Plex Skipping forward by a few seconds on Web Player

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Okay, updates. It’s possible there are multiple bugs being discussed in this thread. I’ve been working to understand the behavior captured in this screen recording.

Hardware accelerated video decoding and network configuration aren’t contributing factors to the skipping forward.

Micro stalling to buffer looks similar but doesn’t jump the user forward.

Steps to address?

We’re doing 2 things:

  1. Our 4.34 release of Plex Web, coming next week, will have a new experimental setting to change how Plex Web handles direct stream and transcode video playback.
  2. Further investigation is required to identify the true source of the bug. The experimental workaround will be removed once we’ve addressed the core issue.

4.34 will be available on https://app.plex.tv first. It will arrive in the Plex Web version bundled with PMS at a later date. The setting can be enabled by:

  • Click on the Settings icon in the Plex Web header
  • Click Show Advance within the Settings view
  • Click on Debug within the Settings view left-side bar
  • Within the settings view you’ll see a Use alternate streaming protocol for video playback checkbox
  • Check that checkbox, save settings

In the meantime…

Best option is to use Firefox, Plex for Windows or Plex for Mac for playbacks until 4.34 arrives.

Disabling Direct Stream in Debug settings or converting your media to be directly playable is a valid but less pleasant workaround.

What’s the bug?

You can download two 60s videos that reproduce the issue. In our testing this bug:

  • is limited to direct stream playback in Chromium based browsers.
    • This bug wouldn’t affect direct play.
    • It could affect transcoding but so far I’ve been unable to repro
    • It’s not possible that this bug affects Plex for Windows or Plex for Mac
    • Arrived in/around Chrome 71
  • causes skipping forward during playback. The skips can < 1s or multiple seconds.
    • skip-batman.mkv video above has a 12s skip at the beginning followed by 5 more smaller skip forwards.
    • skip-avengers.mkv has multiple small jumps forward.
  • doesn’t affect every video.

Affected videos are not being buffered correctly by Chrome. Browsers buffer data in ranges; each is defined by a start and end time. Chrome should buffer 5 second non-overlapping continuous segments. Videos affected by this bug are not buffering continuous segments. Instead there are gaps in the browser’s buffer. Our player sees this gap and skips forward over it.

The skip forward behavior is typically good. Playback would otherwise halt waiting for data that may or may/not buffer. Regardless, skipping forward should be a rare occurrence.

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