Choppy playback

[Jon Barrie]

Hi Jason,

This is one of the single most mis-understood aspects to working with digital video. Compressed Vs Uncompressed. And then where the bottle necks are in relation to bitrates.

Before I get into details, Avid is converting to a compressed format it can handle, you may need to convert your material to something similar but maybe not…

Have you tried to lower the % of the program size to say 25% or 50%, then set the playback quality to Half or even Quarter. It’s not a representation of the final quality it’s just to get you editing. I find 25% scale with 1/4 or 1/2 (without any effects) is sufficient for most of my work – and using external drives for my media… now onto some details.

SD res Uncompressed can be watched back and worked with in it’s uncompressed form on standard internal drives, just. It is best done with a RAID 0 or RAID 5 setup using 7200rpm speed drives.

HD on the other hand in Uncompresssed has not just got a larger bitrate to watch back 1 sec of material, but the processing speeds of CPU, RAM and HDD bitrate limitations are very much not run of the mill. If any 1 of the 3 mentioned areas are not upto the bitrate task then you will have playback problems when attempting to play in Full resolution. Hard Drive read/write speeds are most likely the bottle neck here.

There are specs on the bitrate ranges for SD and HD Uncompressed (which Animation codec in a QT wrapper is) and then for material with an Alpha Channel goes up again! Do a little research if you want the details. But a “standard” (Sold to Joe Blogs at home user) computer setup will never be able to keep up with Uncompressed HD, or SD properly for that matter.

AVID has it’s own compressed codec that it’s systems are optimised to understand which has a far less bitrate and therefore the HDD bottle neck or any other areas (RAM, CPU) aren’t being pushed anywhere near as hard. FCP have this scenario too with their ProRes codec.

The other hand compression that is very in bitrate, but amazing in perceived quality like H.264 is very taxing on the CPU, so getting the optimization to work with it natively (such as HDSLR clips) is critical to the process. HDD bitrate speeds again will make a huge difference to speed.

Using a RAID 0 or RAID 5 only for media is the recommended workflow. Holding the Media on the Operation System Hard Drive is just asking for trouble as the CPU and the Drive and the RAM need to work with the Operation System first, then the Applications that are running, then the Media itself while trying to juggle all the different sectors the OS, Apps and Media are on the drive the speed of the HDD is diminished and so is playback.

Separate drives for OS/Apps and Media Cache/Media/Projects is the minimum recommended workflow.

I hope this gives you and others that read this a small insight into why something works on one system and not another and how HDDs need to have enough read/write speeds for HD work, compressed and especially with Uncompressed (which no one really “edits” with).

– Jon Barrie 😉

Jon Barrie
aJBprods
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[Jason Boekeloo]

Thanks, Joe, for the help! It seems to me this is a weakness of Premiere Pro, a lack of a viable compression format. I’m not an editor but sometimes some simple editing is required and I own the CS5 production bundle so I figured I’d rely on Premiere but it certainly has its drawbacks.

That being said I turned down the playback resolution to 1/4 and it’s helped. I also realized my media wasn’t on my RAID drive so moving it over helped as well.

Again, thanks for the advice.