Editable codec problem

[Omtech]

HI,

can someone tell me or explain to me the editable format codec and none editable codec?

when I read about none ditable codec in forum I am very confused. I would like if soemone can clarify this to me. Please be always patient with my broken english.

[Rob]

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.

[XTR-91]

DV-AVI, by far, has been the most respected codec in terms of recording and editing. In general, formats with higher amounts of compression require more processing power and sometimes build up lag. Some editing software has been created with decoding systems that are designated to handle MPEG-2 and AVCHD formats – which is good.

Frankly with Cyberlink PowerDirector, I haven’t experienced any other side affects such as long GOP. I’ve tested this theory with MPEG-2, and have been able to make cuts at any frame individually. Of course, my software requires that a single clip be at least 3 frames long. In other words, I’ve been able to make cuts at four consecutive frames (00:00:00:01, 00:00:00:02, 00:00:00:03, and 00:00:0004) – of course not all at once, but you get the idea here. In other words, I can make cuts at practically any position, as long as I “follow the rules”. The same is true for AVI, WMV, and MPEG (MPG-1) formats.

Some editing software is built to handle MPEG-2 and AVI formats in nearly the same way. Just wanted to point that out here.

[birdcat]

FWIW – Sony Vegas Pro can edit AVCHD without a problem if your box is powerful enough. (at least dual core 2GHz, 2 GB RAM).

[Rob]

“I’ve tested this theory with MPEG-2, and have been able to make cuts at any frame individually.”

“Sony Vegas Pro can edit AVCHD without a problem if your box is powerful enough.”

All software can edit AVCHD. All software can edit MPEG. There isn’t anything that physically stops you from cutting up video that has been compressed using Long GOP compression. That’s not what it means when you say a codec is “editable”

To say a codec is “editable” means that codec holds it’s quality from beginning to end, and that doesn’t happen when you cut up Long GOP video because you delete frames that other frames look to for data.

Does that mean your video is going to look absolutely horrid when you cut Long GOP video? No. But it’s a fact that codecs like AVCHD and HDV do not perform as well as DVCPro HD and AVC-Intra.

[birdcat]

Since all codecs are compressed (hence codec = compressor/decompressor) – even DV-AVI, I was under the impression “editable” was a function of whether your NLE could indeed use the source on it’s timeline vs. not (I believe not all NLE’s can edit ACVHD, SWF, FLV, etc…)..

Quality is, in my mind, a seperate function as some codecs, as you have said, are of a higher quality and yield better final results.

[Cville]

I’ll throw this question into the mix as to quality. Is that why you would transcode a piece of video prior to editing?

[XTR-91]

“I’ll throw this question into the mix as to quality. Is that why you would transcode a piece of video prior to editing?”

Some people would rather have the ease of processing you get from editing DV-AVI. Of course, MPEG-2 and DV-AVI use two separate compression techniques, so the losses are entirely different. Having original MPEG-2 converted to DV-AVI, you would have the limitations (losses) of both formats.

“To say a codec is ‘editable’ means that codec holds it’s quality from beginning to end, and that doesn’t happen when you cut up Long GOP video because you delete frames that other frames look to for data.”

This doesn’t necessarily pose a problem for killing frames in the final production. It’s possible that the frames which depend on others draw their data from the original file (not the editor timeline). I’m not saying that this is necessarily the way it works, but I haven’t noticed any of these symtoms – not with my editing software (PDR), anyway.

[Author]

Posts