VFX File Formats You Need to Know to Save Time and Space
Working in the world of visual effects (VFX) means dealing with a virtual hodgepodge of assets that get created. From 3D renders, proprietary files, still images or even video footage straight from a camera, there's a lot of file formats out there that can be used with some measure of success in just about any VFX software. Despite this, it doesn't really matter what compositor you're using, you can either cause yourself a lot of time and frustration or save yourself a lot of time and frustration depending on what file format you choose to work with on a daily basis.
If you look at the image above, which of the jars would you say is complete? The best way to know if a jar has everything in it is to put a label on it. The label tells you both of the jars should have 200 jelly beans in them, and it isn't hard at all to tell which jar actually has everything in it that it is supposed to have.
While obviously over simplified, this is basically the same way a computer works. When software creates a file, think of it like jelly beans being put into a jar. As data is put into the file by software, there is a "label" that keeps track of what should be there.
This "label" essentially amounts to an index of the data in the file. Just like you're able to glance at the image above and see which of the containers isn't complete by looking at the label, software knows when a file isn't complete when either the data inside doesn't match the index or the index itself is missing completely.
This is important to know because when you're rendering out a video file, all of that data is going into one really big file. If at any point the software has an error that causes the render to crash, the "label" won't match what's inside the file and the software will know something is missing. While it may be easy to add the missing candy in a container, as in the example above, for a computer the only way to append data to an incomplete file is really to just start over. This means re-rendering the file.
If you've rendered anything before, you know rendering can be quite a time-consuming task. It's common for a single frame to take hours to render. Because a video file is a single file that contains all of your project's frames, any time there any errors that cause an incomplete file it, means you need to re-render the entire video file.
Then again, instead of rendering out one really big video file you can render out a bunch of smaller image files where one image file equates to a frame of your project. When the inevitable happens and the render crashes, you'll need to re-render the entire file exactly the same as if it were a video file, but instead of this re-render being all of the frames it's just the image files for the frames that crashed.
So let's do some simple math to see why all of this means you need to be rendering image sequences instead of video files.
Let's say you're rendering out a sequence that is 30 frames. If each frame takes one hour to render, that's 30 hours to complete the render. Until those 30 hours are done, the file is still incomplete and is still getting data put into it. If frame 29 has an error causing the render to crash with a video file, that means you'll need to re-render the first 28 frames that didn't have any errors in order to get the file to complete. That's 28 hours wasted.
In the same scenario with an image sequence, after each frame was rendered the image file for that frame would be completed before moving onto the next frame. So you'd only have to re-render the last couple of frames (frames 29 and 30). Of course that's a simple example, but by rendering image sequences you're able to pick and choose which frames you want to render without having to render all or nothing as you do with a video format. Rendering image sequences can quickly add up to a lot of time saved simply by changing the format you choose and, by extension, could easily mean the difference between the success or failure of a project hitting its deadline.
Always Render Image Sequences
Before taking a look at some of the file formats themselves, it's important to immediately remove all of the video formats from this equation. One common misconception is because a compositing program deals with moving images means the only file formats that should be used in a compositing program are video files like MOVs or AVIs. While video files have their place and it's important for you to know about them because you'll no doubt have to work with them at some point, generally speaking that place is not in a VFX pipeline. There are numerous reasons for this, but most of them can usually be boiled down to one really big reason: Renders tend to crash. As frustrating as it may be, it doesn't matter if you're using a budget system at home or a powerhouse workstation, every VFX artist has had renders crash.
If you look at the image above, which of the jars would you say is complete? The best way to know if a jar has everything in it is to put a label on it. The label tells you both of the jars should have 200 jelly beans in them, and it isn't hard at all to tell which jar actually has everything in it that it is supposed to have.
While obviously over simplified, this is basically the same way a computer works. When software creates a file, think of it like jelly beans being put into a jar. As data is put into the file by software, there is a "label" that keeps track of what should be there.
This "label" essentially amounts to an index of the data in the file. Just like you're able to glance at the image above and see which of the containers isn't complete by looking at the label, software knows when a file isn't complete when either the data inside doesn't match the index or the index itself is missing completely.
This is important to know because when you're rendering out a video file, all of that data is going into one really big file. If at any point the software has an error that causes the render to crash, the "label" won't match what's inside the file and the software will know something is missing. While it may be easy to add the missing candy in a container, as in the example above, for a computer the only way to append data to an incomplete file is really to just start over. This means re-rendering the file.
If you've rendered anything before, you know rendering can be quite a time-consuming task. It's common for a single frame to take hours to render. Because a video file is a single file that contains all of your project's frames, any time there any errors that cause an incomplete file it, means you need to re-render the entire video file.
Then again, instead of rendering out one really big video file you can render out a bunch of smaller image files where one image file equates to a frame of your project. When the inevitable happens and the render crashes, you'll need to re-render the entire file exactly the same as if it were a video file, but instead of this re-render being all of the frames it's just the image files for the frames that crashed.
So let's do some simple math to see why all of this means you need to be rendering image sequences instead of video files.
Let's say you're rendering out a sequence that is 30 frames. If each frame takes one hour to render, that's 30 hours to complete the render. Until those 30 hours are done, the file is still incomplete and is still getting data put into it. If frame 29 has an error causing the render to crash with a video file, that means you'll need to re-render the first 28 frames that didn't have any errors in order to get the file to complete. That's 28 hours wasted.
In the same scenario with an image sequence, after each frame was rendered the image file for that frame would be completed before moving onto the next frame. So you'd only have to re-render the last couple of frames (frames 29 and 30). Of course that's a simple example, but by rendering image sequences you're able to pick and choose which frames you want to render without having to render all or nothing as you do with a video format. Rendering image sequences can quickly add up to a lot of time saved simply by changing the format you choose and, by extension, could easily mean the difference between the success or failure of a project hitting its deadline.
