Warning. If you’re not interested in disc authoring then pass on by.
TV around the world is divided up in incompatible regions. America has 30 frames per second (mangled to 29.97 because of the NTSC colour system). Civilised parts of the world use PAL at 25 frames a second. In film they still use 24 frames a second. In these three conflicting systems is a long tale of suffering.
When high definition came about there was some talk of unity but short lived. It’s not a simple matter to replace all the existing broadcast equipment, as well as providing a signal to the majority that still use their old TVs. Also the way lights blink in time with the power supply. TV will long remain PAL or NTSC. But in Blu-Ray discs there’s hope of a world standard.
It makes economic sense to make all Blu-Rays run at 24fps. Most of the media is drawn from film, so an exact match. You can also convert 30fps to 24 easily by a 3:2 weaving. PAL can be slowed down a bit so that the programme is longer, pitch correction will solve the music tuning so long as no one listens too closely.
That also suits animators nicely because a motion needs to be divided up, perhaps several times and 24 can split into 12, 6, 4, 3 and 2. The professional animators with whom I teach are used to these simple numbers and wince when I describe working with 12.5 frames. They’d be quite happy if everything ran at 24fps, and have their students think in film terms. The problem is that 24 can’t be broadcast without speeding it up – maybe that’s why Bugs Bunny is so frantic on local TV.
If you’re shooting video and then animating over the top locally you should use 25fps. Just about every camera is 25fps, and although some high end models are capable of a 24fps ‘film mode’ you can’t rely on it being there. Then you have the problem of televisions that run at 50fps, computer screens that run at 60fps and who knows what the next projector will do.
OK. So making up video for the Brisbane gig in 2005 I thought to use 60fps, matching the speed of the projector on offer. The theory was sound, the practice less so as 60 frames of high resolution animation was taking too long to render. After a while I dropped to 30 with motion blur, better for meeting the deadline. The idea of using an Xbox to replay the video didn’t work out, and the replacement laptop I bought looked absolutely terrible until just before the gig I realised that it was refreshing the screen at 59fps – some issue between Vista and my playback software. All was solved when I switched to 75fps. I think I was in rapture for about half a day until the penny dropped … at 75fps I could have just done the whole thing at 25fps. I’d wasted months, and created media that was no actual standard.
Now I’m rendering again in PAL. This means that all the older clips have had to be time stretched and that’s a complex business of synthesising 5 frames of video out of every 6. In most cases its working OK although there’s some strange tearing that has be repaired by hand.
Blu-Ray runs at set speeds – 24, 50 or 59.94. At 24 each frame is shown in full. At 50 or 59.94 it depends on the size of the image – at 720 dots each frame is shown for 1/50th of a second (in PAL) called “720p50”. At 1080 dots the image is interlaced into 2 fields each 540 dots tall and that is shown for 1/25th of a second, called “1080i25”. The only speed I can use in PAL is 50, showing each frame twice. Not too odd I guess as the shutter on a film projector shows each of the 24 frames twice. All this fussing does make one nostalgic for DVD.
You’ve got a choice of codecs. Originally Blu-Ray used the same MPEG-2 as DVD, just at a higher rate. With competition from HD-DVD, they added MPEG-4 and with some strong arming from Microsoft they added VC-1 which is SMPTE’s official ‘video codec number one’. If you’re on a Macintosh until recently you only had MPEG-2 as an option, the latest Final Cut Studio has finally cut it so you get MPEG-4 as well. I actually prefer VC-1 but damned if any affordable authoring software will allow this. Although MPEG-4 should look identical to MPEG-2 above a certain rate it always seems to be better. Compression times are hideous; you are looking at 3:1 on a fast machine, meaning you’ll need at least 3 hours to encode an hour show, and at least another hour to burn to disc. Do not leave to last day.
Next problem: when Blu-Ray was battling with HD-DVD the latter had an advantage – machinery that made recordable DVD could be upgraded to make recordable HD-DVD. Blu-Ray needed all new machines, until somebody worked out a way to use an organic dye that makes the process cheaper. It also makes it probable that the disc you burn won’t play in a different Blu-Ray deck. From painful experience – if the surface is blue (Panasonic), you’re probably OK. If it’s brown (Ritek) then you are going to have to check it in the playback machine. A PlayStation3 WILL play a write-once brown disc, but will vomit a rewritable brown disc. Figure that one out.
If you don’t have a Blu-Ray burner you can create a miniature version on a DVD. The DVD uses a fatter red laser so you are not getting the same data rate or duration. But I’ve managed to get around 45mins to an hour of good looking high definition on the cheaper disc. Through marketing and not logic the format is known as AVCHD Disc. That sounds like it’s related to the AVCHD format used on recent video cameras. Sort of, kind of. Yes they are both MPEG-4 streams but it’s not just a matter of copying files from your camera – the structure of the disc needs to be that of a Blu-ray.
And unless the Blu-ray player checks for this format it won’t play. A PlayStation3 will not accept an AVCHD disc as anything but raw files. If the player has the AVCHD logo on the case it may, it probably should, but don’t wager it. This is disappointing when DVD discs are a 16th of the price.
Right now Toast 10 is able to make AVCHD discs that work in many but not all players, SONY DVD Architect does not recognise the format, and Adobe Encore I am still testing. Other people have had good luck with Pinnacle software. You just have hang around the same forums you did when DVD first came out. Hell I was hanging around them when CD came out.
As they say in the magazines – this ain’t ready for prime time.