Possible causes for Stuttering, Juddering and Stalling playback [2010-11-23]
Step 1 - Check this post and make sure you have the latest version of Plex and any Hot-fixes installed.
Step 2 - Check this list for the best description of your problem.
When the audio track and video track are not matching up, resulting in (most noticeable) mouths moving and the dialog not matching the facial movements.
When a television doesn't refresh quickly enough or doesn't stitch frames properly resulting in a "hopping" motion when panning left to right or experiencing fast motion. Judder is almost always at perfectly regular intervals, its not a random stutter, but rather a regular skip every x seconds or whatever, in medium to high motion scenes.
When audio continues, but frames are dropped, resulting in a pause, then a speed up of frame rate to catch up to the audio track. Stutter can be caused by CPU starvation - which can be more subtle. You may see dropped frames in the 'Info' overlay when playing video. To drop down the overlay, press 'i' whilst playing a video.
When your network cannot keep up with the video file and the playback stops all together, then rebuffers to proceed. This results in a total pause of video/audio playback, then resuming.
Step 3 - Check through the list of possible causes for your problem. We recommend you check each of the items, even if you're 100% sure that "this is not the cause of the problem". The exception to this is when faced with a Mac OS X downgrade as that is a certified Pain in the Behind.
Recap - Stutter playback is a non-regular pause in playback - like your Mac is running out of steam, then catches up. If you're seing a regular pause, check the 'Judder' section.
Other Applications Running
Playing HD media is demanding of your computer's resources. Make sure Plex and the Plex Media Server are the only applications running - and we really mean, No Other Apps/Utilities/Widgets Running. A good way of checking this is to open the Activity Monitor and look for any applications that are using CPU cycles or driving disk activity. You may have installed a background app that is eating away at your system's resources.
Mac OS X Preferences
Desktop Picture Changing can cause periodic stuttering when the picture change is occurring. Disable this option. Mac OS X Preferences > Desktop & Screensaver > Desktop > deselect, 'Change Picture'
Plex Media Server Scanning frequency
Plex Media Server will periodically scan your library for new and changed media. This scan can tax both CPU and Hard Drive. Either set scanning to 'Manual' or daily:
- Click the PMS icon '>' in your Mac's menu bar, choose Preferences
- Choose Library
- Deselect "Update my library when changes to my folders are detected"
- Select "daily" or Deselect "Update my library" to update the library manually. Manual update is done by Plex '>' icon > Update Library
DTS-HD or MA, Dolby Digital TrueHD Audio Tracks
These tracks will cause stuttering playback. There is currently no work-around this other than to re-encode the tracks to standard DTS/AC3.
H.264 Hardware Acceleration
Some users - particularly with Mac Mini 2009/2010 models - have reported stuttering playback with H.264 coded media and Hardware Acceleration enabled in the Plex Client. Some users have also reported issues with Mac OS X 10.6.4 and Hardware Acceleration. To check this possibility:
- Disable H.264 Hardware Acceleration in the Plex Client. Plex > Preferences > Video > Player > disable H.264 Hardware Acceleration and test playback
If playback is good with H.264 acceleration disabled and you really want to try enabling H.264 Hardware Acceleration:
- Upgrade to Mac OS X 10.6.5, enable H.264 Acceleration and test playback. If playback is good, you're done.
- If playback is still stuttering, downgrade your Mac to Mac OS X 10.6.3 and test playback again.
- If playback is still stuttering, disable H.264 Hardware Acceleration and continue with other options here.
Alternate skin selected for the Plex Client
It has recently been identified that using Plex Client skins with animations such as 'Rotating Backgrounds' can cause a periodic stutter. If you're seeing a stutter every (say) 15-20 minutes, and are using a skin other than the default MediaStream skin, try switching back to the MediaStream skin and test playback
Recap - Judder is pauses in playback that are regular and consistent. Judder is fundamentally due to a mis-match between the media being played and the frequency the TV is set to.
Judder is a relatively easy issue to identify but not so easy to eliminate. There is a long technical explanation for judder which will be covered in the Wiki shortly. The quick explanation is that a movie file coded at 24fps best played on a TV set to 24 or 120Hz. If not, the mis-match between the movie's fps and the TV's refresh will cause Judder. It will be regular - and depending on the mis-match either very subtle or quite jarring. To identify this issue:
- Find a movie that shows judder
- Analyze it in MediaInfo
- Identify the fps
- Set your TV to the same or as close to the same or multiple of the fps. For example, a 25fps film will play best on a TV set to 50 or 100Hz
- Play with the settings available in the Mac OS X Display preferences for your TV
Here is a table that will help:
Often, TV's will feature 'Motion Smoothing' features that 'help' with some media playback. These features add complexity when trouble-shooting issues and are best disabled. If your TV has these features, please disable them whilst diagnosing playback issues.
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