I’m reorganizing my movie and TV show library and noticed that some files are MP4 while others are MKV. I want good quality, small file sizes, and wide compatibility with phones, TVs, and streaming devices. I’m confused about which format I should standardize on and whether it’s worth converting everything. Can someone explain the pros and cons of MP4 vs MKV for everyday use and home media servers?
I stopped trusting random “best format” advice after fighting with a smart TV for half an hour one night. Here is what shook out from a bunch of trial, error, and some reading.
MP4 and MKV are not video types in the way most people use the word. They are boxes. The box holds the video stream, audio streams, subtitles, and sometimes extras like chapters.
- MP4 is the safe box.
- MKV is the overstuffed box.
That is the whole story in one line, but here is how it plays out in real use.
MP4 in practice
What I see with MP4:
• Every phone I have used played it without complaints.
• Streaming sites expect it.
• Game consoles, smart TVs, cheap tablets, all of them usually like MP4.
The trade-off is features. MP4 supports multiple audio tracks and subtitles, but once you get into more exotic stuff, it starts to feel limited. You do not get the same level of “throw everything in here” flexibility.
If I want a file that “just works” on random devices, I save to MP4.
MKV in practice
MKV feels like someone said “put everything in one file and sort it out later.”
Things I have had in one MKV file:
• The movie in two resolutions.
• Three audio tracks: original, dubbed, commentry.
• Soft subtitles in multiple languages.
• Chapters to jump between scenes.
It is common for high bitrate movie backups and TV series for that reason. The downside shows up when you try to play one of these on older TVs, built-in car players, or cheap sticks. Some of those see an MKV file and either refuse to play it or ignore extra tracks.
Modern media players handle MKV fine. Old or basic ones often do not.
Converting MP4 ↔ MKV without wrecking stuff
People overcomplicate this. Here is what worked for me.
MP4 to MKV
If the video and audio are already in standard formats (H.264 video with AAC or AC3 audio), moving from MP4 to MKV is often a “remux,” not a re-encode.
Translation: the box changes, the actual streams stay bit‑for‑bit the same. No quality loss, and it is fast.
MKV to MP4
This is where things break.
MP4 does not support everything MKV can store. When I moved some packed MKV files into MP4, a few things dropped:
• Some subtitle formats did not make it unless I converted them first.
• Extra audio tracks were fine, but weird codecs needed conversion.
• Fancy chapter data sometimes vanished.
If your MKV is simple, MKV to MP4 is painless. If it is loaded with extra tracks, you should expect to lose some features or to spend time converting them.
Tools I actually used
HandBrake
Good when you want to re-encode or change resolution/bitrate.
I used it when I wanted to shrink huge MKV files into something more stream‑friendly MP4. GUI is clear enough once you mess with it for a bit.
FFmpeg
This is the blunt instrument. Command line only, but once you learn a few commands, it is fast and predictable.
For example, if the codecs are already supported, I used something like:
ffmpeg -i input.mkv -c copy output.mp4
That tells FFmpeg to move the streams as is into a new MP4 container. No quality change, no long encode.
If the MP4 target does not support a track, you need to pick a different codec instead of “copy” for that track. That is where you fall into guide-reading territory.
Video players that did not annoy me
Here is where I stopped experimenting and stuck with a few that behaved.
Elmedia Player on Mac
On my Mac, Elmedia handled every MP4 and MKV I threw at it. It switched audio tracks smoothly, picked up subtitle files without effort, and did not choke on large MKVs. Interface feels simple enough that I did not get lost in settings panels.
VLC Media Player
VLC is the cockroach of media players, in the good sense. It runs on almost anything and plays formats that other apps pretend do not exist.
I use it when nothing else works, or when I am on some random machine. It reads both MP4 and MKV with all the usual extras.
MPV
MPV is lighter and more barebones. On my setup it used less resources than VLC with high bitrate MKVs.
You get fewer menus and more config files. If you like to tune playback behavior, MPV is nice. If you want a click-and-forget app, it feels rough.
PotPlayer on Windows
On Windows, PotPlayer gave me smooth playback on heavy MKV files that stuttered in some default players. Subtitle handling was sharp, audio track switching was instant. It exposes a lot of knobs, so I had to turn off a bunch of stuff I did not need, but after that it stayed out of the way.
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For what you want, think in terms of “library strategy” more than “which is best.”
MP4 vs MKV for your use
Your goals:
• Good quality
• Small file sizes
• Wide compatibility with phones, TVs, sticks
For that combo, MP4 as your default target makes life easier.
MP4
Pros:
• Works on iOS, Android, smart TVs, Apple TV, Fire TV, game consoles, etc.
• Most streaming apps and DLNA servers expect it.
• Safer choice if you share with family who use random devices.
Cons:
• Limited extras. Advanced subtitles, weird audio codecs, multiple versions in one file often cause trouble.
• Some devices refuse high bitrate or odd frame rates even inside MP4.
MKV
Pros:
• Great for your “master” copies of movies and shows.
• Handles many audio tracks, commentary, lossless audio, lots of subtitle formats, chapters.
• Nice if you care about keeping original quality and options.
Cons:
• Older TVs and cheap sticks sometimes fail on MKV or drop subtitles or extra tracks.
• Some mobile apps ignore chapters or soft subs in MKV.
• Casting from phone to TV with MKV is hit or miss.
Where I slightly disagree with @mikeappsreviewer is on how universal MKV support feels. Newer devices still surprise you with half baked MKV handling. Subtitle support is often the weak link, not the container itself.
Practical setup that works well
If you want simple, do this:
-
Keep an “archive” version in MKV
• For movies you care about, store a high quality MKV with full audio tracks and subtitles.
• Good for local playback on a PC or Mac with VLC or Elmedia Player.
• Elmedia Player handles MKV, multiple audio tracks, and subs cleanly on Mac and is less clunky than some others. -
Create “play everywhere” copies in MP4
• Encode H.264 video and AAC or AC3 audio.
• Use one main audio track and common subtitle formats like SRT.
• These MP4 files will work on almost all phones and TVs.
Think of MKV as your shelf copy. Think of MP4 as your “works on every screen in the house” copy.
File size vs quality
Container choice does not control size or quality. The codec and bitrate do.
For your library:
• H.264 video, 1080p, around 4 to 8 Mbps is usually fine for movies and TV.
• AAC stereo at 160 to 256 kbps or AC3 5.1 at 384 to 640 kbps.
• Same settings give similar size, whether in MP4 or MKV.
So if you see big MKV vs smaller MP4, it is because of different bitrate or codecs, not because MKV is huge and MP4 is small.
Device behavior examples
From testing in my setup:
• Older Samsung and LG TVs: MP4 works more often. MKV sometimes loses subs or certain audio.
• Fire TV and newer Chromecast: MKV works, but casting from phone apps with MKV is less reliable.
• Phones: MP4 wins for stock players. MKV needs third party apps more often.
So, for a mixed family library, MP4 as default playback format saves you support headaches.
Simple rules to use
- For anything you want to play on phones, TVs, and sticks with minimal fuss, use MP4 with H.264 + AAC/AC3.
- For long term storage of full quality rips with multiple tracks, use MKV.
- Do not convert MKV to MP4 unless you need it for a specific device. Expect some subtitles or weird audio formats to need conversion.
- Use a solid player on your main computer. Elmedia Player on Mac is fast, handles MP4 and MKV, and deals well with subs and audio tracks.
If you describe one problem file, like codec details and what device fails to play it, people here can point to specific settings.
Short version: use both, for different jobs.
If you want one rule to reorganize your library:
- MKV for your “masters”
- MP4 for “plays everywhere without drama”
@ mikeappsreviewer and @ waldgeist already nailed most of the container stuff, so I’ll just tilt it a bit toward what you actually care about: quality, size, and things not randomly failing on your TV on movie night.
1. Quality & file size
Container (MP4 vs MKV) barely matters here. What matters is:
- Video codec: H.264 or H.265
- Bitrate / CRF setting
- Audio codec: AAC / AC3 / etc.
Same encode settings in MP4 vs MKV will be almost identical in size and quality. If your MKVs are larger, it is usually because:
- Higher bitrate
- More audio tracks
- More subtitle tracks
- Lossless or higher quality audio
So don’t switch to MP4 expecting smaller files by magic. If you want smaller, you have to re-encode with lower bitrate or H.265.
2. Compatibility (your main concern)
For phones, TVs, and streaming boxes right now:
-
Most compatible setup:
MP4 + H.264 video + AAC or AC3 audio + simple subtitles (SRT).
This is what almost every device vendor tests against. -
“Good but sometimes flaky” setup:
MKV + any random combo of codecs, subtitles, chapters, multiple audio tracks.
Newer gear often handles it fine, but you will find that one stubborn TV that drops subs or refuses playback.
Where I slightly disagree with @ waldgeist: MKV support on “modern” TVs is still hit or miss, especially with subtitles and weird audio. It is not just an “old TV” problem. Vendors love half baked MKV support.
3. How I’d organize your library
If I were in your situation, trying to tidy things up:
-
Keep / convert to MKV for:
- Full quality movie backups
- Multiple language tracks
- Director’s commentary
- Multiple subtitle tracks
- Stuff you mainly watch on a computer or a proper media player
-
Keep / convert to MP4 for:
- Things you cast from phone to TV
- Stuff you sync to iPhone / iPad / Android
- Family‑friendly “no one calls me to fix the TV” versions
- Any file you might copy to USB and plug into a random TV or car system
Think of MKV as the Blu‑ray case and MP4 as the travel sized version.
4. Playback apps
On a PC/Mac, you can basically ignore the container war:
- Use VLC, MPV, etc. for “plays almost anything.”
- If you are on macOS specifically, Elmedia Player is actually really solid for both MP4 and MKV. Handles multiple audio tracks and subtitles nicely and is less clunky than VLC for everyday use.
If you install something like Elmedia Player on your Mac, you can happily keep your MKV “masters” and only bother making MP4 copies for devices that complain.
5. What I’d actually do, step by step
Not going into tool commands since @ mikeappsreviewer covered that, but strategy wise:
- Decide which files are “archive” and which are “everyday watching.”
- Archive ones: keep or convert to MKV, keep all tracks.
- Everyday ones: convert to MP4, keep:
- H.264 video
- Single main audio track (maybe a second if you really care)
- SRT subtitles only
You end up with:
- MKV folder: big, complete, future proof.
- MP4 folder: lean, simple, plays on phones, TVs, sticks with minimal headaches.
So “which is better” for you?
- For playability across phones/TVs/streamers: MP4 wins.
- For feature rich backups and flexibility: MKV wins.
Use each where it shines instead of trying to crown one universal champion.