How to convert a video so WhatsApp will send and play it

WhatsApp wants MP4 with H.264 video and AAC audio. That is the combination that arrives as a playable thumbnail in the chat for every recipient, on both iPhone and Android, with no extra app involved.

If your file is a MOV from an iPhone or an MKV that already holds H.264, getting there is a container swap rather than a re-encode. It finishes in seconds and the picture is bit-for-bit identical. You can do it in the converter on this site, which runs entirely in your browser tab.

The format WhatsApp actually wants

WhatsApp has to play your video on hundreds of different handsets, many of them cheap Android phones several years old, and it has to do it inside its own player rather than handing the file to the operating system. So it targets the lowest common denominator that every phone shipped with a hardware decoder for: H.264 video and AAC audio, wrapped in an MP4 container.

Three separate things have to be right, and people routinely fix only one of them:

• The container — the .mp4 wrapper that says where each frame starts. MOV, MKV, AVI, WMV and TS are different wrappers.
• The video codec — H.264 is universally safe. HEVC (H.265) is what a modern iPhone records by default, and whether it plays for the person receiving it depends entirely on their device. VP9 and AV1 are web codecs and have no business in a chat attachment.
• The audio codec — AAC. AC-3 and DTS are common inside MKV files ripped from discs, and a phone player will usually show the picture and stay silent. If that is your symptom, the longer explanation is in the guide on a video that plays but has no sound.

Get all three right and the file goes through as media. Get one wrong and you hit one of the failures below.

Why your video will not send, or arrives as a file nobody can open

There are only a few distinct failures here, and the fix is different for each.

The attachment picker will not show the file

If you tap the camera-roll or gallery icon and your MKV or AVI simply is not listed, that is not WhatsApp being awkward — the phone's own media library never indexed it. iOS and Android photo libraries hold MOV and MP4. An MKV that you copied across from a laptop lives in the Files or Downloads area instead, outside the gallery, so the media picker cannot see it.

It sends, but as a document

Attach that same MKV through the Document option and it will go — untouched, at full size, with no compression. But it lands in the chat as a grey file row rather than a video thumbnail. The recipient has to download it and find a player that opens MKV, which on a stock iPhone means installing one. Technically delivered; practically useless.

It sends as media, but the recipient sees a black screen or a spinning loader

This is usually a codec the receiving handset cannot decode, and HEVC is the common culprit. It is the same mismatch that makes an iPhone video refuse to play on an Android phone when you send it by any other route. Converting the video to H.264 removes the guesswork.

Converting it, step by step

1. Open the converter. It runs an FFmpeg build compiled to WebAssembly inside your tab — your file is never uploaded, because there is no server to upload it to.
2. Drop the video in. Read the codec line it shows you.
3. Choose MP4 as the output.
4. Look at what the tool says it is about to do. It states in words whether it will copy the streams or re-encode them.
5. Press Convert, then save the result and send it from your phone or from WhatsApp Web.

If it says copy, the job takes seconds no matter how long the clip is, and nothing is recompressed. If it says re-encode, expect it to be slow: the browser build is single-threaded, so a 720p re-encode runs at roughly the speed of the footage itself and 1080p is slower than that. A five-minute 1080p clip is a coffee, not a click.

Which files swap containers and which have to be re-encoded

A stream copy is genuinely lossless. A re-encode is not, at any quality setting — you are decoding the picture and drawing it again. If you are starting from an MOV or an MKV and want to understand where the line falls, there are dedicated guides on converting MOV to MP4 without losing quality and on doing the same with MKV.

Size, and WhatsApp's own compression

WhatsApp enforces a size ceiling on attachments, and the number has moved more than once — check it in WhatsApp's own Help Centre rather than trusting any article, this one included, that quotes a figure. What matters more is the behaviour behind it, and that has been stable for years:

• Anything sent as media gets recompressed by WhatsApp. It will re-encode and often downscale your clip before it leaves your phone, so an immaculate 4K master is largely wasted effort — the recipient sees WhatsApp's version of it, not yours.
• Anything sent as a document is passed through untouched, which is the trick people use for a wedding video that has to survive intact. The price is the grey file row instead of an inline thumbnail.

Because your clip is going to be squeezed anyway, there is little point uploading a huge file. If yours is over the limit and you cannot cut it down, the same problem and the same workarounds show up in the guide on video files that are too large to email.

Settings worth changing, and ones that are not

For a clip destined for a chat window, the defaults are close to right. Two advanced options are worth a look:

• Resolution. Dropping to 720p before you send costs you very little on a phone screen and makes the re-encode considerably faster. The converter never upscales, so setting 1080p on a 720p source does nothing.
• Frame rate. If your source is 60 fps and the content is people talking rather than sport, 30 fps roughly halves the work.

Leave the quality preset alone unless you have a reason. The default is constant-quality encoding, so the file only grows as large as the footage needs. And ignore the 3GP output entirely — it exists for genuinely ancient phones and caps the width at 640 pixels; WhatsApp has no use for it. If you are specifically stepping down from HEVC, the HEVC to H.264 converter is set up for exactly that job.

Converting on the phone, without the browser round trip

The awkward part of all this is that the video is usually already on your phone, and a browser converter means moving it to a computer and back. Our Video Converter app does the same job on the device: import from the camera roll or Files, convert between MP4, MOV, AVI, MKV and 3GP at Low, Medium or High quality, then send it straight out through the system share sheet into WhatsApp. It keeps a history of what you have converted.

It uses the phone's own hardware encoder, which is why it is far quicker than any browser on long or 4K footage, and it has no file-size ceiling. The trade-off is that it always re-encodes — there is no stream-copy mode, so a MOV that the browser tool would have remuxed losslessly in seconds gets encoded again here. On iPhone the first conversion is free and further conversions need the paid upgrade; on Android it is free and unlimited.

Which one to reach for: if the clip is on your phone and you just want it sent, use the app. If the file is already H.264 and you would rather not encode it again, use the browser converter and let it copy the streams.