Alright, you’ve shot your film, and you’ve got all of your files onto your computer. Now you need to decide whether you’re going to edit with these files, or whether you want to transcode into another format.
Why should I transcode before editing? Can’t I just edit the files that came out of the camera?
Well, it depends. Pretty much all of the major software packages can now edit any codec that your camera creates, (unless you’re a badass shooting on a brand-new camera with brand-new technology). But while it’s almost alwayspossible to edit the codecs that your camera shot, it’s not always the best idea.
If you are lucky enough to be shooting on a codec that is great for editing (see the codec chart), then you can skip this step.
For many of us, however, the capture codec isn’t going to be optimized for editing. There are two main factors you need to consider when choosing your edit codec: compression type and bit rate.
1. Highly-Compressed codecs can Slow Down Your Editing
Most lower to mid-range cameras record with codecs that use temporal compression, also known as long-GOP compression.
The simple explanation of a long-GOP is that, for each frame, the codec only captures what has changed between this frame and the previous frame. If the video doesn’t include a lot of motion, then this means that the new file can be a LOT smaller than the original. The difference between this frame and the last frame is just a few pixels, so all you need to store is a few pixels. That’s great!
The issue, however, is that these codecs tend only to work well when played forward.That’s great for viewing on YouTube and your DVD player, but it’s not great for editing, because when you’re editing you’re often jumping around, or playing a clip backward. It takes a lot more processing power to do those things quickly with a long-GOP codec. A high-end computer might have no trouble, but even a mid-range computer will lag and stutter when you skim through the footage quickly or jump around.
Codecs that aren’t long-GOP (a.k.a. Intra-frame codecs), however, can play backwards just as easily as forwards, and even a mid-range computer can skip around very smoothly. If you’ve only ever edited clips straight from the camera, you not might realize what you’re missing!
The other thing that can cause issues with playback is raw video. Raw video needs to be converted before it can be displayed (sort of like a codec does), and some computers can’t decode the raw file fast enough, especially if it’s 4K. Ironically, both the low-end cameras and the highest-end cameras produce files that are hard to edit!
2. High-Bitrate codecs can Slow Down Your Editing
For low to mid-range codecs, you don’t have to worry about the bitrates at all. Once you start moving up the ladder, however, high bitrate codecs can cause issues with editing, especially if you’re working on everyday computers.
The reason is because your computer needs to be able to read the data from your hard drive at a bitrate that is at least as high as your codec’s bitrate. It makes sense — if your codec is 50Mb/s (fifty megabits per second), then your computer needs to be able to read that file from your hard drive at 50Mb/s or else it’ll fall behind and stutter.
(note that Mb/s stands for megabits per second, while MB/s stands for megabytes for second. There are eight bits in a byte, so you need to multiple by 8 when converting from MB/s to Mb/s)
The good news is that hard drives are getting faster every day, so 50Mb/s is never going to cause any problems. But what if you’re editing ProRes 422HQ at 4K, which is 734Mb/s? The average external hard drive is only just barely fast enough to play that back, and some cheaper hard drives won’t manage it. And then, what if you’re editing a multicam with three cameras? Suddenly you need 3x that data rate: 2,202Mb/s! At that point, you’re going to need to invest in some high-performance hard drives or RAIDs.
Here are some rough guidelines for common data storage speeds, though of course there will always be certain models that underperform or overperform.
Standard spinning drive: 100-120MB/s
Professional spinning drive: 150-200MB/s
Standard SSD: 400-500 MB/s
Low-end RAID: 200-300 MB/s
High-end RAID: 1000-2000 MB/s
https://blog.frame.io/2017/02/15/choose-the-right-codec/#codec-shoot
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