[Bug 747558] New: gsthlsdemux.c/gstadaptivedemux.c: Possible Improvement: Variant selection doesn't consider hysteresis

[GStreamer (GNOME Bugzilla)]

https://bugzilla.gnome.org/show_bug.cgi?id=747558

            Bug ID: 747558
           Summary: gsthlsdemux.c/gstadaptivedemux.c: Possible
                    Improvement: Variant selection doesn't consider
                    hysteresis
    Classification: Platform
           Product: GStreamer
           Version: git master
                OS: Linux
            Status: NEW
          Severity: normal
          Priority: Normal
         Component: gst-plugins-bad
          Assignee: gstreamer-bugs at lists.freedesktop.org
          Reporter: dguthrie at digisoft.tv
        QA Contact: gstreamer-bugs at lists.freedesktop.org
     GNOME version: ---

When the average bitrate is calculated, this resultant bitrate (when multiplied
by bitrate_limit) could be very close to a variant in the m3u8 playlist file.
Which could result in the variant selection oscillating between two different
variants after each segment is downloaded. In any system which make a decision
based on an input switching an output based on the inputs magnitude, it is
normal to add hysteresis to the calculation as this will prevent random noise
from causing instability. The instability in this cause would be the viewer
being able to observe frequent changes in variants when playing back video.

A hysteresis variable could be added to the final bitrate value used to select
the variant from the playlist. This variable is set to -50kbps when changing
download a variant and set to 0 when changing up a variant. This would allow
for 50kbps of noise in the final bitrate calculation which would not influence
the variant selection when the download rate is near constant.

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