MP4 / MOV
The formats your iPhone does open — which makes it stranger when one of them will not.
MP4 and MOV are the containers Apple built its systems around, so a file that fails is almost never failing because of the wrapper. Something inside it — a 10-bit H.264 stream, DTS or TrueHD audio, AV1 on an older chip — is a codec the device cannot decode, and the container gets the blame.
30 July 2026
Opened without help by
Native support is for the container and for the codecs Apple ships decoders for. Both are needed. A perfectly valid MP4 holding a stream the hardware has never heard of opens, shows a black frame or plays silently, and gives no useful reason.
The facts
| Full name | MPEG-4 Part 14, and QuickTime File Format |
|---|---|
| Kind | Containers — the same design, two names |
| Extensions | .mp4, .m4v, .mov, .m4a (audio only) |
| Published | MOV in 1991 by Apple; MP4 in 2001, derived from it |
| Video that always works | H.264 up to High profile, 8-bit; HEVC on any device from 2015 on |
| Video that often does not | H.264 High 10 (10-bit), MPEG-4 Part 2 (DivX/XviD), AV1 on hardware before 2023 |
| Audio that always works | AAC, ALAC, MP3, PCM |
| Audio that often does not | DTS, DTS-HD, TrueHD, Vorbis, Opus in an MP4 |
| Subtitles | Closed captions and one timed-text format; nothing like the range an MKV holds |
One format wearing two names
MOV came first: Apple published QuickTime in 1991, and its file layout was good enough that when the MPEG group needed a container for MPEG-4, they took it and standardised it. That is why MP4 and MOV are structurally almost the same thing — boxes of metadata describing tracks of media — and why a tool can usually rename one to the other and have it still work.
The practical difference is what each is *allowed* to hold. MOV, being Apple's own, accepts anything QuickTime ever supported, including ProRes and codecs no phone will ever decode. MP4 is the stricter, more portable standard. Neither of them was designed to carry eight subtitle languages and a dubbed audio track, which is the gap Matroska filled.
Because these are the formats every Apple device opens, they are also the destination of nearly every conversion. "Convert to MP4" is shorthand for "put this into the box iOS will accept".
Then why does this one not play?
Because opening a file takes two things, and only the first is about the container. The system reads the box, finds the tracks, and then asks its decoders to turn those tracks into picture and sound. If a decoder is missing, everything up to that point still succeeded — which is why the failure looks so odd. The file opens. There is a duration. There is a scrub bar. There is nothing to watch.
The symptom tells you which half broke:
- Sound but no picture — the video codec is unsupported. On Apple hardware the usual culprit is 10-bit H.264, often written *Hi10P*, which is common in anime releases. Hardware H.264 decoders are 8-bit only, and there is no software fallback in the system player.
- Picture but no sound — the audio codec is unsupported. DTS and TrueHD are the ones you meet on anything ripped from a disc.
- Neither, and an error — usually a broken or truncated file, or an MP4 whose index sits at the end and never arrived.
- Both, but it stutters — nothing is unsupported; the bitrate or resolution is simply more than that chip wants to do.
A player carrying its own decoders sidesteps all of this, because it never asks the system. It decodes 10-bit H.264 and DTS itself, in software, and hands finished frames to the screen.
What to do about it
- Find out what is actually inside
Before converting anything, look at the file's streams. If the video is 10-bit H.264 and the audio is DTS, you know precisely what needs to change — and often that only the audio does, which is a two-second job rather than an hour.
- Re-encode only the stream that fails
Converting an entire file because its audio track is DTS wastes an hour and loses picture quality for nothing. Replacing just the audio track keeps the video bit-for-bit identical.
- Play it with something that decodes in software
Nothing to convert and nothing to work out: a player with its own decoding stack opens 10-bit H.264, DTS and TrueHD directly. This is what FoxDL does — the same reason it opens MKV also covers the MP4 that Apple's player will not.
Two things that look like format problems and are not
A desktop CPU brute-forces what a phone expects its hardware decoder to do. Nothing about the file is wrong; the same file at a lower bitrate would be fine.
An MP4 keeps an index of where everything is. When it is written at the end of the file, a player must have the whole file before it can jump anywhere. Moving that index to the front — sometimes called *faststart* — is a rewrite of a few kilobytes, not a conversion.
Questions about this format
Nearby formats
Your library, finally in one place.
Free to download. No account, no sign-up, nothing to hand over.