Why your iPhone video won't play on your PC, and how a browser tab fixes it in seconds

You AirDrop a video from your iPhone to your laptop, double-click it, and get an error. Or sound with no picture. Or a player asking you to buy a codec. The video isn't broken: it's in a format many devices don't handle. The usual fix is an online converter, which means sending your file to someone else's server. It no longer has to work that way.

Container vs codec: why the video won't play

A video file has two layers. The container (.mov, .mp4, .mkv) is the box. The codecs inside it decide how the picture and sound are compressed. Since iOS 11 (2017, iPhone 7 and later), iPhones record MOV files with HEVC (H.265) video by default. HEVC is about half the size of H.264 at the same quality, but it is patent-encumbered, so support is patchy.

• Windows doesn't play HEVC out of the box. Microsoft sells HEVC Video Extensions for about $1, and there is also a free "HEVC Video Extensions from Device Manufacturer" package that doesn't show up in a normal Store search.
• Many Android phones, smart TVs, older laptops and video editors don't decode HEVC.
• Plenty of upload forms and course platforms only accept MP4.

Change the box, re-encode only when needed

MOV to MP4 is often not a conversion at all. If the streams inside are H.264 or HEVC with AAC sound, they can be moved into an MP4 unchanged: no quality loss, and a 400 MB clip is done in seconds. When the device simply can't decode HEVC, the video has to be re-encoded to H.264, which every computer, phone, TV and browser plays.

That used to need a server. Today browsers ship WebCodecs, which gives a web page direct access to the device's own, usually hardware-accelerated, video encoders and decoders. 4Dev uses it together with the Mediabunny library, which reads and writes the containers:

const input = new Input({ source: new BlobSource(file), formats: ALL_FORMATS });
const output = new Output({ format: new Mp4OutputFormat(), target: new BufferTarget() });
const conversion = await Conversion.init({ input, output });
await conversion.execute();

• Keep original quality: the streams go into the MP4 unchanged. Fastest, and enough when the problem is the .mov extension.
• High, Medium or Low quality: the video is re-encoded and HEVC becomes H.264. This is the fix for a PC that shows sound with no picture.
• Trim or set a target size in MB to make it fit email or a chat app.

IMG_0412.MOV  HEVC · 4K · 380 MB  →  IMG_0412.mp4  H.264 · 1080p · ~60 MB

Which settings to choose

The right choice depends on where the video is going. A few rules of thumb:

• Sharing in a chat or by email: 1080p or 720p, or a target size. Many email services cap attachments at about 25 MB.
• Uploading to a website or a form: H.264 in MP4 at 1080p is accepted almost everywhere.
• Editing on a Windows PC: keep the original resolution and pick the highest quality, so you don’t lose detail before the edit.
• Archiving: keep the original MOV file as well. Every re-encode loses a little quality, so convert copies, not your only file.

Tip: the iPhone setting

Settings → Camera → Formats → “Most Compatible” makes the iPhone record H.264 instead of HEVC. The files are bigger, so many people keep HEVC and convert only the videos they share.

Why renaming the file doesn’t help

Changing IMG_0412.MOV to IMG_0412.mp4 only changes the label on the box. If the video inside is HEVC, a device that can’t decode HEVC still can’t play it. Sometimes a renamed H.264 file does play, but it is not a proper MP4, and strict upload forms can still reject it. Converting rewrites the container correctly and, when needed, the video itself.

Limits worth knowing

Files can be up to 2 GB. It works in current Chrome, Edge, Safari and Firefox on a computer and in Chrome or Safari on a phone, and the format list only offers what your browser can actually create. Long 4K clips take a while, so for a quick share pick 1080p or a target size.

Photos and documents too

iPhone photos have the same problem: they are saved as HEIC, which is also based on HEVC, and the HEIC to JPG converter fixes them the same way, up to 50 at once. PDF to Word also runs on your device, so contracts and CVs never leave it either. HEIC conversion works only in Safari.

The takeaway

• If a video won't play, the codec is usually the problem, not the file. Renaming .mov to .mp4 doesn't change what's inside.
• Changing the container is instant and lossless; re-encode to H.264 only when a device can't play HEVC.
• Your browser can now do this on your own device, so private files don't need to be uploaded anywhere.

Open the MOV to MP4 converter