Chapter 8. Understanding Formats and Codecs

Understanding Formats and Codecs

By Michael Britt

Recall that Chapter 3 talked about how the files coming out of DSLR video cameras like the Canon 5D Mark II and 7D are compressed using H.264. The H.264 files coming out of a Canon camera are compressed 30 times. This is what makes them hard to work with in editing suites. The video frames have to be uncompressed before being rendered, and this process eats most computers alive, causing choppy playback and crashing. Most editing software works better if the compressed files are converted to an uncompressed file type that the software can work with natively. This process is called transcoding and depending on how fast your computer is, can take longer than it did to shoot the footage. This chapter covers transcoding and understanding other formats and codecs.

H.264 Tastes like Chicken

H.264 is a codec that’s used to shrink down high-resolution video for storing, viewing, or delivery. Think of the codec as the cookbook and H.264 as the chicken section. In a cookbook, there are many ways to prepare chicken. You can fry it, bake it, broil it, make soup from it, and so on. The list goes on. The same is true for video. You can burn it on a DVD, broadcast it, stream it on the Internet, make QuickTime movies for iPods, and on and on. You take the same ingredient—chicken or video—and “cook” it into something that can be consumed in different meals or in the case of video, different media applications.

H.264 is a finished (cooked) format, just as fried chicken is cooked from raw chicken. The fried chicken is finished and ready for consumption. You might be able to watch uncompressed video on the web if you have huge bandwidth and time on your hands just like you can eat raw chicken if you want to, but there are better options.

H.264 Tastes like Chicken

H.264 is like cooked chicken, in a way

The H.264 video format has a very broad application range that covers all forms of digitally compressed video, from low bit-rate Internet streaming applications to HDTV broadcast and digital cinema applications with nearly lossless coding. With the use of H.264, you can achieve bit rate savings of 50% or more. The typical H.264 compression level for distribution is 10 times. However, since the formula (or recipe) coming out of Canon video HDSLRs is 30 times, an editing program will have to work harder to smoothly play back the compressed footage.

Transcoding Your Video Files

So what do you do with these heavily compressed video files? You will probably want to transcode (change the file type) them into something that plays well with your editing program and offers a bit of overhead when making color corrections. The general consensus is to convert the H.264 files into Apple ProRes 422. Before I get into ProRes versus other file types, let’s talk about the 4:2:2 designation.

The files currently coming out of Canon HDSLRs are chroma sampled at 4:2:0, which means that the bottom row (b in the formula or zero in 4:2:0) is forced to display the information from the sampling above it. So instead of 16 pixels sending eight color and brightness settings to the processor in a 4:2:2 scenario, the 4:2:0 formula sends only four sets of data for display. This chroma sampling is on top of the 30 times compression in the H.264 codec, so you can see that you would want to be careful with these files once you start to make large color-correction moves in post.

Now that you understand the basics of compression and chroma sampling (whew), you can start making some decisions about how to approach your workflow.

The Video Workflow Chain

The video workflow chain starts at camera setup in the Picture Styles menu. It’s there that you determine the “look” that you will be writing to card in the H.264 finished format. There are a lot of opinions floating around the “Intertubes” about how to get the most out of HDSLR files, specifically the Canon files. Everyone, from Vincent Laforet and Philip Bloom to Shane Hurlbut and Rodney Charters, has a special sauce for this process. Shoot super flat, shoot faithful, shoot neutral with sharpness and contrast dialed all the way down, and so on.

It was also very evident at PhotoCine Expo 2010 that each speaker had his or her own way of doing things that often contradicted the speaker before or after her at the expo. The answer is that they are all right and you have to find the solution that best fits your specific needs.

In the early days of the transition from analog film to digital still photography, the common wisdom was that you had to shoot digital images flat to get a proper exposure. This was a widespread misconception that has since been debunked. It turns out that the only real secret to capturing a great digital file is to properly light and expose the scene for the capture media being used, whether it’s slide film, negative film, or digital chips (shocking, I know).

Workflow for the Everyman

We are in the early days of the DSLR filmmaking revolution, and everyone looks to film/DI (digital intermediary) workflows that have been established for multi-million dollar projects using very expensive cameras that involve many steps and a multitude of specialists. This work-flow compartmentalizes the jobs of Cinematographer, Camera Operator, Camera Assistant, DIT, Colorist, Editor, Lab, and so on. The person exposing the film will not necessarily be involved in every step of this process. The workflow that makes sense in this world is to capture a scene with a wide latitude with a lot of overhead to make corrections in post. Final color looks are rarely “baked-in” on the set.

Then comes inexpensive video-capable DSLRs and the world of micro production and film-making is opened up to a much wider audience. The barrier to entry for creating high-quality cinema-style motion images is lowered, and many photographers find themselves already owning the gear needed for digital filmmaking.

The tricky part has been figuring out the photography/cinematography (PhotoCine) workflow. Photographers search out information on the web in places like DVXUser and other video forums and start piecing together a process that has trickled down from film/TV where the budgets are high and the workload is spread out. This information is adopted on photographer-centric filmmaking forums, and there is suddenly a common wisdom that has taken root (remember the common wisdom/misconceptions for digital stills?).

My problem with this workflow is the fact that files coming out of HDSLR cameras are heavily compressed and use a small chroma sampling. The advice that color experts are giving seems to be counterintuitive to me as a digital photographer. Would you tell a newbie still photographer to shoot her JPEGs flat and correct in post? No, you would tell her that since the look is baked in due to lossy compression, she should treat JPEGs like she would transparencies—getting as close to a final image as possible. My friend Tom Stratton and I have had this discussion many times and end up feeling like outsiders in the HDSLR workflow world. I have spoken with many post-production people whom I trust who tell me not to worry about the compression and reassure me that shooting flat and correcting in post is the way to go.

I am sure that if you are shooting a feature film using a dozen cameras, the shoot-flat workflow could be advantageous, but if you are a still photographer using one or two cameras for a motion ad campaign, you might want to think differently. You would probably want to shoot as close to the final look as possible to minimize the amount of post work and limit problems in the image files by not having to make major color/contrast adjustments later. As a matter of fact, the H.264 format is a finished format designed for uploading to the Internet, so if you needed to, you could deliver quick dailies straight out of the camera without going through any post process. If you shoot flat and correct later, the dailies will have to go through transcoding, color correcting, and then output encoding. Skipping steps to deliver quick uncorrected clips to the client can be a recipe for disaster.

For example, a producer friend was working on a feature for a big studio using a RED ONE camera for the first time. The show was being shot out of town, and the dailies were being sent back to Hollywood uncorrected due to time constraints. Keep in mind that the RED files are close to being in a RAW format and the workflow is usually to shoot flat and process the look in post. The studio freaked out and wanted heads to roll because they thought the dailies looked terrible. I explained what I thought was happening, and that information was sent up the chain to help ease tensions and start a dialogue with the DP and DIT. Of course, the RED footage looked amazing once it was color graded and everyone was happy. The funny part was that another of their out-of-town projects was being shot on Canon 7Ds, and the dailies were coming in great because the look was at least partially baked in during production. The point here isn’t that Canon is better than the RED. It’s that you can’t rely on the kindness of strangers to understand workflow shortcomings due to time constraints and delivering a flat file could cost you work. You would think twice about delivering uncorrected still photos to a client, wouldn’t you?

Finding the Best Approach

My friend Neil Smith at HdiRAW works in Hollywood has a saying that deliverables determine the prep. What that means is that once you know your final output (film out, digital projection, Blu-ray, DVD, web, iPod, and so on), you can then determine what camera and workflow best maximize your needs and budget. I know that those of you reading this are shooting amazing footage that you expect to someday be shown to the Academy on an IMAX screen converted to 3D. For you guys, money is no object and making every shoot into a big production isn’t a problem. But for those of us doing it ourselves as a one-man-band on small projects being tagged onto photo shoots that are destined for the web, there might be a more practical work-flow. One that revolves around making decisions during the shooting process and baking in the look to maximize image quality and minimize time spent in post.

I am not advocating that in every instance, everyone shooting HDSLR footage should burn in the look and bypass grading in post. What I am saying, is that the project should determine the workflow and color-grading in post is not the only option—especially for photographer film-makers who are new to post production and working on minuscule budgets with quick turnarounds.

In a controlled environment like on a studio or a set, you have the opportunity to burn in the look and limit your post workflow, which incidentally can give you a cleaner end product since you’re not making large correction moves in post. These files coming out of DSLRs are optimized for loading to the web, so if you take the time upfront to set the look, you can immediately deliver QuickTime dailies that can be uploaded to the web, iPhone, or iPad, or handed off on a drive or disc.

Consider this quote from Shane Hurlbut, ASC, from his blog:

“With this amazingly inspiring HDSLR technology, I find I am going back to my filmmaking roots and doing it more in-camera. The power is back in the hands of the still photographer and the cinematographer and not as much with the DI colorist with his RAW files and infinite color range. Bake it in and unleash your creativity!”

Ask yourself, why am I approaching my work the same way as a feature film and is that approach necessary? Can I think differently and slow down to make the necessary adjustments on the front end of the video process? Pulling out a camera and shooting tons of footage with the plan to clean it up later is called “spraying and praying” in the still world. If your budget is so low that you don’t have the time or the help to do some of the work up front, where is the money coming from to pay for all the post work? There are always workflow tradeoffs. You either spend the time up front or on the back end, but the time has to be spent somewhere. You just have to choose how many of your resources are allocated to which end of the workflow chain.

The Takeaway

The Takeaway

As a paid professional, you need to account for your time—all of it. Post workflow hours don’t fall off trees. Your workflow boils down to a series of tradeoffs between quality and time—I think the term workaround is more appropriate. It’s a very personal choice that needs to fit within your skill level, schedule, budget, and worldview. If you have time and the budget and are being paid for your post-production time, then shooting flat and relying on color grading in post is the standard workflow. If video editing is your hobby, then a complex, time-consuming workflow probably adds to your enjoyment. If you’re new and dabbling in video with your DSLR, be careful about bogging yourself down with a workflow that might not be necessary for the level at which you are working. Your time is better spent honing your shooting skills and building your reel so you can get paying gigs doing what you intended to do—shoot great imagery.

So where does all that leave you for setting the Picture Style on a Canon or when choosing similar features on other HDSLRs? In the past I used to shoot neutral and then adjust the sharpness and contrast down a few clicks. However, after working with Snehal Patel, I learned that the Faithful picture setting is the closest I can get to a linear image file. The other picture styles add information to the image chain, whereas Faithful gives you what the chip sees without adding an adjustment curve or making any other visual changes.

The Faithful setting will give you a starting point to dial in your look. Don’t be afraid to experiment to find what gives you results that match your vision. Keep in mind that your goal should be to create a repeatable workflow chain that balances your image quality with your production and delivery times.

The Takeaway
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