Wired

Or “How NOT to do HD encoding.”

I am sure you have noticed the push to make consumer camcorders HD. It seems like every month the big manufacturers are releasing new HD camcorders at lower and lower prices. So what is up with these HD cameras and are they any good?

According to the reviews I have read, the HD push in the consumer space is only to sell more product, and thus make more money. Of course. But the quality of these HD cameras is really pathetic. The only thing HD about them is the recorded resolution, which just has to be 720 horiz pixels or more. It says nothing about how good the images look.

So what went wrong? Well the compression is what went wrong. Let’s think about this a bit. You take 4x as many pixels to make HD, then you compress it to fit into less space than regular standard definition (SD) takes, and you expect it to look good? No way! It’s NOT going to happen.

I am not saying that the new codecs, AVC-HD in particular, are terrible. They are quite good at compressing video. BUT, not in realtime. When you take a video and compress it via multi-pass compression using AVC-HD, the results can look really good at low datarates. BUT, when you compress directly in a camcorder, you DO NOT have the time to do multipass encoding. Therefore you must encode in realtime. And if you know anything about realtime encoding, you will know that it’s a big compromise when encoding the video. You just do not know anything about what is coming up several frames later, therefore you make guesses and the results are a big big compromise in quality.

Now I have seen AVC encoded HD look outstanding at very low bitrates, but the compressors took 1 week to encode 10 minutes of video. Sure that’s completely impractical, but damn the results were good. But if you have to do realtime encoding, like in a camcorder, your results will be atrocious. You just can’t guess properly to make an effective realtime encoding of HD at low datarates.

So what’s the answer? The answer is to NOT use AVC-HD or MPEG4 for capturing your HD content. Use the highest bitrate you can for your capture. HDCAM is best, but not everyone can afford the 250K for the camera. I have seen pretty good results from HDV, which records at 25mb/s. For comparison, AVC-HD is encoding to around 11mb/s. Way too low for realtime AVC encoding.

So look around the net for some reviews. You’ll see what I mean. These new consumer HD camcorders are a big stain on the HD marketplace and I hope they die a quick death before they turn the public off of HD recording.

-Mark

mark @ wiredinc . com

This entry was posted on Tuesday, February 26th, 2008 at 10:39 pm and is filed under Marks Corner Table. You can leave a response, or trackback from your own site.