If you’re taking your video production seriously then it’s crucial to understand what codecs are all about and the ones that are right for you. CVP expert Jake Ratcliffe explains more.
HOWEVER EXPERIENCED you might be as a professional photographer there is still a lot to get your head around once you really start to take video production more seriously. One of the terms you’ll encounter early on, which you won’t have come across when shooting stills, is codecs. You’ll soon discover that there are quite a lot of these to consider and they all offer something slightly different.
So, what are codecs all about and which ones might best suit your approach? To basics first, and the name has been arrived at through the meshing of two words, namely coder and decoder (co/dec). In simple terms video files are so huge that it would be really difficult and time consuming to work with them in their original
Your codec will come in a container, which is like a wrapping that refers to the way that information is stored, but not how it’s coded. The container is used to combine everything into one file as well as to store metadata, and there are many different formats, some of the ones commonly used being MP4, MOV, AVI and MXF.
“When recording a video and audio file the format of your file is defined in three parts,” explains CVP expert Jake Ratcliffe. “The audio and video codec and the media container format that’s being used. The codec portion of this is the software that’s compressing the video you’re recording. Compression is really complex, so if you really want to learn more then it’s worth a trip online to do some browsing. However, without getting into the full details, the main point to be aware of when working with codecs is how different compression can affect your image and file size.
“When you compress an image you inevitably lose data and, as a result, you’ll have smaller file sizes. When closer to lossless compression you’ll have more data, but your file size will have increased. What codec you eventually choose to work with will depend on your needs.” “When you compress an image you inevitably lose data and, as a result, you’ll have smaller file sizes. When closer to lossless compression you’ll have more data, but your file size will have increased. What codec you eventually choose to work with will depend on your needs.”
Jake sees the perfect example of the choices that need to be made contained within the feature set of the recently launched Sony a7S Mark III. “With this camera you have the option to shoot in both XAVC S-I and XAVC S codecs,” he says. “So, what’s the difference? Simply, XAVC S-I uses intraframe compression, whereas XAVC-S uses inter-frame, or Long-Gop, compression. Intra-frame compression happens on a frame-by-frame basis, whereas inter-frame takes place across multiple frames, only keeping the information that changes from frame to frame. Accordingly, the intraframe compression will result in larger file sizes but more data, while inter-frame will have smaller file sizes but less data.”
XAVC S is the standard codec that’s been used on Sony mirrorless cameras going back to the original a7S, and the use of H.264 compression ensures lean data rates and an end result that plays well on a computer. On the downside its Long-GOP codec means it’s more difficult to edit without transcoding, since colour information is stored across multiple frames.
The XAVC S-I codec is new to the Mark III and it also uses H.264 compression, but because of intra-frame compression each frame contains the full amount of colour information and will be easier to playback and edit. However, because the data rates for this codec are much higher it will require faster media and more storage space. It shouldn’t require transcoding, however, and this is likely to make it the most popular codec on the a7S III for documentary and broadcast shooting.
The third codec to be found on the a7S III is XAVC HS. This is also a fresh addition to the model but, unlike the other two codecs, it uses the newer, more efficient H.265 compression standard, and this is capable of providing higher quality with smaller file sizes. “Our industry is constantly evolving and everything moves in relation to each other,” Jake observes. “We’re seeing H.265 finally starting to receive wider use as computers are finally being fitted with the necessary decoders, but H.266 is already round the corner. With resolution also increasing with the likes of 8K video becoming more widespread, more efficient compression is going to be a key part of delivering content going forward.”
So, on a single state-of-the-art modern hybrid camera you can see three options being offered, each one of which will deliver a different end result. If you understand codecs and what each has to offer you as a user, it makes the selection of the right camera to invest in easier and, as always, retailers such as CVP have experts on hand who will be happy to walk you through any potential minefields.
The Numbers Game
When you’re looking around for your next video-enabled camera you also need to be aware of the numbers that might be associated with a particular
model. For example, what exactly is meant by 8-bit and 10-bit and what’s the difference between 4:2:0 and 4:2:2 Chroma Formats? More importantly, will choosing one over the other have a big influence on the ultimate quality of the footage you produce?
“Whenever you’re considering the formats the camera can shoot you’ll come across this set of numbers after the resolution and frame rate that are offered,” says Jake. “They can be quite important: the 8-bit or 10-bit part is referring to the bit depth of the image being recorded, so essentially it’s telling you the amount of colour that can be stored in an image. If your camera can only handle 8-bit then it has a possible maximum value of 256 for each channel, which will give you roughly 16.7 million colours, whereas 10-bit has apossible maximum value of 1024 for each channel, which will give you just over one billion colours. This is clearly a huge increase and will give more information.
“Because you’re capturing much more colour it not only means you’ve got more data to play with in post-production, but it also means you don’t run into common issues, such as banding with 8-bit when really pushing your grade.
“Meanwhile the 4:2:2 number is telling you the chroma subsampling, which is a compression type being applied to the image to allow more luma information to be present in the same file size. The ratio that’s listed with the video format is the ratio between how often the chroma and luma values are sent: if you’re working with 4:4:4 it means that there is no chroma subsampling, while 4:2:2 means that for every horizontal line where four luma values are scanned there are two chroma values, while with 4:2:0 there are none. Essentially the higher numbers indicate less compression, which means better colour and less of the artifacts that can occur when using chroma subsampling.”
Staying on the subject of compression, the use of a proxy codec, such as ProRes or DNX, will give you a smaller copy of your high-resolution RAW footage, so that you have a much smaller file to work on during your editing process.
“Working with proxies can be a really great option to speed up your workflow,” says Jake. “ProRes and DNX have been two of the primary working formats for years, with ProRes being optimised for OSX and Final Cut and DNX for Avid. However, lots of mirrorless cameras will not offer these in-camera: instead, it will normally be a proxy version of their normal internal codecs. This is where shooting with an external recorder such as the Atomos Ninja V (CVP price £630), could be a good option if you want to work with ProRes or DNX, or the post-production workflow you’re working with requires it.
“Atomos has been leading the way with external recorders for years now and they are fantastic at combining great monitoring functions with versatile recording options in a range of formats. With the Ninja V, for example, this is not only a high quality bright 5in monitor but it also allows you to record in DNX, ProRes and ProRes RAW, all of which are excellent formats to work in, and you’ll often achieve better results than you would with the internal options in your own camera. However, if Resolve is a key part of your workflow then Blackmagic’s external recorders are also a good option. You just need to make sure your camera can output Blackmagic RAW (BRAW).”
Compressed RAW codecs enable filmmakers to get the benefits of retaining all the information in their files but with much more manageable data rates than uncompressed formats, such as Cinema DNG. Apple has worked with both Blackmagic and Atomos to create ProRes RAW and BRAW, which are two of the most popular formats in the market at the moment. Both are excellent options and which one you decide to use will inevitably come down to your chosen workflow.
Yet again your choice of camera could well affect which route you go down, since models that are optimised to use ProRes RAW will produce files that can’t be edited in Resolve, while Blackmagic cameras using the BRAW format will output files that can’t then be edited in Final Cut Pro X.
“It will affect your workflow choices,” says Jake, “but if you work with an editor such as Premiere Pro then you can now use both BRAW and ProRes RAW, though you will require the relevant plugins from both the Apple and Blackmagic websites before getting into your edit.”
For those fresh to high-end video, it can all seem technical and a lot to take in at first but as you start to acquire fresh skills it will all very quickly start to make sense. Working with a trusted partner to ensure you make the right equipment choice at the outset is crucial though, and will save you making a wasted investment. Evolving technology might be ensuring that the goalposts will continue to change all the time, but you still want to be as future proofed as possible and able to take advantage of the most efficient workflow that’s available.
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