XPRTIX Video

Add faststart to an MP4.

Move the moov atom to the front so an MP4 starts playing before it finishes downloading. No re-encode, and the file stays on your device.

moov → fronthev1 → hvc1ProRes → H.264AC-3 → AAC
Drop your videos here or click to browse MP4MOVM4V Up to 50 MB when a re-encode is needed

XPRTIX Video

Add faststart to an MP4: how it works

What faststart does

An MP4 keeps its map of the video (track layout, codecs, where each frame sits) in a block called the moov atom. Many tools write it at the end of the file. A player then has to download the whole video before it can start, which on iPhone, Safari and the web feels like a video that is slow to start or will not play. Faststart moves moov to the front.

How to use it

Drop the MP4 or MOV on the page. If the moov atom is at the end, the report says so and gives you a corrected file. Only the box order changes; the video and audio are copied byte for byte, so there is no quality loss and it is quick, even for large files.

Where it matters

Any video you put on a website or send as a link benefits, as playback can begin right away. It is also one of the common reasons a video fails on iPhone.

Why it fails

Why videos don't play on iPhone

A video can be perfectly valid and still refuse to play on iOS. These are the four usual causes. XPRTIX Video repairs all of them.

  1. 01

    The moov atom is at the end

    An MP4 keeps its metadata (track layout, codecs, sample offsets) in a box called moov. Written after the media data, a player must download the entire file before it can start. Moving it to the front is faststart.

    Fixed in your browser
  2. 02

    HEVC tagged hev1, not hvc1

    Both tags describe identical HEVC video; only the label differs. Apple plays hvc1 inline and refuses hev1. The video itself is unchanged, so this is a tag rewrite and quality is untouched.

    Fixed in your browser
  3. 03

    A codec iOS won't decode

    MPEG-4 Part 2, ProRes and VP9 need converting to H.264, as do the H.264 High 4:2:2 and 4:4:4 profiles: valid H.264 that iOS still refuses to play.

    Re-encoded on the server
  4. 04

    Audio that plays as silence

    AC-3, E-AC-3 and PCM tracks leave you with a video that plays with no sound at all on iOS. They are converted to AAC.

    Re-encoded on the server

Transparency

What leaves your device

Said up front, before anything is dropped.

Stays on your device

  • Checking every video. Only the atom headers and the moov box are read: a few kilobytes, whatever the file size.
  • Faststart and hev1 → hvc1 repairs. They are container rewrites, so the video is never uploaded.

Sent to the server

  • Only a video that needs re-encoding: an unsupported codec, profile or audio track.
  • The upload is deleted as soon as the encode ends, and the result shortly after you save it.

Recorded

  • Anonymous usage data: the file name, size and format details, what was done and whether it worked.
  • Never the video itself. No account, no tracking across sites.

Video guides

Common Video jobs

Questions

Asked often

Is faststart the same as -movflags +faststart in ffmpeg?

Yes, the result is the same. This does it in your browser without a command line.

Does it re-encode the video?

No. The streams are copied unchanged.

Is there a file size limit?

Faststart runs in your browser, so there is no practical limit.

How do I know if my MP4 needs faststart?

Drop it here. The report says whether the moov atom is at the end of the file.

Does faststart make the file smaller?

No. The file is the same size; only the order of its parts changes.

Why does my video take long to start on a website?

When the moov atom is at the end, the browser has to fetch the whole file before it can play. Faststart fixes that.