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The safest format for WhatsApp is MP4 with H.264 video and AAC audio. MOV files from iPhones usually work because they use the same codecs inside. MKV, WebM and AVI are hit and miss: WhatsApp may refuse them, send them as documents, or fail to play them on the recipient’s phone.
A video file has two separate layers. The container is the wrapper — MP4, MOV, MKV, WebM, AVI — and it determines the file extension. The codec is how the video and audio inside are actually encoded — H.264, H.265/HEVC, VP9, AV1 for video; AAC, MP3, Opus for audio.
WhatsApp cares about both. It handles the MP4 container well and understands H.264 and AAC on every platform. Put an unusual codec inside a familiar container, or a familiar codec inside an unusual container, and things start to go wrong in ways that look random but are not.
How the common ones behave in practice.
When WhatsApp does not recognise a file as playable video, it falls back to sending it as a generic document. It arrives as a file card, not an inline video, and whether it plays depends entirely on what the recipient has installed. On a stock Android phone, an MKV or WebM document often opens to an error.
This is the failure that generates the most confused messages: "I sent you a video" — "I got a file that will not open." The fix is always to get the video into an MP4 container with H.264 and AAC before sending.
Recent iPhones record in HEVC (H.265) by default because it is far more efficient than H.264. Between two modern phones this is fine. Sent to an older Android device, an HEVC video may show a black screen or refuse to play — the recipient’s hardware has no decoder for it.
If you regularly send to Android users and see this problem, switch the iPhone camera to a compatible format: Settings, Camera, Formats, then "Most Compatible". New recordings are H.264 from then on, at the cost of larger files.
A stream-copy splitter does not re-encode, which means it does not change the codec either. An MP4 with H.264 inside comes out as MP4 parts with H.264 inside — the format compatibility of the source is preserved exactly. WebM and MKV sources are split into WebM and MKV parts, since those codecs cannot be placed into an MP4 container without re-encoding.
The practical advice: if your source is MP4 or an iPhone MOV, split it and send. If your source is WebM, MKV or AVI, convert it to MP4 first — then split if it is still too long or too large.
Split a video into WhatsApp-ready parts
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Open the toolMP4 with H.264 video and AAC audio works everywhere. MOV from iPhones usually works too. MKV, WebM and AVI are unreliable and often get sent as documents rather than playable videos.
WhatsApp did not recognise the file as playable video, usually because of the container or codec. Converting to MP4 with H.264 and AAC makes it send as a normal inline video.
Newer iPhones record in HEVC (H.265), which older Android phones cannot decode. Set the iPhone camera to "Most Compatible" to record in H.264, or convert the video before sending.
Not when the splitter uses stream copy. The parts keep the same container and codecs as the source, so an MP4 comes out as MP4 parts with identical quality.
WhatsApp re-encodes videos sent as media to around 720p or below, so recording at 1080p is plenty. Higher resolution only increases the file size and the amount WhatsApp strips out.