoverlay name=overlay ! queue ! autovideosink
t. ! queue ! valve name=valve ! videoconvert ! x264enc key-int-max=10 
tune=zerolatency ! queue !
wasapisrc ! queue ! audioconvert ! removesilence remove=true 
silent=false ! audioconvert ! audioresample ! opusenc ! queue ! 

I monitor the pipeline bus for messages from removesilence to split the 
video. On silence_detected, I emit split-after to the splitmuxsink and 
open the valve and update rsvgoverlay. On silence_finished, I close the 
valve and update rsvgoverlay to show that we are once again recording. I 
use a ctrlc handler to send EOS to the pipeline.

You can probably see where this is going. When I open the valve, the 
entire pipeline freezes. I can't even quit the program with Ctrl+C since 
the EOS is dropped. If I don't do something to prevent frames from 
pushing into the splitmuxsink though, I'll end up with long periods of 
blank screen in the video files.

I also tried using output-selector into the splitmuxsink and a fakesink, 
doing something along the lines of

for pad in vselect.iterate_pads() {
     let pad = pad.unwrap();
     let elem = pad.peer().unwrap().parent_element().unwrap();
     if == "sink" {
         vselect.set_property("active-pad", pad);

on the removesilence messages to swap the pads. Interestingly enough, 
this also immediately freezes the pipeline in the same way that valve 
does and it also appears to drop the EOS event so that the pipeline runs 
forever. It might actually just be hanging somewhere since I don't 
receive clock messages either and I would expect to see NewClock when 
starting the pipeline.

Email threads from ten years ago describing similar issues with valves 
didn't provide much help that was relevant to how my pipeline is set up, 
so I am unsure of how to properly tackle this problem. The only 
recommendation I remember was to manually swap out pads, but I would 
have expected output-selector to be equivalent.

And this doesn't even touch on the potential issue of timestamps between 
those separate video files. Please tell me that splitmuxsink will handle 
that automagically.

Sorry to ramble, I tend to do that. How should I approach pausing the 
splitmuxsink to avoid recording dead air?

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