How compression rates and codecs affect your visual effects

How Compression Rates and Codecs Affect Your Visual Effects

How Compression Rates and Codecs Affect Your Visual Effects

The understanding of compression rates and codecs can take your VFX game to the next level.

Sometimes it can be tempting to use your VFX software’s built-in codec presets for every project, but knowing the role compression rates and codecs play in producing the best visual effects possible is paramount to becoming a successful VFX producer. 

No matter what stage you’re at in production, you’ll always be deciding which codecs and compression rates to use during import and export.

Today, we’re going to look at the necessity of certain types of compression rates in different scenarios, and give you a few practical tips to help you get a deeper understanding of how codecs interact with your VFX footage.

How Do Video Codecs Work?

This seems like a fundamental question, but it’s one that is important to understand correctly. Cameras use different types of video codecs that are optimized for their hardware to capture the best image possible. 

Thanks to advances in digital video codecs within modern cameras, we now have mainstream access to RAW or Log files, which typically bring in the least compressed version possible of the captured data (though it’s technically not 100% lossless). It allows for the most flexibility possible in post-production.  

However, this data isn’t like a normal playable video format. It has to utilize a video codec to actually be played back on a computer.

Once the RAW file has been converted to a codec for playback in software, it can be edited and then exported for viewing via other codecs which are optimized for the video’s destination devices. 

Blu-Ray, DVD, broadcast formats, and formats for movie theaters (like DCP) are all examples of destinations that need to be properly encoded for.

If you’re uploading your video to the web, your video is going to be compressed again even further by the hosting service for optimum efficiency on its platform (like YouTube or Vimeo). 

Once the video goes from the camera to the audience, it’s been compressed numerous times - which is why taking into account codecs and compression rates during the VFX process are so critical to ensuring the best quality in your final product.

The codec workflow can generally be boiled down to these stages:
You can see at each stage how many times the video gets ran through some type of compression/codec, and that’s not even counting how broadcasters or online platforms additionally re-encode your final product. 

Just like making multiple copies on a copier, you want your source to be the best quality possible, not make successive copies one iteration at a time.

Having said that, there are times that you don’t necessarily need the highest quality footage at every phase of post-production. Proxy files can help tremendously when working on a project, and you might not even be able to notice a difference between certain, more efficient codec.

Always be cognizant of how many times your footage may end up getting compressed after it leaves your workstation.

Have a Codec Game Plan in Place

Communication is critical in the production pipeline, and as a VFX artist, it’s a very good idea to know where your assets are coming from, and where your exported files will be heading. The day you begin your visual effects work isn’t the best time to start thinking about codecs. 

Talk to your supervisors and editors before you receive your shots and decide which codecs and formats you’ll be using throughout each step of post-production - i.e., what you’ll be receiving and what you’re expected to export your VFX as, and stick to that plan.
Emerson College Post Production Labs: VFX Workflow Guide

Which Codecs are Best for VFX?

For VFX work, you’ll typically want the most uncompressed file you can get your hands on for keying, tracking, compositing, etc. Muddied pixels or even the slightest artifact can interfere with a successful key or track, so get the best file you can. Something like ProRes 422 HQ or DNxHQX are great.  

A general rule for VFX is, if it’s available, opt for the original codec straight from the camera. 

If you’re receiving footage that has already been color graded, it’s still a good idea to ask for the original footage from the camera to do complex work. Once the heavy lifting is done, you can swap the base video layer for the graded one.  

There are ideal codecs for editing and color grading, but for VFX work, some of the primary areas you don’t want to skimp on are chroma subsampling and bit depth. They make a big difference in your ability to deliver quality results.

The video below explains quite elegantly how the overall codec encoding process works from start to finish, and does a great job detailing chroma subsampling and bit depth.

How to Export Clips to a VFX Artist

If your editors want to see best practices for exporting their clips to you in Premiere Pro, the video below gives them a thorough explanation on why you need the type of clips you do, and how to prep their footage before sending to the VFX department.

How to Export VFX Clips

Once you’ve finished up your VFX, the hardest part is over. Emerson College’s Post Production Labs explains the best route for exporting VFX from After Effects like this:
"Getting your project out of After Effects is just your normal exporting process. Add each clip to the render queue, via Composition > Add to Render Queue, or Composition > Add to Media Encoder Queue. Make sure to consider where your renders will be going. High quality codecs such as ProRes422, ProRes4444, or Animation are suggested in most scenarios. Both ProRes4444 and Animation can preserve color information and carry an alpha channel. Though as its name suggests, Animation is best-suited to animations, not live action footage. After exporting, simply relink in your NLE and do your final export."
We’ve only scratched the surface when it comes to the technical logistics of codecs and compression. If you’d like to learn more, check out this comprehensive look at video codecs, compression rates, and how to choose the right ones for your project available from the great folks at FrameIO

If you enter your e-mail address, they’ll even provide you with a free 53-page e-book on codecs “from capture, to edit, color, and delivery.”  

We hope this article has given you a better understanding of how codecs and compression rates interact with VFX footage. Begin learning the encoding process, and make a few specialized encoding presets that fit your needs best, then share them with your VFX team!

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