Why can't Plex play an MKV

[PHerzfeld]

Server Version#: 4.12.3
Player Version#: Apple TV 4k (latest)

Just wondering why Plex can’t seem to play a UHD MKV file on from my Ready NAS to my Apple 4k even though VLC can play it (from same source to same destination) just fine. I get an error that the server is not powerful enough to transcode BUT the file shouldn’t need transcoding - the internal format is h.265 (I’ve also tried h.264) and is compatible natively with the Apple 4K - as using VLC has established. Soooo… it “seems” like Plex is trying to transcode the MKV format simply because the file extension is MKV instead of “m4v” or “mp4” rather than determine the internal format in the MKV package… When I convert the file to m4v (still UHD) plex can play it fine (though I lose subtitles…)

[nibbles]

That should work, H.265 is fine, 4K is supported. Things that can cause transcoding are often subtitles and settings that disable Direct Play.

If your H.265 has only SRT subtitles embedded as one of the tracks, you’re most likely to have success.

There’s a 4K FAQ which will cover topics like this if you want.

[nickest1981]

im having the same problem. my plex will play some mkv’s but not others any solution for this?

[nibbles]

@nickest1981 your goal would be to determine which ones play and why. Start a new thread for yourself and document it there. You will get some general troubleshooting tips from the thread:

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[basilh]

A number of conditions need to be met to avoid transcoding. Unless ALL the boxes are ticked, transcoding will happen. For more info, refer to this article.

Streaming Media: Direct Play and Direct Stream | Plex Support

When transcoding does happen, you then hit off-the-shelf NAS limitations. NAS devices generally don’t have powerful processors (and are RAM limited) required for transcoding.

NAS Devices and Limitations | Plex Support

[darcilicious]

You can get see exactly why it’s transcoding if you go to Server Settings / Dashboard and look at the Now Playing section:

Server Status and Dashboard | Plex Support

[PHerzfeld]

Thanks to everyone who replied, I appreciate the articles and ideas… Some additional notes;

1. I have difficulty getting the dashboard activity to show what’s happening because it errors out and stops before I can get to it (player and server on different floors in the house). I have enabled debug logging so hopefully will glean some more info and will share what I can.

2. While I understand that the files are being transcoded I’m trying to understand WHY. I can play the exact same physical file from the same NAS server thru the same appleTV 4k on the same TV, across the same gigabit hardwired network using the VLC app and it plays just fine. Subtitles & all. But when I play it thru Plex it get’s transcoded - unnecessarily (with or without subtitles) and the server is not powerful enough to transcode 4k. I have tried using handbrake to encode the files into a variety of compatible formats (frame rates, h.265, h.264, HEVC, lower bit rates, AC3 audio, AAC audio, etc.) and they all result in transcoding. However, when I encode in to MP4 or M4V instead of MKV then Plex plays the files without transcoding (but I lose subtitles).

That would “seem” to be a bug or deficiency in Plex’s ability to match source file compatibility with device that makes it work much harder than it needs to…

hopefully the debug logs will tell me more about what is triggering the transcode or what it “thinks” is incompatible.

[nibbles]

Plex has a name for not transcoding things, it’s called Direct Play, and there are ways it can be disabled, which would cause a transcode.

Plex has a name for videos that are in an acceptable encoding but the wrong container for a player, for example a TV that requires MP4 but you have MKV, that would be adjusted with the feature Plex calls Direct Stream. It just repackages the mkv into an mp4 in that case.

You want your player and server to be setup with words like Original Quality or Automatic or Highest which are the terms used in some of the Plex settings. Another obvious one is the checkbox for Direct Play and the checkbox for Direct Stream. You might need to Settings > Show Advanced to see those two checkboxes.

I once had a user who had accidentally changed his setting away from Original Quality, and all he needed was to put that back.

It’s worth looking at. If you post your logs, we can dive into it more.

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In an effort to help troubleshoot an issue you post about, you may be asked to post your log files. While posting your logs in the forum is optional, some issues cannot be investigated without logs to review. It may be difficult or impossible for the community to help you without your logs. We respect your privacy and want to ensure you are fully aware of what kind of personally identifiable information may be contained in your log files, so you can make an informed decision that best suits your…

https://support.plex.tv/articles/201869908-log-files

[PHerzfeld]

Thanks Nibbles.

I have did (and do) have Direct Play" enabled (checked) and Direct Stream enabled (checked). I have also used the player settings on the AppleTV app to ensure that “original quality” is selected so I have to think it’s something about the encoding of the 4k files.

[darcilicious]

@PHerzfeld

I can play the exact same physical file from the same NAS server thru the same appleTV 4k on the same TV, across the same gigabit hardwired network using the VLC app and it plays just fine

Plex is not VLC and there’s no point in comparing the two. Getting 4K/HDR Files to play on the Apple TV requires specific type of video/audio files, especially if you’re not using the enhanced player (available only to Plex Pass users).

[TeknoJunky]

@PHerzfeld

difficulty getting the dashboard activity to show what’s happening

since you don’t have plex pass, the dashboard is fairly limited, even if you were not getting errors.

you might search for ‘tautulli’ which is a 3rd party app which will provide a nice monitoring interface of plex, but separate from plex.

[collinsromeo479_yandex_com]

MKV is not as compatitable as MP4, many video players such as Movies & TV app, Windows Media Player, Media Player Classic don’t work with MKV files properly. And there some solutions FYI:

Fix 1: downloaded MKV codec like K-Lite, CCCP codec, or use the MKV-compatible video players like VLC.
Fix 2: enable the hardware acceleration on your HD video player
Fix 3: use a free video converter to convert MKV to MP4 as MP4 could be played on any media players and devices without installing codecs.

[DaveBinM]

The first two fixes don’t really have anything to do with Plex, or help to solve the user’s issues. Additionally, our enhanced player on Apple TV does support MKV containers, however, it is currently only available as a preview to Plex Pass users

[PHerzfeld]

Thanks Dave. I’ll try the preview to see if it fares any better. I would consider converting the MKV’s to MP4’s (or M4v’s) but I haven’t figured out how to consistently get subtitles to be an “option” (as opposed to permanently burning them in) when using the MP4 format. Also, soundtracks are more limited using the mp4 format.