A buddy called me last winter, furious that his brand new Synology DS224+ was "garbage" because every movie stalled two minutes in. He was ready to return it. Twenty minutes on the phone and the buffering was gone, and he had not touched the NAS once.
The problem was never the box. It almost never is.
Buffering is one of those symptoms that sends people shopping for new hardware when the actual cause is a setting, a cable, or a wrong assumption about how their gear talks to each other. I have fixed this exact complaint dozens of times, and the same handful of mistakes come up again and again. Here they are, along with how to tell if you are the one making them.
Mistake 1: Blaming the NAS when the network is the real bottleneck
The single most common error is assuming the NAS is too weak. In reality, a 1080p movie streams at roughly 8 to 20 Mbps, and even a 4K remux tops out around 80 to 100 Mbps. Any NAS from the last decade can read a file that fast in its sleep.
What usually cannot keep up is the path between the NAS and your TV.
The first time I hit this myself, my old ReadyNAS was fine over ethernet but stuttered constantly to the living room. The culprit was a $12 unmanaged switch that had quietly negotiated a 100 Mbps link instead of gigabit. One bent pin in the cable did it.
Mistake 2: Streaming 4K to a device over WiFi and hoping
WiFi is where most buffering complaints actually live. A wired connection gives you a steady, predictable pipe. WiFi gives you a number that looks great on paper and collapses the moment your neighbor's microwave, a thick wall, or a phone downloading updates gets involved.
I see this constantly with people trying to push a 60 GB 4K file to a Fire TV Stick sitting behind the television, jammed against a metal stand, three rooms from the router.
A 2.4 GHz WiFi link in a busy apartment might give you a real-world 15 to 25 Mbps despite advertising far more. That is fine for 1080p, hopeless for high-bitrate 4K.
Mistake 3: Forcing transcoding when you could be direct playing
This is the mistake that catches the most people, and it is worth understanding properly. When your player can read a file's format natively, the NAS just sends the file as-is. That is called direct play, and it is nearly free on any CPU.
Transcoding is when the NAS has to rebuild the video on the fly into a format the client understands. That is enormously more work.
A dual-core Celeron in a budget NAS can direct play a dozen streams and struggle to transcode even one 4K stream in real time. When it falls behind, you get buffering while the CPU frantically tries to catch up.
What quietly triggers transcoding
- Subtitles burned into the picture, especially image-based PGS or VOBSUB formats
- An audio track your player cannot decode, like TrueHD or DTS-HD on a cheap streaming stick
- A bitrate limit set in the app that forces a downscale
- An unsupported container or codec such as older 10-bit HEVC on an aging device
In Plex, watch the "Now Playing" dashboard while something buffers. If it says Transcode instead of Direct Play, you have found your answer. The Plex documentation on direct play and direct stream explains exactly what each mode does.
Mistake 4: Ignoring the CPU your NAS actually has
If you genuinely need to transcode, for example remote family members on slow connections, the chip inside your NAS matters a great deal. Not all NAS CPUs are equal, and the marketing rarely makes this clear.
The magic feature is hardware transcoding, sometimes branded as Intel Quick Sync. A model with a Quick Sync-capable Intel chip can transcode several 4K streams while barely warming up. An ARM-based or older Celeron model without it will melt trying to do one.
| NAS type | Example CPU | Realistic 4K transcode |
|---|---|---|
| ARM budget model | Realtek RTD1619B | None, direct play only |
| Older Intel Celeron | J4025 (no Quick Sync tuning) | 1 stream, marginal |
| Modern Intel with Quick Sync | Celeron N5105 or better | 2-3 streams comfortably |
Mistake 5: Putting the media library on a failing or half-asleep drive
Every so often the buffering really is the storage, just not the way people expect. A single drive that is starting to fail will read fine for most files and then hang for several seconds when it hits a weak sector. That reads as a pause mid-movie.
The other version is aggressive power saving.
If your NAS spins its disks down after 10 minutes of idle, the first few seconds of playback stall while the drive spins back up. I have watched people chase network gremlins for a week when the fix was disabling HDD hibernation in the power settings.
Check your drive health in the NAS dashboard. On Synology it lives under Storage Manager, and a rising reallocated sector count is a warning sign worth acting on. Backblaze publishes real-world drive failure statistics that are genuinely useful when you are deciding whether a nervous-sounding disk is worth replacing.
Mistake 6: Running everything through a VPN or the internet by accident
This one surprises people. If your streaming app is logging in through Plex's relay servers instead of connecting directly to your NAS on the local network, every byte takes a detour through the internet and back, capped at a slow relay speed.
You are on the same WiFi as your NAS, and yet the video is crawling through a data center two states away.
It happens when remote access is misconfigured, when a device VPN is left on, or when the app cannot find the local server address. In Plex, a green "indirect" or a relay warning in the server settings is the tell. Fixing the local connection or setting a static IP for the NAS usually clears it instantly.
How to find your specific culprit in five minutes
You do not have to guess which mistake is yours. Work through it in order and you will corner the problem fast.
- Play the file on a wired device. Perfect? Your issue is WiFi, not the NAS.
- Open the server's activity dashboard. See "Transcode"? Fix the format or client, not the hardware.
- Check the network interface speed. 100 Mbps means a cable or switch problem.
- Look at drive health and disable disk hibernation.
- Confirm the client is connecting locally and directly, not through a relay or VPN.
Nine times out of ten you will stop before you reach step four.
Where this leaves you
My friend with the "garbage" DS224+ still uses it every night, three years later. His actual problem was mistake two and mistake six stacked together: a 4K file, a WiFi stick, and a relay connection all fighting each other.
The lesson I keep coming back to is that buffering is a communication failure between your gear, rarely a raw power failure inside the NAS. Chase the path the video takes, not the price tag on the box. Once you learn to read the activity dashboard and check a link speed, you will diagnose these in the time it takes to make coffee, and you will stop buying hardware you never needed.
Frequently asked questions
Why does my NAS buffer only on 4K files but not 1080p?
4K files carry roughly 4 to 10 times the bitrate of 1080p, so they expose weak WiFi links and transcoding limits that 1080p hides. If 1080p plays fine and 4K stalls, test the same 4K file on a wired device. It usually points to WiFi or forced transcoding rather than the NAS itself.
How do I know if my NAS is transcoding or direct playing?
Open your server's activity or Now Playing dashboard while a file buffers. Plex, Jellyfin, and Emby all label the stream as Direct Play, Direct Stream, or Transcode. Transcode means the CPU is rebuilding the video in real time, which is the most common buffering cause on budget hardware.
Do I need a Plex Pass to stop buffering?
Not always. Plex Pass is only required to enable hardware transcoding, which matters if you must transcode for remote or incompatible devices. If your clients can direct play your files, you will get smooth playback with no subscription at all.
Can WiFi really cause NAS buffering if my speed test looks fast?
Yes. A speed test to the internet does not measure the local link between your player and your access point, and WiFi throughput drops sharply with distance, walls, and interference. A device showing 100 Mbps to the internet might only sustain 20 Mbps to your NAS over a congested 2.4 GHz channel.
Should I upgrade my NAS to fix constant buffering?
Usually no. Work through the network, WiFi, transcoding, drive health, and connection-path checks first. Most buffering is solved by a cable, a setting, or moving a streaming stick to ethernet, and a new NAS will buffer just as badly if the underlying path stays broken.
