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QtMultimedia video buffer settings

  • I wrote myself a QML / QtMultimedia app that streams video from the internet. My app works perfectly fine under Ubuntu 20.04. Compiled using the exact same Qt SDK under Arch Linux, it also works, but the videos start up after a significant delay in comparison, there are delays when seeking in the video, and the video sometimes pauses entirely after seeking. Seeking again will make it play fine again.

    I'm ruling out Qt related issues because the very same app works perfectly fine under Ubuntu. I don't really know much about gstreamer (Linux multimedia backend), so I don't know which direction to go to even start debugging this. My guess is there is some default video buffer configuration, probably much higher on ArchLinux, hence it takes longer to fetch enough to fill the buffer, but I don't know how would I go about fixing or customizing this buffer size. Any ideas?

    Some technical info:
    Qt 5.15.2
    Ubuntu: gstreamer 1.16.2
    Arch: gstreamer 1.18.5, I also tried 1.19.3 (git)

  • You are probably on the right track. Generally streamer packages have options to set the cache fill before playing. mplayer -cache is the one I'm most familiar with. I'd guess that the defaults are different based on the use of two different linux distros. Search the gstreamer docs, looking for the config file location and caching parameters. look at the dpkg info for gstreamer to see what the default config file is for the package on each distro and investigate there.

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