As a streaming media server, Plex can be used as a portable library in which you can stream your collections of high-quality movies, TV shows, music, podcasts etc. from your computer to any other device, or also, share them with your friends. Though Plex claims to support MKV files and let you view them from virtually laptops/desktops to phones to HDTVs, the mkv playing error comes from time to time. For example, Plex won't detect MKV files, or your MKV video does not show up in the library on your dashboard/tablet app, or you can't even add MKV files to Plex's media library.

Fix Plex Not Playing MKV File

In fact, nifty this server is, there are always real scenarios where the quality of your Plex experience is decreased due to the problem of video file incompatibility. And MKV playback issue is one of the most common problems. The following article shows you why Plex not working with MKV and offers a quick fix to troubleshoot Plex MKV not showing error.

Possible Reasons for Plex Won't Recognize MKV or Play MKV Files Smoothly

Why Plex won't recognize the MKV files while scanning library files? Actually, it can be caused by various reasons. To be specific, there's a number of potential scenarios how Plex not working with MKV and below are some of them.

1. Poor named MKV movies might have been matched as a different movie.

If random named MKV video not showing in Plex, you may find it in "rencently_added" column. In such a situation, make sure the whole file names were being recognized by Plex. For example, if all of mkv videos are all Sports videos so the names, there were kind of random. To solve it, you can set 'Scanner' as 'Personal Video Files Scanner' and 'Agent' as 'Personal Media'. Plex picks up pretty much any file with that setting. However, I found it's stuttering on when playing large 4K HEVC MKV files via Plex.

2. MKV files following the naming convention for multi-file movies end up as a single record in your library (e.g. Movie Name-part 1.ext and Movie Name-part 2.ext will result in an entry called Movie Name which will play both entries in sequence).

3. Depending on your library settings, movies might be automatically associated with a collection and only display inside that collection.

4. MKV format/codec is not supported or MKV media with higher bitrate or with soft subtitles

Checked everything OK but still encounter MKV playback issues? Why my MKV file is being transcoded by Plex? Feeling frustrated? Well, accoording 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

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:

① Your MKV is packed with soft subtitle streams.
② You have turned off the Direct Play and Direct Stream option in Plex by accident.
③ The MKV video is not compatible with the devices that installed Plex media server.
④ The bit rate of the MKV is higher than Plex request.
⑤ Your MKV files are TV shows or series, which will not show in Plex library if you haven't renamed them correctly.

Plex MKV Playback Error

Conclusion: From above, subtitle is absolutely the most likely one for MKV transcoding on Plex. MKV is a video container format which can 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.

MKV is a nice container for video libraries… but some devices or players do not support them via direct play in Plex, making MKV files not playing errors like skipping/dropping frames, stuttering, video lags, grainy image quality and even MKV not showing in Plex library. To avoid lousy matters such as choppy playback and regular buffering, you'll find that transcoding your video files to a suitable format is the most efficient way out.

100% Working Solution to Fix MKV Files Not Showing Up in Plex Library Error

- Convert Plex unrecognized MKV files to MP4 for better compatibility.

Transcoding MKV files to MP4 in advance for more widely support on Plex across desktops, laptops, TVs, and mobiles is a great idea. There is a long list of free and paid conversion programs and tools available. But if you do not want to be held back by slow processing and poor output quality, EaseFab Video Converter is there for you. This program is available for both Windows and Mac PC and it can cope with all MKV files with encoded video/audio streams.

As an excellent MKV video converter, EaseFab Video Converter can convert MKV to MP4, MOV, AVI, WebM, and 420+ profiles, transcodes HEVC MKV to H.264, DTS to MP3/AAC, and changes MKV video specifications like resolution (eg. 4K to 1080p), bit rate, frame rate etc. As for the video quality, don't worry too much. With the constantly updated conversion algorithm and the advanced high quality engine, it guarantees you the MKV file size will be compressed greatly without quality loss. Moreover, the mbedded hardware acceleration tech will invoke GPU encoding/decoding built in graphic cards, achieving up 30X faster video conversion speed to encode MKV to MP4 with HEVC/H264 codec.

Simple Steps to Convert MKV to MP4 for Plex

The step-by-step guide is almost the same on PC and Mac. Here we will take EaseFab Video Converter for Windows as the example.

Step 1. After downloading, install and run EaseFab Video Converter on your PC or Mac, simply drag and drop your unrecognized MKV files to the program. You can also click Add Video button to load your source MKV files. (Note: batch conversion is supported, so you can load more than one file to save time.)

Load MKV File(s)

Step 2. Click Profile (located below where your files are displayed) and select the format you want from the drop-down list. To convert MKV for Plex, just choose MP4 (encoded with H264 and AAC codec) from Common Video as the output format. Of course, you're able to transcode MKV to HEVC/H.264 without changing the MKV container, or directly convert MKV to iPad iPhone, Xbox, PS4, Android phones, Apple TV etc.

Select MP4 As Output Profile

Tech Details for Encoding MKV to Plex

The default setting works well. Of course, if you want to customize video and audio encoding settings, just click the Settings button to customize these settings. According to our multiple tests, it's recommend you to store your videOS in the lowest standard provided below to yield the best playback result for Plex streaming.

• Container: MP4
• Video codec: H.264
• Resolution: 720p/1080p @8Mbps
• Audio track: Stereo AAC @128Kbps
• Aspect ratio: 16:9

Tips: Hardware and speed of the internet may also influence streaming across devices.

Recommended Settings

1. You're not suggested to adjust the frame rate and aspect ratio, if not necessary.
2. Lower the bitrate to a lower level. For example, adjusting the original Normal quality to bitrates of around 1800-2000 is acceptable without noticeable pixellation.
3. Lower the resolution. Typical MKV files are 1920×1080 (1080p). Adjust the resolution to lower 1280×720 (720p) or higher won't make any quality difference.
4. To get the best possible output quality and smallest file size, you can also choose to convert MKV to HEVC MP4. It has 50% smaller size at the same quality. Please note that Plex's HEVC playback depends on the device you are playing on. For the most part the server will stream whatever the client is requesting. Of the devices I use, the Xbox One, Plex Media Player, and Plex for Samsung all can play HEVC content and the resolution will depend on the device.

recommended settings for plex streaming

Please note: Adjusting these variables have some effect on the re-encoded video quality. Remember the file size and video quality is based more on bitrate than resolution which means bitrate higher results in big file size, and lower visible quality loss.

Step 3. After everything is OK, hit the Convert button on the main interface to start converting MKV to MP4 for Plex.

The process will be finished soon. After the conversion, you can easily find the encoded MKV video clips in the destination folder by clicking Open button for playing and sharing to your other devices via Plex Media Server.

Final Words:

Plex is an ideal streaming server which will give you free access to videos, movies, DVD, Blu-rays, TV series at the go. To optimize your experience as a Plex user, the best workaround is to transcode your media files to [email protected]@AAC. To digitize your DVD/Blu-ray collections, convert ISO, Video_TS folder, BDMV folder and Plex unrecognized files like MKV, VOB, TiVo, you can adopt an one-stop media converter EaseFab Video Converter Ultimate for help.