Blu-ray 3D for sport?

We were intrigued when we spotted in JB Hi Fi a new Blu-ray 3D title. It was a footy match. Not just any match, it was the exciting draw in the Australian Football League Grand Final of 2010. Called 2010 AFL Grand Final Draw 3D, it had been released by Australia’s own Visual Entertainment Group.

The government had granted a trial licence for the broadcast of several sporting events during that year. That had included some of the Soccer World Cup matches, broadcast from South Africa, and the Rugby League State of Origin matches.

And the AFL Grand Final. Which was destined to end in a rare draw. A new game was conducted the following week and that one yielded a result, but because of its quite unexpected need, not only was it not shot in 3D, it wasn’t even shot in HD!

Obviously the 3D almost-conclusion to the 2010 season appearing on Blu-ray was welcome, but how could it be presented in Blu-ray 3D?

There is a basic problem with Blu-ray 3D for this purpose: it has the wrong frame rate. This format works, like the cinema, at 24 frames per second. That is, the video consists of still pictures shown in sequence at a rate of 24fps.

But Aussie TV works at 50 frames per second. Somehow downconverting this to 24fps would involve tossing away lots and lots of picture information. If nothing else, it would be harder to follow the ball because more than half the frames that made up the action would be lost.w

Happily the company behind the disc hadn’t been formally precise when labelling the disc ‘Blu-ray 3D’. In fact it was in the same format as the 3D TV broadcast. That is, the left and right eye views were presented side-by-side in single frames at the full 50 fps. You have to set your 3D TV to side-by-side 3D decoding mode to enjoy it (incidentally, unlike Blu-ray 3D, this disc isn’t compatible with a 2D only system).

We said ‘the same format as the 3D TV broadcast’, which is more or less true. But there was one difference. The broadcast would have been with a video bitrate of around 10 to 12 megabits per second. A regular Blu-ray movie achieves higher quality employing more data, typically around 20 to 25Mbps, and in some cases up above 30Mbps. Which is what this disc offered: 32 megabits per second, ensuring that the picture quality was about as high as is possible. It certainly looks excellent.

And it carries a moral: Blu-ray 3D is a format that’s great for entertaining movies. But when it comes to sport, where you need to be able to track that ball moving at high speed across the frame, sticking with 50 frames per second in the side-by-side format (which results in half the horizontal resolution being lost) is well worth it, rather than trying some heroic effort to stuff these 50 frames somehow into only 24.