Plex Buffering: Common Causes and Quick Fixes

If you use Plex to watch content, you may have run into moments where the video pauses frequently to load. These Plex buffering issues can be incredibly frustrating when they happen often, making it hard to enjoy what you’re watching.

This article explains the common causes of Plex buffering and offers practical fixes to help you restore smooth streaming. Read Diego’s Guide to Setting Up Plex Media Server for a more general guide to Plex.

Table of Contents

1. General Issues That Cause Plex Buffering
2. Plex Buffering Caused by Subtitles
3. Direct Play Buffering on Plex
4. Plex Buffering on 4K Videos
5. When Plex Keeps Buffering on a Local Network
6. Frequently Asked Questions
7. Final Thoughts

1. General Issues That Cause Plex Buffering

To resolve buffering problems, it’s essential to understand their common causes. Buffering in Plex can be broken down into several general categories:

a. Network-Related Issues

• Slow Internet Connection: If your internet speed isn’t fast enough to stream high-quality videos, Plex may struggle to deliver the data.
• Network Congestion: When multiple devices use the same network, it can slow down the data transfer rates available for streaming. 
• Misconfigured Router:  Some settings, like Quality of Service (QoS), can affect how your network handles streaming traffic. 

b. Server-Related Issues

• Hardware Limitations: Buffering will likely occur if your device running the Plex Media Server isn’t powerful enough. This is extremely common on low-end NAS devices.
• Server Configuration: Inappropriate transcoding options or misconfigured cache settings are another common cause of Plex buffering. 
• High Server Load: When several users try to stream content simultaneously, the server may struggle to keep up with the demand.

Tip: Instead of struggling with a home server, consider using a Seedbox to stream Plex. These powerful servers are often optimized for streaming, allowing smooth playback from any location.

c. File-Related Issues

• Unsupported File Formats and Codecs: In these cases, Plex may need time to transcode the file to a compatible format, which can be demanding on the server.
• High Bitrate or Large Files: These files require more bandwidth and processing power to stream smoothly. 
• 4K Files: High-resolution videos require significantly more data to stream than standard-definition or HD content. 

d. Client-Related Issues

• Device Incompatibility: Different streaming devices have different decoding capabilities, which can force the server to transcode the content, leading to buffering.
• Direct Play and Transcoding: Even if Direct Play is enabled, Plex may switch to transcoding if it encounters an unsupported audio format, resolution, or subtitle file. 

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3. Plex Buffering Caused by Subtitles

You may be surprised to learn that subtitles sometimes cause Plex buffering issues. This happens because some subtitle formats require rendering onto the video stream before delivery. As a result, the server will suffer additional load, potentially leading to buffering.

a. Differences Between Subtitle Formats

Not all subtitle formats are handled the same way in Plex. Common subtitle types include:

• SRT: SubRips are a text-based subtitle format that is generally easy for Plex to handle, as it doesn’t require significant processing. Most devices can support SRT subtitles without forcing transcoding.
• PGS: Presentation Graphic Stream subtitles are image-based, often found in Blu-ray rips, and require more processing power. This format typically forces the server to transcode the video.
• ASS: Advanced SubStation Alpha subtitles are text-based but support complex formatting, which can also trigger transcoding in some cases.

b. How to Fix Subtitle-Induced Buffering

If you experience buffering when using subtitles, try external SRT subtitle files. Most devices widely support this format and do not usually require Plex to transcode the video. If you have embedded subtitles, consider extracting them and converting them to SRT format.

You can also try adjusting options such as:

• Preferred subtitle format: Choose a format more compatible with your devices.
• Automatic transcoding preferences: Configure settings to reduce the likelihood of forced transcoding when subtitles are enabled.
• Enable burned-in subtitles only when necessary: Burned-in subtitles are rendered directly onto the video, which always requires transcoding. Limit this option to cases where it is unavoidable.

4. Direct Play Buffering on Plex

Direct Play is when Plex streams a media file from the server to the client device in its original format without any changes. This is ideal because it minimizes server processing requirements. However, for Direct Play to function, there are specific compatibility requirements:

These include:

• Video and audio codecs
• File container (file type)
• Resolution

The above must match the device’s capabilities where playback is meant to occur. 

Since Direct Play is desirable, fixing Plex buffering issues related to this primarily focuses on ensuring compatibility.

a. How to Fix Direct Play Plex Buffering Issues

If you frequently experience buffering with specific files, consider re-encoding them in formats fully supported by your client devices. For example, if your device supports H.264 video and AAC audio, converting files to this combination can help avoid transcoding.

Other tweaks to try:

• Enable or Disable “Allow Direct Stream”: In some cases, Plex may attempt Direct Stream (a combination of Direct Play and transcoding). Enabling or disabling this option can influence whether Plex performs partial transcoding or attempts Direct Play.
• Limit the Maximum Bitrate: This adjustment can prompt Plex to transcode high-bitrate files to a more manageable quality.

5. Plex Buffering on 4K Videos

Getting Plex to run 4K videos smoothly requires more bandwidth, processing power, and optimized settings. When these requirements aren’t met, Plex buffering can occur frequently. Understanding this can help you optimize your setup and reduce interruptions.

a. How to Fix Plex Buffering on 4K Videos

• Ensure Adequate Bandwidth: A minimum internet speed of 50 Mbps is recommended, with 100 Mbps or higher ideal. 
• Use Wired Connections: Wired connections provide more stable and consistent speeds than WiFi, making them better suited for handling 4K streams.
• Choose WiFi Wisely: If WiFi is unavoidable, connect to the 5 GHz band, which offers faster speeds than the 2.4 GHz band.

b. Optimizing Plex Servers for 4K

You can also tweak some options on the Plex server to improve 4K playback performance.

• Enable Direct Play: If your streaming device supports the video’s codec and resolution, enable Direct Play to avoid transcoding. 
• Maximum Bitrate Setting: Set a lower maximum bitrate for streaming. This will allow Plex to reduce the quality slightly to maintain smooth playback.
• Transcode 4K Content to Lower Resolutions: If your server is not powerful enough to handle 4K transcoding, consider creating lower-resolution copies.
• Hardware-Accelerated Transcoding: Some server hardware supports this, which can significantly reduce CPU usage and improve performance.

c. Upgrade Server Hardware if Needed

If your Plex Media Server struggles to transcode or stream 4K content, YOu may not need a new server. Instead, consider upgrading specific hardware such as:

• CPU: A modern multi-core processor with a high clock speed can better handle 4K transcoding.
• RAM: Increasing the RAM in your server can help manage larger files and improve transcoding performance.
• Hard Drive: One upgrade that’s often overlooked is the hard drive. Instead of focusing on capacity, ensure your hard drive is fast, preferably 7,200 rpm.

6. When Plex Keeps Buffering on a Local Network

Streaming locally should be smoother because the server and client device are on the same network. However, various factors can still cause Plex buffering even under these conditions. 

a. Diagnosing Local Network Buffering Problems

• Check Network Usage: Use your router’s management interface to see if other devices on the network are consuming significant bandwidth. 
• Test Different Devices: Try streaming the same file on a different device to see if the issue persists. 
• Review Server Performance: Check your Plex Media Server’s resource usage (CPU and memory) while streaming. 

b. How to Fix Plex Buffering on Local Networks

• Switch to a Wired Connection: Wired connections offer more stable and consistent data transfers. 
• Use a Modern Router: Ensure your router supports high-speed connections. Upgrading to a newer router may help if you use older networking equipment.
• Consider Mesh WiFi: If WiFi is unavoidable, ensure sufficient signal coverage. Larger homes may need a Mesh network for adequate coverage. 
• Configure QoS Settings: By prioritizing Plex traffic, you can ensure your streaming data gets the bandwidth it needs.
• Enable Direct Play: Ensure Direct Play is enabled in your Plex settings.
• Adjust Maximum Bitrate: Lowering the maximum bitrate setting for local streams can help if your network struggles to keep up.

7. Frequently Asked Questions

8. Final Thoughts

By understanding the underlying causes and how Plex handles streaming through processes like Direct Play, transcoding, and encoding, you can take targeted steps to optimize your setup. Most of the specific problems you may face can be traced to just a few vital areas.

By optimizing your setup in these areas, you can drastically reduce Plex buffering and any hiccups in your Plex streaming experience. Alternatively, you can try another media server like Jellyfin.

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