Export ProRes 4444 with an alpha channel
ProRes 4444 is the format editors ask for when a clip has to carry transparency onto a timeline. Transparency Render can produce one in the browser — no Premiere licence, no command-line ffmpeg, no install.
Export a ProRes 4444 MOVWhat the fourth 4 is for
The digits describe the sampling: 4:4:4 means full colour resolution on every channel, with no chroma subsampling to smear the edges. The fourth 4 is the alpha channel — the reason to choose this codec over ProRes 422. Combined with 10-bit depth, it survives repeated re-encoding through a grade or a compositing chain far better than a delivery codec, which is exactly what an intermediate is for.
Bringing it into an editor
The MOV imports directly into After Effects, Premiere Pro, DaVinci Resolve and Final Cut Pro, and the transparency is recognised without any extra step. If a layer appears with a black background instead, the interpretation is wrong rather than the file: check that the footage is set to straight (unmatted) alpha, not premultiplied. Transparency Render writes straight alpha, and guessing wrong is what produces dark fringing around the edges of a subject.
Size is the catch — plan for it
ProRes has no rate control. Unlike H.264 or VP9, it does not target a bitrate and spend fewer bits on simple frames; every frame costs roughly the same, so the file size follows resolution and duration alone. At 1080p with alpha that is around 50 MB per second — about 3 GB a minute.
| Resolution | Roughly | Practical clip length here |
|---|---|---|
| 1080p | 50 MB/s | about 10 seconds |
| 720p | 22 MB/s | about 20 seconds |
| 480p | 10 MB/s | about 50 seconds |
Those limits are the browser's, not the codec's. The finished file has to be assembled in memory before it can be handed to you, and a tab cannot hold several gigabytes to do it. The app estimates the size as you change the settings and refuses an export it cannot complete, rather than stalling part-way through a long encode.
Need more than a few seconds? Export WebM VP9 with alpha instead — same transparency, a fraction of the size, and no length limit worth worrying about. Most editors import it directly, and if yours will not, transcoding a small WebM to ProRes locally is quick.
Getting the most out of the quality setting
The quality slider is a qscale, and lower means better: 2 is close to lossless, 9 is a sensible default, and 20 is visibly soft. Because size scales with it, dropping from 9 to 12 buys noticeably more clip length for a difference few people can see on an overlay or a lower third. Trim to the exact frames you need first — the in and out points cost nothing and save more than any quality setting.
Starting from green screen footage
ProRes 4444 preserves whatever alpha you give it, so the key has to be right before you export. Get the edges clean first — how to remove a green screen cleanly covers similarity, edge blend and despill — then pick the ProRes preset and export.
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