|MPEG-2 and Television
||[Nov. 10th, 2005|11:07 am]
|||||U2 - City of Blinding Lights||]|
The new TV standard uses MPEG-2 to compress video. I think this is going to have serious negative effects upon cinematography.
MPEG as most of you know does inter-frame compression and works best when two adjacent pictures in the video are similar. On a static image with lots of detail, the detail becomes crystal-clear immediately. By contrast, if there's lots of stuff happening dynamically in the video, the compression loses so badly that the blocks in the video become visually apparent - MPEG subdivides the picture into individual coding blocks, and when there's a lot going on, about all the encoder can do is to tell you what each block's color and brightness should be.
So what does this do to cinematography?
Well, I've seen horrific shows like Boohbah (a kids show which is roughly Tellytubbies on a bad acid trip, which is really saying something when you consider that Tellytubbies is pretty weird to start with). Being a kids show, there are segments where an actor and a few props are messing about in the frame. And to calm things down for preschoolers, the frame is outdoors with scenery, with a fixed camera position and zoom, and few scene cuts.
This works fabulously in HDTV. The scenery, which was pretty to start with, is just amazing. You see incredible details in the trees, beach, plants, desert, or whatever in the background. And with just the actor and props moving about there's plenty of bits available for coding all that nicely enough.
I've also seen stuff like a darkened room in a lightning storm kinds of shots. Since MPEG doesn't have a way of coding "change the DC brightness by X", when the lightning flashes you are treated to a room full of blocks. Oh yeah, that looks sooo good. Same thing happens for explosions where the brightness changes dramatically -- it just looks blocky.
The principle here is a bit more broad than just simple brightness explosions and flashy lights. The Smallville title sequence (ya know, the part with the theme song and all that) now has meteors flying about, fast cuts, multiple video sequences being layered into different locations on screen simultaneously, and all that. It looks bad. Really bad. The first meteor comes in, and as it gets close it becomes too large and dynamic, and turns to blocks.
DVDs don't have this problem so bad because their bandwidth is more dynamic. If they need more bits for a lightning storm sequence, they can steal those bits from some softer part of the movie. Because HDTV is broadcast over a bitrate-limited medium, they can only steal bits from the few seconds surrounding the bit-intensive scene.
So the future? If HDTV really becomes predominant as I expect, I'd bet cinematography and editing will change. Fewer scene changes. More static shots so you can see the background. Say goodbye to the use of darkened rooms with flashy lights in Halloween screamfests.