What does RDO Bframes and Bidirectional ME do?

[JarrettH]

What do these options do?

When I disable them the 2nd-pass encoding time decreases by 3-4hrs!!:scared:

Do they contribute significantly to the image quality? Maybe I misunderstand, but it sounds like these options increase efficiency which in my mind sounds like compresses better. If there actually is an increase in bitrate (like with mixed ref) is it anything worth the added time? I'd like to get a feel for when these added options would be applicable and what they do in simple terms :)

Using HQ-Slow and Soulhunter V2

[Dayvon]

They have to do with motion detection. So they won't get you a smaller file size, but they will more effectively use the bitrate that you have set. In other words your quality will be better.

As to whether or not you should use them, that depends on if you want the time sacrificed to get better quality at a certain size. The project I'm working on now, I'm using it because the video quality is a big deal to me with this backup, and I really need to hit a specific size. Many other backups, I don't use the RDO Subpixel because that extra bit doesn't matter 'cause I just used a higher bitrate instead because file size wasn't an issue.

[JarrettH]

I have a feeling one or the other setting is increasing my file size. Sure are right about that! So could something at 800kbps with both options enabled be comparable or better than the same clip at 900kbps with them disabled?

Edit* since MeGUI 0.2.3.2055 the bitrate calculator has been fixed!

[foxyshadis]

Quality options don't automatically map to lower size in "constant quality" modes, either cq or crf, because they're more complex in how they modify the encoding process and interact with rate control. They won't even always make every frame look better, as long as it increases the overall quality (and in a few cases, particularly very noisy or jerky video, where advanced options can hurt). I'm not an expert, but Akupenguin knows the specifics if you really must know about the internals.

In bitrate mode the end size should never change, just the overall quality.

[Dayvon]

I have a feeling one or the other setting is increasing my file size.
Nope, the only thing that should increase or decrease file size would be the frame rate, or type of frames (b-frames). These options do neither.

So could something at 800kbps with both options enabled be comparable or better than the same clip at 900kbps with them disabled?
That might be a good way of looking at it. But maybe more like 800kbps compared to 850kbps. But you have to realize these options will help on specific problem scenes the most. Not the entire movies overall quality.

[JarrettH]

Now I must ask...

Do you think using Multi-Hex + higher bitrate would be more optimal?

:D

[foxyshadis]

Multi-hex is always better than hex. Higher bitrate is always better than lower. There's no yes or no answer, since that depends on your source and how much extra time and space you're willing to spend.

[JarrettH]

I think I can say without a doubt now that RDO for bframes slows it down by the 3hrs. I disabled RDO for Bframes, used multi-hex and it still only took 9hrs for this 106min movie versus the 11-12hrs before. Of course now I'm wondering whether multi-hex or RDO for b-frames would be better. Hehe

First test (11hrs):

800kbps
Hex
No Fast Pskip: enable
RDO Bframes: enable
Bi ME: enable
5 Mixed Ref
Soul V2 and Flat 16

Second test:

800kbps
Multi Hex
No Fast Pskip: enable
RDO Bframes: enable
Bi ME: enable
5 Mixed Ref
Soul V2 and Flat 16

Third test:

800kbps
Multi Hex
No Fast Pskip: enable
RDO Bframes: disable
Bi ME: enable
5 Mixed Ref
Soul V2 and Flat 16


I think that should pretty much narrow it down for me speed vs quality wise. This is for a slow motion 106min movie - Broken Flowers. I know some of the options are more suited for high motion, but I'm trying to fit the best quality/reasonable time on 1CD. I don't mind up to 10hrs, I'm seeing how far I can stretch the HQ-SLOW profile

[Dayvon]

You might find that having "no fast p-skip" button checked will slow you down quite a bit. I've been running encodes without this, and not been experiencing to much blocking. Then again, I've normally been running at 1500kbps bitrates, but also I have run 1000kbps too. I've been running 2hr movie encodes with both RDO B-frames and BiME enabled and doing 5+ fps on the second-pass with a 3Ghz P4.

That option will slow you down significantly, however, it may not be helping you out. Try this.

Fourth Test:
800kbps
Multi Hex
No Fast Pskip: unchecked
RDO Bframes: enable
Bi ME: enable
5 Mixed Ref
Soul V2 and Flat 16

[Caroliano]

I'm seeing how far I can stretch the HQ-SLOW profileWhy you is doing it? Why not jump straight to HQ-Slower? Or it is too long jump, because it is much more slower than you want?

[foxyshadis]

The difference between slow, slower, and slowest by default are only a few settings (well, and I think 3-pass starts on slower or slowest). By turning on some of these options you're just turning slow into slower anyway, the profile's name isn't going to make it any faster.

[JarrettH]

I guess the profile is irrelevant, it's just what I started on...only difference between this and slower is slower uses 10 reference frames and No Fast Pskip is disabled

I'll try that for a fourth test thanks :)

I saw SOME blocking, but then again I was looking at it on an LCD in the other room, not my CRT.

[Caroliano]

I know. But I think it is easier to him just jump from a profile to another, because they already have probably the best setings for that speed. And 3-pass is only in the Insane profile.

[JarrettH]

Responded at same time :cool:

I didn't want to use slower because anything over 5 ref is excessive from what I read here and googled, plus I don't want to bog down the decoding speed.

[rushin_911]

Responded at same time :cool:

I didn't want to use slower because anything over 5 ref is excessive from what I read here and googled, plus I don't want to bog down the decoding speed.

Actually I think I've read somewhere on the forum that using more than 5 refs is useful with the mixed-refs option...

[Caroliano]

Mixed references realy make more references useful. Especially for animation, where even 16 references still improve the compression sometimes. And you can use the slower minus the number of references that you want. Also an option.

[JarrettH]

Right about that. The only threads I could find suggested the same. So I took off mixed and left the rest checked.

I ran Multi twice using SoulV2 and Flat16 (default) and Hex twice using SoulV2 and Flat16.

- Not that I need to confirm this; Multi-hex is definitely only beneficial for those fast motion scenes, I had trouble spotting the differences between identical frames. I don't think there were any differences using Multi-hex even in fast motion scenes with this movie
- Multi-hex added 1hr to encoding time (that's it?!)
- Basically 10hr vs 11hr
- Flat16 does produce a brighter picture (is this more correct though?)
- SoulV2 is slightly more detailed and less gradient looking in certain areas (especially skin)

[JarrettH]

More update:

For fast motion and if the movie is around the same length (100min or so) I'd use:

800kbps
Multi Hex
No Fast Pskip: checked
RDO Bframes: enable
Bi ME: enable
5 Ref
Soul V2

For slow motion

800kbps
Hex
No Fast Pskip: checked
RDO Bframes: enable
Bi ME: enable
5 Ref
Soul V2

I kept the AC3 (2ch) file and transcoded it to AAC using transcode quality + pregain with BeLight which produced a 93mb 2ch file. I'm not one to butcher the original audio, but you COULD use HC-AAC profile and get away with 840kbps in the video data.:scared:
If I were doing a 2hr+ movie I'd skip right to 2cds whatever bitrate it works out to be plus the same settings above. About 10hr encoding time on a P4 3.0GHz for Hex, 11hr for Multi-hex. Perhaps uncheck no fast pskip since high bitrate.

And thank you guys SOOOO much throughout the weeks. I've learned so much, now I can use the encoder as if it were XviD (used for a long time previously :)