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How to Fix Plex Not Playing MKV Files?

Plex stoppped playing MKV files

Since yesterday, Plex won't play any MKV files on any Plex application be it web, mobile, or PS4. It will play nice with anything but MKV. I know for a fact I updated my Plex Media Server yesterday, but it wasn't playing before the update and it won't play now. Not even sure what to do. I tried uninstalling Plex Media Server and reinstalling but it didn't help. I'm at a loss.

Plex not play MKV files

Plex makes it possible to enjoy all of your media in an easy-to-navigate interface whether in your room, the car or an igloo in Alaska. Plex recognizes just about any kind of video, music or photo format. However, when you play media with Plex on different kind of devices, Plex will perform different media solution for your devices.

Direct Play

If the Plex App installed on device tells the Server that it has capabilities that exactly match the file you want to watch, the file can be sent to the App exactly as-is, so the work done by the Server is almost zero.

Direct Stream

If the Plex App installed on the device tells the Server that it is capable of handling the video and audio streams in the source file, but it can't handle the file container (.mkv, .avi, etc), the Server will copy the streams into a new compatible container and send that to the App. There's a little more work required by the Server but not a lot.


If the Plex App installed on the device tells the Server it can't handle the video or audio in the stream at all, the Server will convert the incompatible tracks to a compatible one and send that to the App. This process is called Transcoding and does the following:
- Reads the incompatible audio or video track
- Resizes the video if it's too large
- Re-encodes the video to a compatible stream
- Reads the incompatible audio
- Re-encodes the audio to a compatible stream
- Sends the Transcoded results in a compatible format to the App

Sometimes, you may have problems when transcoding with Plex Media Server when the media analysis process go astray and not completed or the media is encoded in an odd way. To fix the bad media analysis, you can re-analyze the media using Plex Web App. As for oddly encoded media such as the MKV file mentioned above, you can fix it with the following actions:
- Confirm you can play or transcode other media
- Try a more standard setting for the encoder if you've tweaked them and re-encode the media
- Provide a sample of the video to the Plex engineers via the Plex forums

As the media transcoding process with Plex Media Server is very CPU intensive, in addition, the transcoding process will use temporary disk storage for the converted media, therefore, if your computer don't have a faster/better CPU, more RAM to add or your boot drive is very small, you are not advertised to perform the transcoding process with Plex Media Server. You can use a third-party video conversion app such as Pavtube Video Converter for Windows/Mac to convert MKV to Plex app supported file formats and then add the video to Plex Media Server. If your video file size is too large, you can also use the program to compress 4K to 1080p or 1080p to 720p to let it play smoothly on your device.

Besides MKV, the program also has the capability to transcode other incompatible file formats such as MP4, AVI, WMV, FLV, VOB, M2TSWTV, etc to Plex playable format.

How to Convert MKV for Plex App Playing on Different Devices?

Step 1. Import MKV video files.

Launch the program, click "Load file(s)" or "Add video" button to load the MKV video file you want to convert in your PC into the program.

Step 2: Choose proper output format.

Click "Format" bar, from its drop-down option, select to output "HD Video" > "H.264 HD Video(*.mp4)" that are supported by most devices Plex.

Step 3: Compress video file size for different device.

Click "Settings" to open "Profile" settings window, click "Size(pix)" to select 1920*1080, 1080*720 or smaller resolution according to your own situation.

Step 4: Begin the conversion process.
Go back to the main interface, click right-bottom "Convert" button to start MKV to device Plex app most compatible H.264 HD format conversion process.
When the conversion is done, click "Open Output Folder" button to pop out the folder with converted files, then add converted files to plex for playing with the Plex app on different devices.

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