09 Aug 2015

Ten reasons to like Sony's pro video format, XAVC

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Ten things to like about XAVC Ten things to like about XAVC Sony/RedShark


RedShark Summer Replay: Sony's XAVC is used across an increasing number of its professional camcorders. Why did they choose yet another format? There were good reasons, as we explain below.

You could hear the groans from experienced camera operators and post production experts as Sony announced a new video format in October 2012, on the day that the F5 and F55 cameras, which use the new format, were revealed.

It was understandable. Very few professionals wake up in the morning wishing that there was yet another video format to grapple with.

But progress is so rapid in the professional video industry that it’s impossible to stand still for long. If we did, we’d all still be using Digital Betacam. The simple fact is that 4K wasn’t covered well by existing formats. Something new was needed to improve quality and usability at the same time as keeping video bitrates (and storage requirements) to a minimum. Here’s just one example: existing H.264-based codecs can’t handle 1080 50p/60p encoding - a format that’s increasingly used in modern productions.

A few industry observers commented that the new format might just be an attempt by Sony to make its cameras proprietary. Every company wants to make customers buy its own products, but, having spent time talking in detail to Sony about the XAVC format, it’s clear to me that this is a genuine technical advance that gives real benefits to users, which is flexible enough to be current for some time ahead.

Since the F5 and F55 were launched, most NLEs have provided native support for the new format, and it has also spread to much of Sony’s new camera range.

Just a bit of background to put all of this into context:

XAVC is based on H.264, but the idea that H.264 is a single, standardised codec is not really true at the practical level. There are dozens of tweaks and optimisations - and fundamentally different parameters - that can be set to suit a camera or the way it is used, and this is the background to the reason why Sony decided to develop their own set of codecs, called XAVC.

You can think of H.264 as a set of building blocks; a toolkit, if you like, that Sony has used to create their XAVC ecosystem. They’ve tweaked the algorithms, made it more efficient, and they’ve added a pre-processor that conditions the video before the encoding process. All of which means that when stacked up against other codecs, it is typically more efficient, and easier to use in post production. What’s more, XAVC has been built using the latest generation of encoding technology, 5.2, ensuring that it is even more efficient.

1. It covers a very wide range of bitrates

It has to. Over the last few years, the ability to get data off a sensor has mushroomed. 4K video requires a sensor with 8 megapixels, and sensors with this resolution have been around for at least ten years, but it is only recently that we’ve been able to get the data off them quickly enough to create video with it. Remember that Full HD is only around 2.5 megapixels, so 4K calls for a 4x increase in raw (ie uncompressed) data rates and storage.

XAVC is designed to scale from 15 mbit/s to 960 mbit/s. This covers just about every likely frame rate (except ultra slow motion) and includes HD as well as 4K.

2. It is designed for acquisition as well as post production

Previous versions of H.264 have been designed primarily for distribution and not for capturing video. This has led to inefficiencies and difficulties with scaling for higher bitrates. For example, the type of H.264 that was designed for Blu Ray and for satellite transmission was never going to be ideal for cameras. By going back to the basic building blocks of the format, Sony has been able to make a codec that is equally happy in a camera and in post production and which brings tangible benefits to both. This is much better than with previous generations of H.264-based codecs which were arguably not optimal for use at the front end of production.

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David Shapton

David is the Editor In Chief of RedShark Publications. He's been a professional columnist and author since 1998, when he started writing for the European Music Technology magazine Sound on Sound. David has worked with professional digital audio and video for the last 25 years.

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