Generated clips typically arrive in one specific, recognisable shape: H.264, sometimes HEVC, inside an MP4 container. MP4 is the box — a structure that can hold subtitles, multiple audio tracks and one of several possible video codecs inside it. H.264 or HEVC is what is actually doing the compressing. The same box can carry a different codec entirely, which is the entire reason the two words are not interchangeable even though 'MP4' gets used as a stand-in for both.
That conflation has a real cost the moment a feature question comes up. Whether a file can carry an alpha channel, 10-bit colour or a specific audio format is almost always a codec question, not a container question and not a resolution one — asking whether 'the MP4' supports transparency is asking the wrapper a question only the compression scheme inside it can answer.
It also separates a delivery file from a working master. The H.264-in-MP4 shape most generations arrive in is a reasonable file to publish and a poor one to repeatedly re-edit from — it is typically 8-bit with reduced colour sampling and long-interval compression, so every re-encode compounds loss that was already spent once. A working master uses a codec built to be reopened without that penalty — ProRes and DNxHR are the familiar professional examples — transcoded once from the delivery file and then finished on, rather than re-encoding the same lossy export again on every pass.
In practice
- Treat 'MP4' as an answer to what the wrapper is, not what the compression is — the codec inside is the separate question that actually decides what the file can hold.
- Whether alpha, 10-bit colour or a particular audio track survives is a codec question, not a resolution or aspect-ratio one.
- Re-encoding a delivery-codec file repeatedly compounds loss; keep any file you plan to re-cut in a format built to be reopened.
The mistake to avoid
Assuming two files are interchangeable because they are both '.mp4'. The container says nothing about the codec inside it, the bit depth, or whether a feature like alpha survived — two MP4s can differ on all three at once.
Go deeper
Pick a Mezzanine Codec You Can Reopen
Platform MP4s are not masters. Compare ProRes 422 HQ, DNxHR HQX, and FFV1 for 10-bit 4:2:2, alpha, audio tracks, and a file you can still open in five years.
Related terms
Alpha channel
An alpha channel is a fourth layer of image data, alongside red, green and blue, that records how transparent each pixel is — and whether a file keeps one depends entirely on its format, not on how good the cutout underneath it was.
Resolution
Resolution is how many pixels an output contains, usually named by its height — 720p, 1080p, 4K — and set before generation rather than after.
Upscaling
Upscaling raises the resolution of media you already have, inventing plausible detail rather than recovering detail that was never recorded.
Content repurposing
Repurposing is turning one finished piece into the several format-native cuts each platform expects, rather than posting the same file to all of them.
Hook rate
Hook rate is the share of people shown a video who are still watching a few seconds in — the number that grades the opening, not the edit behind it.
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