Reference and 'B' Frames

[_DW_]

I'm looking at the codec configuration in staxrip and I have a few questions. I'm on the first page looking at the reference frames and the b-frames. I'm thinking that a reference frame is a complete frame like a frame of film and a b-frame is the changes that happen in between reference frames. Is this correct?

The page currently says 8 reference frames to 16 b-frames. What is the ratio of ref frames to b-frames and to frame rate? Does this mean that I have 8 reference frames per second of video or 8 reference frames for the whole video?

An finally I remember reading that more than 5 ref frames doesn't do any better for live video. Is this correct? What about anime?

[Dark Shikari]

I'm looking at the codec configuration in staxrip and I have a few questions. I'm on the first page looking at the reference frames and the b-frames. I'm thinking that a reference frame is a complete frame like a frame of film and a b-frame is the changes that happen in between reference frames. Is this correct?No. Read the manual (http://ffmpeg.x264.googlepages.com/mapping), and if that isn't enough, try Wikipedia.

[_DW_]

Gee, thanks, I think. That really answered a lot of my questions. Looks like just about everything I thought I knew was wrong.

[cogman]

Gee, thanks, I think. That really answered a lot of my questions. Looks like just about everything I thought I knew was wrong.

Sorry, but without posting a huge post about what b-frames and reference frames are, Dark Shikari really couldn't tell you all that much. Pretty much all of your questions where based on a faulty assumption made in your first question, so answering them would be like answering a question of "Since the moon is made of cheese, how many mice could it support?"

However, the last statement you made, Yes, over 5 reference frames generally doesn't provide major quality gains. Anime receives some gains with more then five, however, they aren't THAT much.

[_DW_]

Sorry, but without posting a huge post about what b-frames and reference frames are, Dark Shikari really couldn't tell you all that much. .

Not a problem. I'm just going to assume the question I ask has possibly been ask a 100 or so times. I did look for the answers but didn't find what I was looking for. From what I read just setting the ref frames to 5 and the b-frames to 16 and not worrying about it, at this point, is the best way to go for now.

Which is pretty much what I've been doing.

[Selur]

b-frames 16 will be damn slow on encoding - when b-adapt is set to optimal, since it's not multithreaded atm. - so you probably want stick to 5 or less b-frames.

[JohannesL]

does a very high (like 10+) --b-frames actually help?

[Selur]

if it's used: yes, but for most sources x264 won't use more than 5 frames in a row to setting it higher than will only low the whole thing down.

[LoRd_MuldeR]

JohannesL, after your encode is done, look at the following line printed by x264:

x264 [info]: consecutive B-frames: 8.4% 52.2% 33.7% 2.8% 0.7% 0.8% 0.3% 0.0% 0.0% 0.4% 0.0% 0.0% 0.0% 0.6% 0.0% 0.0% 0.0%

That line will tell you how many consecutive b-frames were used actually.
The first number is no b-frame, the second number is one b-frame, the third number is two b-frames and so on.

As you can see, in this example x264 use 3 or even less b-frames in 97% of all cases, although I allowed up 16 b-frames!
Hence I could have used 3 b-frames instead of 16 b-frames and the result would have been no different.
Well, there would have been some difference, but that difference would have been negligible. And that is not an unusual example ;)

[anonova]

I've been using bframes 16 (with b-adapt 2) and ref 16 just to see if it'd ever use up to that many on some recent encodes. I finally saw 16 b-frames usage in a concert I tried. :P
x264 [info]: consecutive B-frames: 5.4% 26.1% 54.3% 8.4% 4.0% 1.2% 0.3% 0.1% 0.0% 0.0% 0.0% 0.0% 0.0% 0.0% 0.0% 0.0% 0.2%
Still probably wasn't worth the time though. *cough*almost 7 days*cough*

Since we're also talking about reference frames, could you also explain how to read the stats x264 gives at the end?
x264 [info]: ref P L0 59.6% 15.7% 7.2% 3.6% 2.7% 2.4% 2.0% 1.1% 1.0% 0.9% 0.8% 0.8% 0.6% 0.6% 0.6% 0.4%
x264 [info]: ref B L0 78.5% 10.5% 3.5% 1.7% 1.3% 1.1% 0.8% 0.5% 0.4% 0.4% 0.4% 0.3% 0.3% 0.3% 0.2%
x264 [info]: ref B L1 93.6% 6.4%
P frames use at least 1 reference frame? And what are the differences between L0 and L1 b refs?

[LoRd_MuldeR]

Still probably wasn't worth the time though. *cough*almost 7 days*cough*

In 98.2% of all cases 4 or less consecutive b-frames were used. For that video it's really not worth going higher than 4 b-frames...

P frames use at least 1 reference frame?

I think so. A frame without any references would be an I-Frame.

And what are the differences between L0 and L1 b refs?

Not 100% sure, but I think L0 and L1 distinguishes between "normal" b-frames (referring to i- or p-Frames) and b-frames that refer to b-frames (b-pyramid).

[Gabriel_Bouvigne]

And what are the differences between L0 and L1 b refs?
P frames can only use only a single reference list (L0), while B frames are using two reference lists (L0 and L1).
In the case of x264:
*L0 are previous frames, L1 are upcoming frames (considering display order)
*when not using b-pyramid, B frames are only using a single L1 frame.