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Posted by Donna Peng - Contact Author

[Fixed] Plex Can't Read/Play MP4 Files Error

Are you still in a love-hate relationship with Plex media player? You have to confront the reality: the highly sought-after Plex remote media streaming and video playback features you love come at the cost of varied types of Plex errors. You've just solved problems like Plex server settings unavailable issue, remote access not working, Plex subtitles not working...Unexpectedly, when you load Plex supported MP4 files to Plex media player, another issue you never thought about occurs - Plex can't read some (if not all) MP4 files.

Can't get why? Why some MP4 files are okay with Plex while others are declined by Plex? After all, MP4 is on the paper of Plex supported formats. That being said, it's still complicated when it comes to the actual movie playback in Plex. Reasons aside, let's have a look at the specific solutions first:

Some MP4 Files Can't Play on Plex? Check Solutions↓

Solution 1: Upgrade or Downgrade DSM

If your Plex media server is running on Synology Nas, upgrade the DSM (DiskStation Manager) on your NAS or downgrade it to have a try.

Solution 2: Disable Direct Play and Enable Transcoding

Plex has a built-in video transcoder - Plex Universal Transcoder. Access to your Plex settings, disable Direct Play and turn on Plex transcoding to get the unplayable MP4 files automatically converted to your Plex client device best format.

Solution 3: Transcode MP4 and Adjust Parameters

Though MP4 is on the list of Plex supported formats, your MP4 file still can't be accepted by every client device because of MP4 video codec, bit rate, resolution, frame rate, audio codec, etc. Yes, you can use Plex built-in transcoder to convert MP4 video, but the transcoding speed would be snail's pace, especially simultaneously for a couple of Plex client devices. The common case is Plex buffering during transcoding for several clients at high resolution like 1080p, let alone 4K Ultra HD.

The better solution is to use an external video transcoder - WinX HD Video Converter Deluxe. With Level-3 GPU (Intel QSV/Nvidia/AMD) hardware acceleration tech, this tool enables you to bulk transcode MP4 files to Plex best settings (MP4 MPEG4/H264 or HEVC codec, 1920Ă—1080, 20Mbps, 30FPS, audio codec AAC, AC3 or EAC3) at GPU hardware accelerated speed without subscription fee. It can also compress 4K to 1080p/720p, lower 60FPS to 30FPS, adjust bit rate, change audio codec, convert any video to MP4, MKV, AVI, MOV, WMV, iPhone, iPad, Android, Microsoft devices, Xbox, PS5/4, etc. for movies/TV shows playback on any Plex client device without repeated transcoding, CPU overuse, Plex buffering errors.

How to transcode video to Plex supported format?

Step 1. Launch this Plex video transcoder after downloading. Click + Video button to load MP4 files.
Step 2. On Output Profile panel, choose a format that Plex supports, such as MP4, MOV, MKV... profile under General Profiles. Alternatively, you can choose a profile based on which client device you are using. WinX has optimized profiles for iPhone, iPad, PS5, Xbox One, etc.

Step 3. Click the setting button to specify resolution, bit rate, frame rate, audio codec, etc.
Note: though some MP4 video codecs are on paper, they might have produced faulty behaviour during development or testing and were subsequently disabled). You can manually change the video codecs based on your Plex client device, or just choose preset profiles for devices like iPhone iPad, Android Samsung, Huawei, Sony, Surface Pro, Google Pixel series, game consoles with best parameter settings.

Adjust MP4 video audio parameters for Plex
Adjust MP4 video audio parameters for Plex

Step 4. Hit RUN to begin Plex transcoding. Intel/NVIDIA/AMD hardware accelerator is enabled by default to boost decoding and encoding speed. Once finished, you can add the new file to Plex for Direct Play on as many devices as possible without repeated transcoding.

Solution 4: Re-name Your MP4 Files

MP4 files tote metadata (name/title). Plex Media Server will read the metadata embedded in the MP4 and override what it has from the file name. Providing confusing/bad names are living within MP4 files, they will mislead PMS or let PMS crap out in name identification. Therefore, with MP4 media files, you need to pay close attention to embedded metadata (title, name, etc). To name MP4 series, do as this naming method, e.g., The Big Bang Theory (2019) - S12E01 - title.mp4 (S12 refers to season 12; E01 means episode 1; delimiter might also be a full comma). If you have renamed in-place, perform the Plex Dance:
4.1. Copy to clipboard.
4.2. Move MP4 media to a different folder that Plex doesn't monitor.
4.3. Update Plex library and then empty trash.
4.4. Move back after bundles clean is finished.
4.5. Update libraries and scan again. PMS will see and pick up your MP4 files once the names are correct.

If renaming is complex to you, try this tool to help you - FileBot.

One article can't cover all the effective solutions. If you have better workarounds, you're warmly welcomed to contact us and share with us. We'd like to update this article with your precious ideas.


author - Donna Peng

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Donna Peng's fascination with multimedia began at an early age - shortly after she licked the physical disc and then she's been obsessed ever since. Her decade-long career at Digiarty after the graduation has seen her unmatched expertise in the field of DVD, digital video, software and anything related to home theatre. She is currently fascinated with photography.

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