Codecs for Editing: ProRes, DNxHR, H.264 and HEVC

The short answer

• • To edit: an intraframe codec, ProRes 422 or 422 HQ, or DNxHR SQ or HQ. Every frame decodes on its own.
• • To grade and finish: 10-bit or better: ProRes 422 HQ or 4444, DNxHR HQX or 444, or the camera originals.
• • To save space or cut on a laptop: proxies in ProRes Proxy or DNxHR LB, relinked to the originals at the end.
• • H.264 and HEVC: made for delivery and for cameras that need small files. Editable, but heavier to decode.

Four properties decide how a codec behaves in an edit: whether frames are compressed alone or in groups, the chroma sampling, the bit depth, and the data rate. The rest of this guide takes them in turn, then compares the families with the makers' own figures.

Intraframe vs long-GOP

An intraframe codec compresses every frame on its own. Apple puts it plainly: all ProRes codecs are frame-independent, each frame encoded and decoded independently of any other. DNxHR and DNxHD work the same way. To show frame 1,000 the computer decodes frame 1,000, nothing else.

A long-GOP (group of pictures) codec, the usual way H.264 and HEVC are used, stores a complete picture (an I-frame, built from intra prediction only) every so often, and describes most frames as changes from one or two other frames (P- and B-frames). That is far more efficient, so files are much smaller. The cost is in the edit: to show a B-frame the decoder needs the frames it refers to, so scrubbing, reverse play, multicam and effects all ask more of the machine.

4:4:4, 4:2:2 and 4:2:0

Video codecs store brightness (luma) at full resolution and color (chroma) at the same or lower resolution. The three numbers describe how much color is kept:

• • 4:4:4: full-resolution color. VFX plates, green screen, graphics, and RGB masters.
• • 4:2:2: color at half the horizontal resolution. The usual editing and broadcast format; the ProRes 422 family.
• • 4:2:0: color at half the horizontal and half the vertical resolution. The H.264 High and HEVC Main and Main 10 profiles that most delivery files use.

You rarely see the difference in a straight cut. You see it when you pull a key, sharpen edges in color, or scale and composite: 4:2:0 color edges are softer and keys get ragged. Transcoding 4:2:0 camera files to a 4:2:2 codec makes them easier to edit but doesn't restore color detail that was never recorded.

8-bit, 10-bit and 12-bit

Rules of thumb: record and finish log and HDR at 10-bit or more; keep the bit depth through every transcode (an 8-bit intermediate throws away what a 10-bit camera recorded); and 8-bit is fine for finished SDR material that only needs cutting.

Apple ProRes

ProRes is Apple's family of intraframe codecs, from Proxy for offline editing to 4444 XQ for the highest-quality masters. Apple publishes target data rates in its ProRes white paper; the actual rate varies with picture content, by up to about 10% per frame above the target.

Rates in Mb/s. The 4444 rates are without alpha. All four 422 flavors are 10-bit 4:2:2, and 422 HQ is the workhorse; 4444 and 4444 XQ are the only flavors that carry an alpha channel. For DCI 4K (4096 × 2160) at 24 fps, 422 HQ is 754 Mb/s. The 4K production guide has the 4K and raw figures, and the ProRes data rates cheat sheet puts them on one page.

Avid DNxHR and DNxHD

DNxHD is Avid's HD-only family; DNxHR extends it to any resolution, and Avid now calls the whole thing Avid DNx with five levels: LB, SQ, HQ, HQX and 444. The old DNxHD names were their HD data rates: at 1080p 23.976, DNxHD 36, 115, 175 and 175x are now LB, SQ, HQ and HQX.

Avid publishes these rates in MB/s. They appear to be binary megabytes, judging by the old DNxHD names: converted at × 8.39 to Mb/s, as here, they line up with DNxHD 36, 145 and 220. Avid labels HQ as its 8-bit high-quality level and HQX as High Quality Extended, the level to use for 10-bit and 12-bit YCbCr sources; 444 is the only level for 4:4:4 and RGB. HQ and HQX share a data rate.

H.264 and HEVC

H.264 (AVC) and H.265 (HEVC) are ITU-T standards built for efficient delivery. What a given file can hold depends on its profile, which is worth checking in your clip's metadata:

HEVC is the newer and more efficient of the two, and usually takes more processing to decode. Both edit well on machines with hardware decoding for that exact profile; 10-bit 4:2:2 long-GOP files are the ones most likely to stutter. When they do, transcode to ProRes or DNxHR, or make proxies (see the proxy workflow guide).

Choosing a codec for each stage

CineMath's Data & Storage calculator does this for any runtime: type in the maker's data rate and it gives the size, the record time on a card or drive, or the bitrate that hits a target size. The free bitrate calculator works out the size in your browser. For backups and RAID on top, see video storage planning.

Editing codec questions

Next: if the originals are too heavy to cut, set up proxies with the proxy workflow guide, and size the drives with Data & Storage.