What makes a codec “editab

#173793
AvatarRob
Participant

What makes a codec “editable” is that codec’s method of video compression. There are two types of compression: Intra-frame (or i-frame) and Long GOP (or interframe).

Long GOP means “Long Groups of Pictures.” Think of it as long groups of video frames. Simply put, when a codec uses this method of compression, the frames within a group share data with each other, therefore, frames do not have to be fully encoded because they can look to other frames and “reuses” their data. This is how some HD codecs achieve small file sizes, but consequently lower quality as well.

Intra-frame is simple. Each frame is encoded with ALL of the the necessary data it needs. The video frames DO NOT have to look to other frames for data, but you do get larger file sizes.

So which method of compression is better for editing? The answer is Intra-frame. See, when you start cutting up Long GOP video while you edit, you begin deleting frames that other frames were referencing for necessary data, and when you do that you force the video frames to look to less ideal frames for data it no longer has, resulting in even worse quality. Long GOP is also more taxing on your CPU because it has to look at many frames to display the video while with Intra-frame your CPU only has to worry about looking at one frame of video.

Here are some recording codecs that use Long GOP: XDCam EX, HDV, AVCHD, and MPEG2

Here are some recording codecs that use I-Frame: DVCPro HD, AVC-Intra, and almost all SD codecs.

If you find that you have recorded one of the codecs that uses Long GOP compression, you must transcode your video to another format that uses I-Frame compression before you edit (unless you plan to export in the same codec you recorded). If you use Final Cut Pro, many people transcode to ProRes. Avid uses DNxHD. If you do not use either of these to software solution, I’ve read that people have successfully transcoded to DVCPro HD and edited happily with no problems.

At first this seems like a complicated issue, but once you let it all sink in you’ll find that it makes sense.

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