B-Frames versus Reference frames. GOP size, Motion Vectors?

[InorganicMatter]

All right guys, I'm encoding for my PSP using Nero Recode. I'm targeting as low of a bitrate as I can get, while still looking decent at the native res of 480x272.

Some researching seems to show that the PSP can handle a combined total of three B/Reference Frames. So what should I do, 1 reference and 2 B's, or 2 references and 1 B?

Second: what's the Max GOP size, and what should I set it to for a low-bitrate (300kbps) situation?

And finally, what's a decent motion vector range: +/-128, +/-64, or +/-32?

I've learned a lot here doing this, and although these Nero Recodes don't look quite as good as my MeGUI ones, the convert times are twice the speed and the quality is still excellent. I might post a PSP Optimization guide once I figure all this out.

[akupenguin]

Some researching seems to show that the PSP can handle a combined total of three B/Reference Frames.
That's unlikely. There is a difference between using B-frames and not, and it does have some interaction with refs. But I can't think of any technical reason a decoder would support 1 B-frame but not support 100 B-frames.

what's the Max GOP size, and what should I set it to for a low-bitrate (300kbps) situation?

There is no maximum GOP size, and the bitrate does not affect the choice of optimal GOP size. The only factors that affect choice of GOP size are: the desired seeking precision, and the expected frequency of data corruption / transmission errors.

[InorganicMatter]

That's unlikely. There is a difference between using B-frames and not, and it does have some interaction with refs. But I can't think of any technical reason a decoder would support 1 B-frame but not support 100 B-frames.

All right, I guess that guy was wrong then.

There is no maximum GOP size, and the bitrate does not affect the choice of optimal GOP size. The only factors that affect choice of GOP size are: the desired seeking precision, and the expected frequency of data corruption / transmission errors.

Well, there's a box right here that says "Maximum GOP Size" and it defaults to 300. :confused:

[InorganicMatter]

Well, you were right, that guy was full of it. I just tried a film with 2 Reference frames and 20 B-Frames and it worked.

So how many of each do you suggest? I'm guessing that more frames means higher picture quality and longer convert time, right?

[drmpeg]

Well, you were right, that guy was full of it. I just tried a film with 2 Reference frames and 20 B-Frames and it worked.

Just FYI, the 3 B-frame limit is part of the Blu-ray specification. However, as you can see, it's not really a decoder limitation.

Ron

[Blue_MiSfit]

Well, that's true to a certain extent with reference frames. If you set 16 references, it will use that many, and will be horribly slow to encode. The point of diminishing returns is around 5-6 for most people.

B-Frames on the other hand are adaptive. In other words, if you say to use 20 b-frames, it won't most of the time. Usually, you see no more than 2 consecutive b-frames, maybe 3.

~MiSfit

[InorganicMatter]

All right, I ran some tests and it appears the PSP can handle a max of 2 reference frames. I'm thinking at this point to use 2 reference and 3 B frames?

[check]

The more complex the stream, the better the efficiency of the compression, and the greater the CPU power required to decode it. If you aren't worried about battery life, simply use the highest settings that work. If you are, you'll need to find a tradeoff yourself varying on what your personal weighting of these two factors is.

[audyovydeo]

There is no maximum GOP size, and the bitrate does not affect the choice of optimal GOP size. The only factors that affect choice of GOP size are: the desired seeking precision, and the expected frequency of data corruption / transmission errors.

Hello.

Can I take that to imply that max/min keyint are unrelated to profile/level compliance ? Even if I set, say, -I=1 -i=0 ??

audyovydeo

[Sagittaire]

Only really short GOP lenght will change the coder efficiency (for example max GOP lenght at 0.606 sec for HDDVD). 100, 200, 300 or more frame for max GOP lenght don't change really the coder efficiency. Moreover x264 will place Iframe for scene change and in practice the average Iframe interval will be always smaller than max key frame interval. For PSP you can use 120 frame for max interval and 1 frame for min interval (for example).