Convert WEBM to MP4 on iPhone Without an App

You have a.webm file sitting in Files, or in a chat, and your iPhone is being useless about it. Tap it and you get a grey screen or a spinning wheel. Try to save it to Photos and the option is not there. Try to attach it somewhere and the recipient cannot open it either.

Nothing is broken. WEBM is simply a format Apple never adopted, and the iPhone is behaving exactly as designed. I built a free Shortcut that deals with the aftermath of this kind of thing, so let me explain what is actually happening and then give you the shortest route out.

What a WEBM file is

WEBM is a container format Google created for the open web. It usually holds video encoded with VP8 or VP9 and audio encoded with Vorbis or Opus. It is free of licensing fees, which is why so much of the web uses it, and it is very good at what it does.

MP4 is the container Apple standardised on, normally holding H.264 or HEVC video with AAC audio. Every Apple device decodes those in hardware, which is why an MP4 plays instantly and uses barely any battery.

The gap between those two lists is the whole problem. It is a codec and container question rather than anything to do with quality. A WEBM is not a worse file, it is a file your phone was never taught to handle in its own apps.

Where iOS does and does not cope

This is the part that confuses people, because WEBM does work in one place on your iPhone.

• Safari plays a lot of WEBM video embedded in web pages on current iOS versions. That is why a video plays fine in the browser and then refuses to open once you have saved it.
• The Photos app will not accept a WEBM at all. There is no import path. Photos handles Apple’s formats and that is the end of it.
• Files can store one and cannot preview it. You can keep the file, move it, rename it, and share it. Tapping it gets you nothing useful.
• Most apps you would send it to will reject it. Messages, WhatsApp and Mail will attach it as a generic file rather than a playable video.

exactly which codec profiles inside WEBM the current Safari release decodes, since VP9 and AV1 support has shifted across iOS versions.

Renaming the file does absolutely nothing

Getting this out of the way early, because it is the top suggestion on forums and it is wrong. Changing clip.webm to clip.mp4 in the Files app does not convert anything.

The extension is a label on the outside of the box. The bytes inside are still a Matroska style container with VP9 video in it, and Photos will either refuse the file or accept it and then fail to play it.

Real conversion means decoding the video and re-encoding it as H.264 or HEVC inside an MP4 wrapper. That is computation, and it has to happen somewhere.

iOS has no built in converter for this

Here is the honest structural fact. Apple’s Shortcuts app has actions that encode media, and they target Apple’s own formats from sources iOS already understands. There is no VP9 decoder exposed to Shortcuts, no ffmpeg on your phone, and no hidden conversion option in Files.

So any guide claiming a fully on-device, no-website WEBM to MP4 conversion on a stock iPhone is describing something that does not exist. Every real route sends the file somewhere that can decode VP9. The only question is how much friction is involved in getting it there.

The route I actually use

Grabio is a free Apple Shortcut. It sits in your share sheet, and for jobs iOS genuinely cannot do it opens a good third party converter with the job already set up rather than pretending it did the work itself.

1. Open the WEBM in Files. If it is in a chat app, save it to Files first.
2. Tap the Share button.
3. Scroll the share sheet and tap Grabio.
4. Choose the video conversion option and pick MP4.
5. Grabio opens VERT in Safari. VERT is free and open source, and it does not bury the page in ads.
6. Tap the upload area, pick your WEBM from the file picker, choose MP4 as the output, and download the result.
7. Once the MP4 is on your phone, share it to Photos so it lives in your camera roll like any other video.

The manual file picking step is unavoidable. iOS forbids any app, mine included, from placing a file into a website’s upload field on your behalf. It is a system security boundary that applies to every app on the phone. Anyone advertising a fully automatic file-to-website flow on iPhone is describing something the operating system does not allow.

Be clear about the trade you are making. On this route the file goes to a third party server to be converted, and that service’s own privacy policy is the document that governs what happens to it there. If the video is sensitive, that is a real consideration and I would rather say it plainly than skip past it.

Grabio is free, there is no account and there is no App Store install. Get the Shortcut if you hit awkward file formats often.

Fixing it at the source, which is usually better

If you are getting WEBM files repeatedly, look upstream. Wherever the file is coming from can often give you an MP4 directly, and one conversion avoided beats one conversion done well.

Screen recorders and web based export tools frequently default to WEBM with an MP4 option one setting away. Discord and similar apps preserve whatever format was uploaded, so ask the sender to export differently. And if the source is a web page, the video may well be available in MP4 form from the same site.

The general map of what converts natively on an iPhone and what needs help is in converting any file format on iPhone. It is worth a read if this is a recurring annoyance rather than a one off.

After the conversion

Two things usually follow. The MP4 you get back may be larger than the WEBM was, because VP9 compresses more aggressively than H.264 at the same visual quality.

If that pushes you past an upload limit, compress it: the sizes different services accept are laid out in shrinking a video for WhatsApp and other apps, and for genuinely large files sending a large video from an iPhone covers the routes that do not involve compressing at all.

The other common follow up is that you only wanted the audio. If so, skip the video conversion entirely and go straight to extracting audio from a video on iPhone, which saves you a step and a lot of file size.

What about WEBM images?

Worth knowing, since the extension is used for both. Some WEBM files are short silent animations acting as an animated image, the way a GIF does.

Those convert the same way, and if what you actually want is a GIF rather than an MP4, choose GIF as the output format instead. The trade offs between the two, including why GIFs are enormous for what they are, are in converting a video to a GIF on iPhone.

WEBM to MP4 on iPhone: FAQ

Why will my iPhone not play a WEBM file?

Apple never adopted the format. WEBM normally contains VP8 or VP9 video, which the Photos app and the Files preview do not decode. Safari handles a lot of WEBM on web pages, which is why the same video plays in the browser and fails once saved.

Can I convert WEBM to MP4 on iPhone without an app?

Yes, without an App Store app. There is no on-device converter in iOS, so the file has to reach something that can decode VP9. A free Shortcut can hand it to a free web converter and bring the MP4 back.

Does renaming.webm to.mp4 work?

No. The extension is only a label and the contents are unchanged, so Photos will still refuse the file or fail to play it. The video has to be decoded and re-encoded to become a real MP4.

Will the converted MP4 look worse?

There is a small quality loss because the video is re-encoded. It is rarely visible at sensible settings. The larger surprise is that the MP4 is often bigger than the WEBM, since VP9 compresses more efficiently than H.264.

Why do I have to select the file myself on the converter site?

iOS does not permit any app to place a file into a website’s upload field. It is a system level rule that applies to every app on your iPhone, so that extra tap exists no matter which tool you use.

Can I save a WEBM to my camera roll?

No. The Photos app has no import path for the format. Convert it to MP4 first, then share the MP4 to Photos and it behaves like any other video.