Hi Carl here for ProAV TV. So if you've been looking into any of Sony's recent
video cameras you have probably heard the XAVC codec mentioned. Some cameras have
XAVC-I, some have XAVC-S and some XAVC-L. Codecs can be one of the
most confusing items on that list of tech specs for your new camera. So as
Sony's codec is getting a lot of attention recently we thought we'd give
you a quick rundown of what each varient of XAVC is, and what that actually
means for you while your out there using the camera.
so first thing to understand the differences between the codec and a
wrapper. Wrappers are simply a container that holds together your audio and video
files as one file. They are the file extension you see on your computer for example a
quicktime's .MOV file or avi or mp4 . Each codec normally has a wrapper that it works well
with. And computer systems normally have a wrapper that they prefer, such as QuickTime on a
Mac, and AVI on a PC. now XAVC
prefers to use the MXF wrapper. So when you look at files recorded with the Sony
camera you'll see files with a .MXF extension and the exception to this is
the XAVC-S which prefers to use MP4's but we'll talk about that more
in a moment. So that's wrappers but XAVC is a codec. codec's are the way that the
camera compresses the information the sensor sends. It dictates exactly how
the image is stored and recorded so it directly impacts things like quality
compression artifacts noise how easily editing software can handle it
things like that. Its an incredibly important aspect of capturing video even if it is
a bit technical. Some popular codecs you might be familiar with are, AVCHD
very common codec recording 1080p in smaller file sizes. H.264 which is
still the standard for delivery across the board
websites like YouTube and Vimeo prefer H.264 as its possible to get very high
quality with low file sizes. it's not however ideal for editing, as its slow to
render and hard to grade, or prores 424 Apple's popular codec which is very
easy for extra software to handle it has large file sizes. Now some manufacturers
like Blackmagic and Atomos have actually started recording in prores
which is great it's a very high quality format but it does result in very large
files which will fill up your media very quickly
so to sum up the information comes off the Sensor the camera compresses the
video using a codec For example XAVC and then writes it to the media inside of a
file wrapper of some kind for example, .MXF
So XAVC was developed by Sony and released in 2012 along with their
high-end F5 and F55 cameras. while developing those cameras they decided
they needed a new family of codecs as existing options just wern't up to the
challenge of recording 4K resolutions. as we all know when you
start shooting in 4K, you end up with four times the information of 1080p
that means you need four times the data rate, and four times the processing power
which is a big challenge for camera manufacturers and previous codecs just
couldn't handle it
Sony arent unique here each manufacturer has its own solutions to the problem for
example Canon have their own new codec XFAVC which achieves the same thing
in a slightly different way. So XAVC comes in three different flavors, I L & S
they are similar but different in many ways so let's have a quick look at each of them.
So XAVC-I is basically the main full quality option in the family
sony's higher end cameras like the F5 and F55 use it, and it was one of
the main reasons that the cheaper FS7 was so popular when it came out.
The I at the end
stands for intra-frame. Which is the most important difference between this
and XAVC-L and S. An intra-frame codec records each of the frames of your video
in its entirety. each frame contains information about every pixel in the
image and this means that you get the maximum quality and less chance of
compression artifacts. it also means it's much quicker for editing software to handle
as each frame exists by itself and doesn't rely on the frames before and after
it for information. an implication of this is that when you're grading and applying
effects you would have less chance of seeing issues and artifacts in your
image as the codec is much easier for the computer to process. so XAVC-I
has no real limit on color information. it can record up to 12 bit 444 color and it
can use data rates up to a whopping 960 megabits a second. no
camera can actually record as high as that yet. the highest quality you'll get at
the moment is six hundred megabytes a second 10 bit 422 with the high-end F55. so it
takes up more space but it is a higher quality image with less artifact issues
and it's easier for your computer to handle. so why doesn't every camera use it? well
because it's expensive. the cameras need much more processing power and more
expensive media which can handle the high data rates so cameras tend to be
larger to make room for the processors and accompanying heatsinks, so if you're
looking for a small light camera, with cheap media, chances are it won't be able to
handle XAVC-I.
so if your camera can't handle XAVC-I what's the next best thing? XAVC-L can
still handle all that important color information up to 12 bit 444, though
it gives you smaller file sizes which can be recorded to cheaper media. for
example Sony recently released the FS5, a small and light 4k video
camera which records to cheap SDXC cards and is able to do this because it
records its data using XAVC-L instead of XAVC-I. so what's the difference?
well the L in XAVC-L stands for long-GOP compression. this is a way of
reducing the amount of data we need to record while keeping the quality as
high as possible. while intra-frame codecs like the XAVC-I we just talked about
treat each frame individually, long-GOP codecs do it very differently. say you were filming a
shot from a tripod of a person walking along a the street. in the first frame, the
camera will obviously have to record everything. But in the second frame things
get clever. the camera looks at the difference between the frames and only
records new information if bits have changed. for example the parked cars
won't have moved at all, so the camera doesn't need to record that information
again this is already there in the first frame. instead it can only capture the
items that have moved like the person walking and the trees swaying in the wind
this means that the camera has to record significantly less data in each
frame is its only recording the changes which saves lots of space and processing
power. so if you looked at the same clip recorded in each codec the difference in
quality should be minimal but there are several drawbacks to XAVC-L. firstly
long-GOP compression works great in an ideal situation. but what happens if
you're shot isn't perfect? what if imperfections like high ISO and fast
movement confuse the compression methods
well you end up with artifacts, image smearing, aliasing, things like that
which you don't want in your image. Secondly, long-GOP files are much harder
for editing software to handle. all editing software does fully support it
its just the nature of the codec requires more work for the computer to process. if
you imagine your video file as a series of frames recorded in Long-GOP, so the first
frame contains all of the information then each sequential frame contains only
the changes. if you open that clip in your editing software and go to halfway
through the clip, the software can't just show you the frame you selected
because its an incomplete image, so it's got to search back through the previous frames until
it finds everything that is looking for.
so each time you move that play head to a different part of your video, it has to do
the same process, searching the frames around the one is trying to show you
and piecing together all of the information until end up with a preview image that
it can show you. so luckily modern editing software is very powerful and it can
handle tasks like this incredibly well. but no matter how powerful the computer
and software it will still be slower to edit and render than an intra-frame codec
like XAVC-I. so to summarize with XAVC-L we get very clever compression
methods that drastically reduce file sizes at minimal loss of picture quality
but there's a slightly higher chance unwanted artifacts and editing the
footage will put more pressure on your computer.
Now XAVC-S is what Sony refer to as the consumer option in the XAVC Family
it is limited to 8bit 420 color and it records to an MP4 wrapper instead
of MXF files like the other two options. now this is a codec designed to have as
many of the advantasges of using XAVC as possible while keeping it easy and
simple to use for consumers. Sony presumably chose mp4 files because
they're easier to use. They playback easier outside of editing software, and they have a
simpler file structure than MXF. so XAVC-S is a long-GOP Codec, just like
XAVC-L, but it has a maximum data rate of 100 megabytes per second compared to
XAVC-L's maximum of 760 megabytes a second. that means you're gonna
get much smaller file sizes but much more compressed video all of Sony's a7
range of mirrorless cameras like the a7s and a7r use XAVC-S but
it is worth mentioning though even though XAVC-L has a maximum of 12bit 444
color and 760 megabytes of data no cameras exist that actually shoot that with
it, its just a hypothetical limit of the technology interestingly at the moment
XAVCS actually works better in most editing software
than XAVC-L does, even though they are both long-GOP codecs. this is simply
because XAVC-S is more widely used and so the developers of the software spent
more time on support for it. it's still a long-GOP codec you won't be able to get
around that. but I find my software does handle it better than XAVC-L although
that may well change over time. so we have long-gop compression and really
small file sizes so you might assume that any camera recording in XAVCS
will have bad looking video
well luckily that's not true at all. Sony have managed to squeeze a lot of quality
into this small codec and the majority of the time you wouldn't even notice a
difference between this and
XAVC-L. this is a great codec which strikes a nice balance between being easy to use
and recording great-looking video. so hopefully that helps with some of the
confusion between different flavors of XAVC in Sony cameras. talking about
codecs can get a bit heavy but it's important to know the differences when
you're choosing between these cameras as each codec comes with its own
implications & difficulties. if you have any questions about anything in this
video or maybe you think we've missed something important to talk about. just leave a
comment below and I'll try my best to get back to you. this sort of video is
something a bit different for us so if you enjoyed it and found it useful
please do let us know, and we will try and make more.