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When to edit native, When hybrid, and When pure i-frame… and Why

Ever since the launch of Final Cut Pro 6.0 (at this writing, we are at 6.04), we have for the first time had the possibility of realtime hybrid editing. Prior to FCP 6.0, in order to have realtime editing we had to convert all footage to the target format (códec, framerate, resolution, etc.) before editing… or edit natively. Now editors need to decide, on a case-by-case basis, whether to edit native, hybrid, or pure i-frame. But let me start by defining my key terms for this article:



Códec

Here is my expanded definition of the word:
(Coder + Decoder… from the Latin codex, -ĭcis, code, and -de, Latin prefix that negates or reverses the base meaning.)

1. noun. Algorithm used to encode and decode sounds, words, text… or audio/video signals.
2. noun. Hardware device or computer program that via a specific algorithm carries out encoding and decoding of sounds, words, text, or audio/video signals.

DV100

DV100 is proper technical name for a códec which Apple and Panasonic tend to call “DVCPRO-HD”… but that practice is confusing and illogical, since DVCPRO-HD is the name of a videotape format, which happens to use the DV100 códec. However, the DVCPRO-HD tape format does not have exclusivity on the DV100 códec, which nowadays is also recorded on P2 cards and hard drives as well.

GOP


In MPEG encoding, frames are organized in GOPs (Group of Pictures). Depending upon the type of MPEG, there may all i-frames (where each frame contains all of the information), or a combination of i-frames and other frames which do not include all of the information for each frame. In that case, the non-i frames need to be reconstructed. All HDV formats use a short, medium, or long GOP, as do all XDCAM-HD and all DVD-video recordings. Long GOP encoding is more efficient, since it offers higher quality at a lower bit rate than pure i-frame encoding, although long GOP recording can be much more demanding on a computer during editing in certain circumstances, as I will explain later in this article.

Hybrid editing


When the source footage’s códec doesn’t match the sequence códec or render códec. In FCP 6.0x, we get a green bar on the upper part of the timeline and we get realtime almost always on a recent Mac, as long as we have set our RT (realtime) setting to “Unlimited”.

i-frame encoding


A type of encoding where all frames are i-frames. This is much easier on a computer processor when editing, but less efficient to record. This means that to maintain low bit rate, more information is thrown away… or a higher bit rate must be recorded to maintain high quality.

Native editing


When the source footage códec and the sequence target códec or editing códec are the same.

Pure i-frame editing


When both the source footage and timeline settings (target format) are both i-frame códecs, although not necessarily the same ones. For that reason, a editing situation can be both hybrid and pure i-frame.

RT-editable format

When I say RT-editable format, I mean a códec that FCP can accept as editable in realtime. These include both long GOP and i-frame códecs.

Sampling


Color sampling is measured as 4:4:4, 4:2:2, 4:2:0, 4:1:1, and 3:1:1. In general, the higher color sample, the better. However, be careful when a format or códec is promoted as having 4:2:2 color sampling only to discover later on that the 4:2:2 sampling was achieved after heavy subsampling. It’s easy to poll 25% of your neighborhood about the upcoming election when you truly poll 25% of only 66.6% of the people who live there! When you read ahead, you’ll know to which códec/format I’m referring.

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