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Does Plex Support MKV? How to Play MKV on Plex?

"Can Plex play MKV? I'm trying to play a UHD MKV file from my Ready NAS to Apple TV 4K via Plex. I got an error that the server is not powerful enough to transcode. But theoretically it doesn't need to be transcoded - the encoding codec is HEVC, which is natively supported by Apple TV 4K and Plex. What went wrong? How can I play MKV on Plex? "

As above, Plex MKV playback issue has been asked frequently, but there are still many people feel confused about it. Follow this article to find out why MKV playback fails on Plex and how to play MKV via Plex without transcoding.

Does Plex Support MKV? Why Is Your MKV Required to Be Transcoded?

Yes. Acoording to the plex.tv, MKV with the following video and audio encoding is natively supported by Plex.

  • Video encoding: H.264, hevc (H.265), mpeg4, msmpeg4v2, msmpeg4v3, vc1, vp9, wmv3
  • Audio encoding: aac, ac3, alac, e-ac3,flac, mp3
Plex MKV playback error

This means if your MKV is encoded with the above video and audio codec, it should be able to direct play on Plex. Given this, why your MKV file is still required to be transcoded? Why Plex not recognizing your MKV files? There are many situations that can lead to this issue, for example:

  • Your MKV is packed with soft subtitle streams.
  • You have turned off the Direct Play and Direct Stream option in Plex by accident.
  • The MKV video is not compatible with the devices that installed Plex media server.
  • The bit rate of the MKV is higher than Plex request.
  • Your MKV files are TV shows or series, which will not show in Plex library if you haven't renamed them correctly.

From above, subtitle is absolutely the most likely one for MKV transcoding on Plex. You know, MKV container is able to store video, audio and subtitle streams. That's why many people make their videos in MKV format. However, to play MKV on Plex, such subtitles need to be burned on the video. Even though your MKV file is compatibile with Plex, it is still required to be transcoded. Then you probably find the MKV transcoding process stucks and MKV fails to play owing to underpowered hardware, especially when you're trying to play MKV on Plex from NAS. Most NAS media are based on ARM CPU, which is not powerful enough to transcode 1080p, 4K videos.
Check the NAS devices and limitations for Plex transcoding >>

In this case, how can you play MKV files from NAS via Plex without transcoding? You can transcode your MKV files with a MKV converter in advance, and then add MKV to Plex for smoothly playback.

Convert Plex Unrecognized MKV Files to MP4 (with Subtitles) for Better Compatibility

First of all, you need a video converter which can convert those Plex incompatible MKV files to MP4 format and burn soft subtitles to the video. WinX HD Video Converter Deluxe is a nice option. It allows you to convert MKV to Plex highly compatible MP4 format in HEVC, H.264 with fast encoding speed and zero quality loss, as well as burn SRT subtitles to video easily. Besides, with this video converter, you can also convert various common formats to MP4, MOV, AVI, WMV, VP9, and more with 420+ optimized profiles, adjust video parameters like resolution, frame rate, bit rate etc., trim video length, crop video frame size and more.

How to Convert MKV to MP4 with Subtitles for Plex?

After free downloading and installing the WinX HD Video Converter Deluxe, fire it up on your computer.

Step 1. Click "+ Video" button to load the Plex unrecognized MKV files.

Step 2. Go General Profiles > MP4 Video (h264+aac) to choose MP4 as output format. Of course, HEVC is also a nice choice if your device support it.

Transcode MKV to MP4 for Plex

Step 3. Click Edit button, and choose Subtitle panel. Tick on the box of Enable Subtitle, also check on Inner box. Choose one of the subtitle to burn on the video. Learn more on how to edit MKV files >>

Burn subtitles to the video

Step 4. Tap RUN button to start conversion. If your computer configuration is high enough, Intel/NVIDIA/AMD hardware accelerator will be auto enabled to boost decoding and encoding speed. Once done, you can load the transcoded MKV files to Plex library for Direct Play without buffering/freezing.


author - Jack Watt

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Jack Watt is a sought-after editor at Digiarty. He is responsible for digital and multimedia world, delivering definitive video and audio related software reviews, enlightening guides, and incisive analysis. As a fan of Apple, Jack Watt also brings his experience to more readers and focuses on writing of the Apple ecosystem at large.

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