Question 1

Does converting MOV to MP4 lose quality?

Accepted Answer

Not if the file is one of the ordinary ones, and most are. A MOV off an iPhone, a camera or a screen recording holds H.264 or H.265 video with AAC sound, and those are exactly what an MP4 holds too. So the picture and the sound are lifted out of one container and put into the other with nothing decoded on the way, which leaves you the same video, bit for bit, in a different box. It finishes in about the time it takes to read the file off your disk. The exceptions are real, and this page names them on the file's own row before it starts: a WebM full of VP9, an old recording with uncompressed sound, or you asking for H.264 when the file holds H.265. Those genuinely have to be re-encoded, and that does cost a little.

Question 2

Can I just rename a .MOV file to .MP4?

Accepted Answer

Sometimes, and it is worth knowing when. Both sit on the same underlying file format, so if the MOV holds H.264 video and AAC audio, changing the extension often works and the file plays. Where it stops working is everywhere else. A MOV holding ProRes, uncompressed PCM sound or a QuickTime timecode track is still a QuickTime file with a new name on it, and the player that opens it will either refuse it or play the picture without the sound. Renaming also leaves the branding inside the file saying QuickTime, which some upload forms check. Dropping it here reads what is actually inside and writes a real MP4 around it, which takes seconds and works in every case rather than most of them.

Question 3

How do I convert MKV to MP4?

Accepted Answer

Drop the MKV in. MP4 is already selected, and most MKVs come out with nothing re-encoded, because the H.264 or H.265 inside one is what an MP4 wants as well. What usually needs saying about an MKV is the rest of it: a film in an MKV often carries two or three audio tracks and a set of subtitles, and all of them are listed on the file's row before anything happens. Every audio track comes across by default, and each one has a tick you can clear. The same selector works in the other direction, so for MP4 to MOV or MP4 to MKV you pick MOV or MKV under Container and drop the file in as normal.

Question 4

How do I convert WebM to MP4?

Accepted Answer

Drop it in, and expect this one to take longer than the others. A WebM holds VP9 or VP8 video, which an MP4 can technically carry and virtually no phone, television or editor will play out of one. So this is the case where the honest answer is to re-encode the picture as H.264, and the row says so before it starts rather than after. How long it takes depends on the length and the resolution: a short screen capture is quick, a full-length 4K clip is minutes. If what you have is a browser recording you only want the sound out of, that is a different and much faster job.

Question 5

Will the subtitles survive in the MP4?

Accepted Answer

Text subtitles do. An MKV's subtitle tracks are read out of the file, listed on its row, written into the MP4 as a real subtitle track, and saved as .srt files alongside the video, so you have them whichever way the thing you are sending them to expects. SRT, ASS and WebVTT tracks all read. Picture-based subtitles are the exception and they are named rather than dropped quietly: PGS and VobSub tracks, which is what most Blu-ray rips carry, are images of text rather than text, so there is nothing to turn them into without reading the pictures back. MKVToolNix pulls those out of a file, and VLC displays them from the original.

Question 6

What happens to the second audio track or the commentary?

Accepted Answer

It comes across. Every audio track in the file is carried into the new one and listed on the row with its codec, its channel count and its language, so a film with a German dub and an English original arrives with both. That matters more than it sounds. A converted film that quietly lost its second language is a broken file, and you find out in front of the television rather than at the computer. If you want a track gone, open the settings on that file's row and untick it. Turning the sound off entirely is one switch under the tool, which is the answer to wanting a video with no audio at all.

Question 7

Is there a limit on file size or length?

Accepted Answer

No. Nothing caps how large a file is, how long it runs, or how many are in the list, and there is no allowance to use up. The file is read in slices off your disk rather than loaded whole, so a 5 GB recording never has to fit in memory at once. What a big file costs is reading time rather than processing time: a copy runs at the speed your disk delivers, so a ten-minute 4K clip is seconds. Re-encoding is the slow path, and it is also the one you rarely need. Which of the two a given file is about to take is on its own row before you start it.

Question 8

Why won't my iPhone video play on Windows?

Accepted Answer

Because of what is inside it, not the extension. Recent iPhones record H.265, also called HEVC, which macOS and iOS play natively and Windows does not unless someone installed the codec from the Microsoft Store. Renaming the file changes nothing, and converting it to MP4 on its own changes nothing either, because the H.265 comes across untouched. What fixes it is setting Picture to Convert to H.264 before you convert. That re-encodes the video, so it takes minutes rather than seconds and it is the one setting here that costs a little quality, but the file plays everywhere afterwards. To stop it happening again, set Camera, Formats to Most Compatible on the phone.

Question 9

Can I convert a whole folder of episodes at once?

Accepted Answer

Yes. Press Choose a folder and pick the folder itself rather than the files inside it, which is what a season of a series is once it is sitting on your disk. Everything in it that holds video joins the list, and the artwork, .nfo files and stray text files stay where they are. Several convert at the same time, each with its own progress bar, and the settings under the tool apply to all of them unless you change one on its own row. When they are done you can take the lot as a single ZIP, subtitle files included. Two episodes with the same name from different folders each get a name of their own.

Question 10

Do my files get uploaded anywhere?

Accepted Answer

No, and there is no server here that could receive one. Your video is read and written back out by your own browser on your own machine. If you would rather check than take that on trust, open the network tab and convert something: nothing goes out. It matters more here than on most pages, because of what people put through a video converter. A wedding video, a client's footage, an interview, a recording of a child. Uploading is also the slowest part of any process that asks for it, since a 4 GB file has to finish going up before anything happens to it. Clear the list afterwards and nothing is left.

Question 11

Can I convert an AVI or a WMV file here?

Accepted Answer

No, and the reason is worth having rather than a shrug. Drop one in and its row tells you what it holds, which is usually Xvid, DivX or Motion JPEG for an AVI, and Windows Media Video for a WMV. No browser ships a decoder for any of those, so there is nothing here to read them with, and they cannot be copied into an MP4 either, because an MP4 has no place to put them. That is a limit of what a browser can do rather than a setting to go looking for. VLC opens both and can save one out as an MP4 or an MKV, and HandBrake converts them properly on Windows, macOS and Linux. A file saved out of either works here afterwards.

Question 12

How do I convert MOV to MP4 on a Mac?

Accepted Answer

For a single file, macOS does it without a browser at all. Open the MOV in QuickTime Player, then File, Export As, and pick 1080p or 4K: what comes out is an .mp4. iMovie exports one too, and HandBrake is the free download people usually mean when a file is stubborn. Come back here when you have a folder rather than a file, when you want the video copied across untouched instead of re-encoded, which the QuickTime export does not offer, or when the file has more than one audio track to keep. Windows has no built-in equivalent at all, which is why the question comes up far more often there.

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