Sony XAVC codec explained

Sony will release a new H.264-based codec this month to enable its equipment cope with resolutions beyond HD, as well as higher frame rates, while delivering higher quality pictures. It looks likely to be Sony’s new core codec, so it could play an important role in future productions.

Once Sony’s new PMW-F5 and PMW-F55 4K cameras start shipping (sometime before BVE), users will be able to take advantage of the new, more efficient, mid-range XAVC codec, which has been designed for 4K, and will offer both intra frame and the more efficient Long GoP encoding. It will also allow higher framerate recording at 1080p.

Sony is offering the F5 and F55 as multi-format cameras, rather than just XAVC, “so that they would fit within the workflow people want rather than restricting choice,” said Product Specialist Sebastian Leske.

The cameras will support four codecs: XAVC, for high frame rates and 4K; MPEG2 at 50Mbps; MPEG4 SStP (Sony’s SR Master codec); and Raw 4K, “by the switch of a button, depending on what job you want to do,” added Olivier Bovis, Sony’s Head of AV Media.

XAVC is an extension of H.264 (AVC/MPEG4), using the highest Level 5.2 of the standard, so it is very solid in terms of multi-generational support, he explained.

However, as Sony already had HDCAM SR and Raw on offer, why did it need yet another codec?

“The data rate from an F65 sensor can be as much as 35Gbps, whereas the new SxS Pro+ cards can go up to 1.3Gbps. So, we still need efficient compression to take all that data and package it in a manageable way,” explained Strategic Marketing Manager Peter Sykes. Besides, MPEG2 simply couldn’t cope with 4K, whereas XAVC is not only able to handle higher resolution but higher frame rates too.

He doesn’t believe that Raw is suitable for every-day production as it results in much higher data rates and can't be used as an interchangeable format. Although Raw offers all the flexibility some productions may need for high-end postproduction, it is inextricably linked to the camera sensor, which complicates the workflow and makes it less suited to productions that need to use a variety of different cameras.

Multiple formats

The F5 and F55 can record existing XDCAM HD formats at 50Mbps or 35Mbps, HDCAM SR (MPEG4 SStp) at up to 220Mbps or XAVC at 440Mbps. For 4K work, you’ll be able to use intra-frame XAVC at 10-bit 4:2:2, which will require 240Mbps at 24p or 600Mbps at 60p. For HD, it will record 10-bit 4:2:2, at up to 60p, at 200Mbps. It can also deliver proxy 4:2:0 images at low bit rates. Users will be able to choose between 8- and 10-bit recording for both XAVC and MPEG2.

XAVC uses an MXF wrapper, as it is “industry standard and well recognised,” said Sykes, and its implementation is identical to Sony’s MPEG2 and MPEG4 SStP MXF OP-1a files.

“It is an enabling technology for a range of products that will emerge from now on,” he added. “It’s a major part of our plan for our acquisition products. XAVC will become the core codec for applications beyond HD and for higher frame rates.”

“To drive beyond HD we had to develop XAVC,” agreed Leske. “The design is future ready.” It will be able to do 4:4:4 (where it will be able to go up to 1.2Gbps), although the F5 and F55 will use HDCAM SR for 4:4:4 work.

“To go beyond HD we needed a new codec, but it is also useful for 1080 50p and 60p,” he added. “It uses a different mechanism to keep the highest quality we can. It allocates more bits to the details (like hair) than for flat areas (like a wall).”

It uses “a pre-coding mechanism to maximise the picture quality,” expanded Sykes.

This uses bit estimation, the same procedure as used for DVD authoring, which estimates what bit rate you need to get the highest quality. If it doesn’t reach it, it does it again. Used as an intra-frame codec, XAVC will do this for each frame, so they are all recorded to the highest possible quality.

At present, H.264 codecs set the parameters for a recording when you start recording, and stick to them, whereas XAVC can change them every frame, so that when you shout ‘Action’, and there is suddenly lots of movement and fine detail in the shot, you aren’t limited to parameters set when nothing was happening.

Sykes believes that 4:2:2 10-bit XAVC at 100Mbps “will be a good basis for broadcast infrastructure and relatively easy to handle.”

Open season

XAVC has been developed as an open format, providing a license program for other manufacturers in the broadcast and production industry to develop their own high quality and high frame rate products.

“It is a codec we are going to be using for lots of different applications,” said Sykes. Sony developed the low power consumption chipset used in the cameras. This not only does XAVC, but also processes MPEG2 – and because it is so fast can do both at once, so that the F55 can record both 4K XAVC and XDCAM HD at 50Mbps simultaneously to its SxS Pro+ card.

Currently, it seems that the XAVC workflow will be supported by such manufacturers as: Adobe (CS6 with Rovi Total Code Plug-in installed), Apple [[UPDATE - Sony XAVC plug-in for Final Cut Pro X (version 10.0.8) now available to download]], Avid, Grass Valley, Quantel and Sony (Vegas Pro 12) for non-linear editing; Assimilate, Codex, Colorfront, FilmLight, MTI and YoYotta for on-set dailies; Assimilate, FilmLight and Quantel for colour grading; Rovi for software codec management; and Matrox for a codec board.

The F5 is designed for HD on-board recording, requiring an external recorder for 4K, whereas the F55 can record 4K internally as well as HD.

On-board recording, in whatever format, will typically require about 25 Watts, but adding the external Raw recorder will add an extra 22W. With the viewfinder attached the complete camera will require about 50W, which is good for a 4K camera recording Raw.

For 16-bit 4K Raw, the system runs at data rates of up to 2.4Gbps for 60p, but this will only be possible with the new Sony AXS-R5 recorder, which fits to the camera body with no need for cabling. The cameras will be able to record both Raw externally and XAVC internally at the same time.

PMW-1000 Deck

To support XAVC (and SxS recording in general), Sony has just announced the new PMW-1000 Memory Recording Deck. This is a half-rack sized recorder, with two SxS memory card slots and VTR-like jog/shuttle operations, that is suitable for both studio and Outside Broadcast use – and is the first stand-alone recorder to handle the new codec.

Following the launch of the PMW-F5 and PMW-F55 CineAlta cameras, “the PMW-1000 studio recording deck is the next natural step to bring enhanced and easy workflow support,” said Fabien Pisano, Strategic Marketing Manager, Sony Europe. “The versatility of the PMW-1000 in terms of interfaces, coupled with linear-like operation and the ability to record the XAVC HD format on SxS media, make it an ideal choice for broadcasters and production houses looking for an affordable, quality production solution or for a smooth transition from SD to HD.”

PMW-1000 users can select recording and playback formats from HD (XAVC, MPEG HD422 and MPEG HD420 50/35/25Mbps) and SD (MPEG IMX 50/40/30Mbps and DVCAM 25Mbps) in a variety of frame rated. For anyone who still has to do some work in SD (are there many?) the recorder is designed to make the transition to HD easier, and can also do up-and-down conversion from/to HD.

The PMW-1000 offers a wide range of AV and IT interfaces including: HD-SDI, SD-SDI, HDMI, and composite outputs. An RS-422 interface enables it to be used as a feeder for linear editing while a Gigabit Ethernet (1000BASE-T) port allows for high-speed file transfer in network or non-linear operations. The PMW-1000 also includes a HDMI output at the rear for easy monitoring on HD displays. 

A USB interface on the front panel enables easy connection of external USB HDDs without a PC for the direct copying of clips.

It also boasts three-way power source selection. It can operate on AC, DC or battery power, and so it can even be used on location. It should be available in Europe from April.

Procam order

The 4K cameras seem to be attracting a lot of interest. One of the UK’s biggest broadcast hire facilities, Procam TV, has just spent £500,000 on the PMW-F5 and PMW-F55. Procam believes it is the largest single transaction of its kind in the broadcast hire industry.

It is getting its first instalment of 12 cameras this month, and expects considerable demand from its current customers as well as attracting new clients.

By David Fox