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.
The H.264 MP4 you posted is a delivery. It is not a master. Reopen it in six months for a recut and you will grade on 8-bit 4:2:0 with a long GOP, then compress it again. Pick a mezzanine you can actually reopen: ProRes 422 HQ as the default, DNxHR HQX if the shop is Avid, and FFV1 in Matroska as the archive exception.
A mezzanine is an intermediate: intra-frame or visually lossless, 10-bit, 4:2:2, with audio you have not folded into AAC. You transcode the generated file into it once, you finish on it, and every platform encode comes from it. The generated MP4 is a source. The social MP4 is a child. Neither is the thing you keep.
Platform MP4s are not masters
Generated clips typically arrive as H.264 (sometimes HEVC) in an MP4, 8-bit, 4:2:0, long GOP. That shape is a reasonable ingest for an editor's first look. It is a poor file to grade, recut, legalize, grain, and re-encode from, because every one of those steps is another generation of loss on a codec that already threw away chroma and already averaged across frames.
Handing generated clips to a human editor argues for a clean H.264 handoff so an NLE opens the pile without a warning dialog. That is a handoff recommendation, for the first assembly. The mezzanine is what you transcode into once the cut is real, before the grade gets serious, and it is what you archive when the job closes.
Transcoding an 8-bit 4:2:0 source into a 10-bit 4:2:2 mezzanine does not invent chroma that was never there. It stops further 8-bit rounding, and it gives the grade, the legalizer, and the grain node a file that will not add long-GOP artefacts every time you scrub. Be honest about the promotion: you are protecting what you have, not restoring 4:2:2.
Check what you actually received before you pick a flavour. The browser-side video metadata inspector runs on your machine and never calls a model: codec, frame rate, resolution, duration. Use it on the generated file and on the mezzanine you write, so the archive folder does not contain a mystery.
Three codecs that reopen
| ProRes 422 HQ | DNxHR HQX | FFV1 (v3) in Matroska | |
|---|---|---|---|
| Spec | Apple ProRes, documented by Apple | SMPTE ST 2019-1 (VC-3), resolution-independent profile | IETF RFC 9043 |
| Bit depth / chroma | 10-bit 4:2:2 | 10-bit (12-bit available) 4:2:2 | Lossless; 10-bit 4:2:2 is a common preservation choice; RGB 4:4:4 when you have it |
| Alpha | No. Step up to ProRes 4444 | Not the point of HQX. Use DNxHR 444 for RGB plus alpha | Yes, when you encode with an alpha-capable pixel format |
| Compression | Visually lossless, intra-frame, ~220 Mbps at 1920×1080 29.97 fps (Apple's published target) | Visually lossless, intra-frame, finishing flavour of DNxHR | Mathematically lossless, intra-frame |
| Audio | PCM in QuickTime | PCM in MXF or QuickTime | PCM or FLAC in Matroska |
| Who opens it in five years | Anything that still ships a ProRes decoder (FCP, Resolve, Premiere, many NLEs) | Anything that implements VC-3 | Anything that implements RFC 9043. FFmpeg is the reference |
Apple is explicit that ProRes 4444 and 4444 XQ are the only ProRes codecs that support alpha. If the job is keyed type, a generated matte, or a graphic stack, 422 HQ is the wrong flavour. Same idea on the Avid side: HQX is the 4:2:2 finishing codec; 444 is the RGB/alpha one.
FFV1 is lossless. The Library of Congress Recommended Formats Statement lists FFV1 in Matroska as a preferred format for file-based video. That is the archival argument, not a speed argument. FFV1 files are larger than ProRes 422 HQ on photographic pictures, smaller than uncompressed, and they decode in FFmpeg rather than in a vendor SDK.
10-bit 4:2:2, alpha, and audio tracks
10-bit. A grade, a legalizer, and a grain node all create values between the 8-bit codes. If those operations happen on an 8-bit timeline, they round. 10-bit 4:2:2 is the minimum that makes a Rec.709 64–940 working range real rather than notional.
4:2:2. Generated sources are usually 4:2:0. The mezzanine still wants 4:2:2 so titles, keys, and any subsequent chroma work do not have to 4:2:0-round at every bounce. You are not recovering the missing chroma from the source. You are stopping the rest of the pipeline from discarding more.
Alpha. Most generated video has none. The moment you composite, you need a codec that stores it. ProRes 4444 (mathematically lossless alpha, up to 16-bit) or DNxHR 444. Do not invent an alpha channel in 422 HQ; it cannot hold one.
Audio tracks. Keep PCM on the mezzanine, discrete tracks, at the sample rate you mixed. Fold to AAC only on the delivery encode. A voiceover, a music bed, and a mixdown can all live on the same mezzanine. If you collapse to a stereo AAC inside the "master," the next recut starts from a lossy mix.
Frame rate and resolution. One rate, one raster, for the whole job. Versely timelines default to 25fps; most models that expose a rate offer 24, 30, and sometimes 60. Conform before you write the mezzanine, or the archive is a mix. Resolution is a generation choice; the mezzanine should match the sequence, not upscale "for the archive" without a reason.
Metadata. A mezzanine that strips provenance is a worse archive than an MP4 that kept it. Content credentials through a real pipeline is the C2PA version of that warning. A metadata preservation clause is the contractual one. Whatever you write into the mezzanine, inspect it on the way out.
File size is the objection people use to skip this step. The browser-side video file size calculator will show you the arithmetic before you fill a disk. At Apple's approximately 220 Mbps target, an hour of 1080p29.97 is on the order of 100 GB; 25fps is a little less. That is the disk a file you can grade twice occupies. An H.264 "master" is smaller and used up.
A default and one archive exception
Default: ProRes 422 HQ. 10-bit 4:2:2, intra-frame, visually lossless through the generations a finishing job actually applies, and every common NLE opens it. Use it for generated work that is SDR, has no alpha, and will be recut or re-graded. If the shop is Avid-first or Windows-first and already standardised on DNx, DNxHR HQX is the equivalent default, not a downgrade. Pick one per shop so the archive is not a coin flip per job.
Exception: FFV1 version 3 in Matroska, when the file is the archive. Lossless, openly specified in RFC 9043, listed as a preferred format by the Library of Congress for file-based video. Use it when you will not reopen the file in an NLE every week, and when "visually lossless" is not the promise you want to make to a future you. Keep PCM or FLAC alongside it in the same MKV.
Write the mezzanine after the picture is conformed and before you encode for a platform. Grade, legalize, loudness, grain on the mezzanine. Social MP4s, HLS rungs, and broadcast files are children. If you only keep the child, the next job starts from a compressed copy of a compressed copy of an 8-bit 4:2:0 generation.
The Versely editor is an EDL-based timeline for assembly. Its preview: true pass renders at 480p with a short per-user cooldown, and a single charge applies to the final export regardless of clip count. That export is a source for the mezzanine, not the mezzanine. Transcode the export into ProRes 422 HQ (or HQX, or FFV1) in the finishing tool, then lock that file in the job folder with the shot log.
A default you can say out loud in a kickoff:
Working master is ProRes 422 HQ, 10-bit 4:2:2, PCM audio, one frame rate. If we have keys, ProRes 4444. If this is the deposit copy, FFV1 v3 in Matroska.
Then do not deliver the H.264 as if that sentence had been about it.
FAQ
Can I use ProRes 422 (not HQ) to save space?
Apple publishes ProRes 422 at roughly 66 percent of HQ's data rate, about 147 Mbps at 1920×1080 29.97 fps. It is still 10-bit 4:2:2. For an offline, it is fine. For a finishing master you will grade, legalize, and grain, HQ is the published "visually lossless through many generations" flavour. The disk you save is the headroom you will want on the second recut.
Does wrapping H.264 in MOV make it a mezzanine?
No. The codec is the mezzanine, not the container. Long-GOP 8-bit 4:2:0 in a different box is still a delivery file. QuickTime and MXF are how ProRes and DNxHR travel; they are not a quality upgrade for the H.264 you already have.
What if the NLE will not open FFV1?
Then FFV1 is the archive, not the working default, which is why it is the exception. Finish on ProRes 422 HQ or DNxHR HQX. Write FFV1 as a deposit copy when the job closes, and keep the ProRes as the file you expect to reopen next quarter. An archive nobody's NLE opens is still an archive. It is a bad working master.
Should every generated take be a mezzanine, or only the locked cut?
Only the locked cut, plus any take you know you will finish. Transcoding forty rejected generations into ProRes 422 HQ is how you fill a disk with footage you already replaced. Keep the generated MP4s as sources. Write the mezzanine when the sequence is real.