Scene Detection: Turn it on?

[TomBrooklyn]

Turn it on or leave it off - what say you?

What does it do anyway? (in non-technical terms, please)

[jdobbs]

It's generally better to have it on. Suppose the encoder is chugging along creating Groups of Pictures (GOPs) that are 12 long... the GOPs include an I frame followed by eleven P & B frames. Because of the way P & B frames work, normally when you have a dramatic change in the source -- like a scene change -- it is better to create a new I frame and start a new GOP. Scene change detection does that for you.

[TomBrooklyn]

Wilco. Thanks jd.

[manolito]

Quite a while ago I had a discussion about scene change detection with Nic (author of QuEnc). The QuEnc tool tips recommend setting scene change to OFF and closed GOPs to ON. Nic said that while enabling scene change detection can (slightly) enhance quality, QuEnc might create some very short GOPs that standalone players might not like. And for QuEnc Nic is right! Just the other day I did an encode with QuEnc 0.61 with a very high average bitrate (around 7.500). Using 1pass VBR with scene change on I got some stutter on my cheapo Cyberhome standalone (which is very forgiving, it swallows about everything you feed it). Turning scene change off and closed GOPs on took care of the stutter, and I could not detect any difference in quality.

Cheers
manolito

[TomBrooklyn]

The QuEnc tool tips recommend setting scene change to OFF and closed GOPs to ON. Nic said that while enabling scene change detection can (slightly) enhance quality, QuEnc might create some very short GOPs that standalone players might not like.
Hi manolito,
Could you share a link to those tool tips? I'd like to read them.

It sounds like I might be wise to burn to an RW and see if Scene Detection runs OK on my player which is a Panasonic S35 before I make a final copy.

For any future players that come on the market, would they be more or less likely to not accept Scene Dectection well or is it impossible to say? I would assume the newer the player, the more it would tend to be able to handle.

[jdobbs]

@TomBrooklyn

Well, if Nic says to turn it off for QuEnc, I'd do it... but for HC and CCE I'd leave it on.

[manolito]

@TomBrooklyn
Just start QuEnc and click on "Advanced Settings". Move your mouse over the area where you toggle SceneChange and ClosedGOPs, and voilá, ToolTips!

And I agree with jdobbs that for CCE and HC the story is different. Out of curiosity I redid the encode which caused stutter with both CCE and HC (with SceneChange ON and ClosedGOPs OFF). CCE behaved normally, while HC detected (and corrected) a lot of buffer underruns (over 400). HC was very slow because of the underruns, but the result was flawless.

Cheers
manolito

[TomBrooklyn]

@jd: OK, I'll just leave it off. I won't mess with it unless I have some compelling reason to think it's OK in the future. :thanks:

@manolito: I never opened QuEnc before. I asked about Scene Deletion because it was an available option in Rebuilder. Anyway, I found and opened QuEnc. I have version 0.61. I clicked on "Advanced Options" (I assume that's what you meant. There is no 'Advanced Settings'.)

But anyway, holding my mouse of the GOP/Scene Deletion area didn't open anything up. I tried right and also left clicking in this area to no avail also. :confused:

[Jeffster]

I've never used QuEnc and it may indeed be different to CCE in this regard, so this may not be helpful to you... but in CCE, auto scene change detection is the default setting and close all GOP's is off by default. The CCE manual recommends not to change these settings unless you have a compelling reason to do so (e.g. multiangle video).

BTW. I also have a Panasonic S35 and never had a stutter problem with any of my CCE encodes, ever. :)

[manolito]

@TomBrooklyn
You have to move your mouse right over the scene detection or closedGOP checkbox, no need to click any button.

@Jeffster
You might want to check out this thread:
http://forum.doom9.org/showthread.php?p=658817#post658817

Cheers
manolito

[Jeffster]

Thanks manolito, that's an interesting read :)

[laserfan]

...Out of curiosity I redid the encode which caused stutter with both CCE and HC (with SceneChange ON and ClosedGOPs OFF). CCE behaved normally, while HC detected (and corrected) a lot of buffer underruns (over 400)...Sorry but I don't understand--there is no "SceneChange" option with the HC encoder! Or is there???

[Carpo]

@TomBrooklyn

Well, if Nic says to turn it off for QuEnc, I'd do it... but for HC and CCE I'd leave it on.

where are these options - or are they hidden ini file settings ?

[jdobbs]

The setting for QuEnc is in the Options menu. I'd forgotten, until you mentioned it, that I didn't have it as a switch for the other two. It's in the created ECL file and HC.INI file...

[dialysis1]

Can any one tell me what would be a good HC.ini file? The only thing in mine is *bias 20.
Should there be more lines?

[jdobbs]

If you're using DVD-RB it really doesn't matter whats in it. In the Pro Version an HC.INI file is generated on the fly with the proper settings for each encode. In the freeware version parameters are passed on the command line (QuEnc style).

[Carpo]

where is the ecl file would the setting in question be ? - im not the best in the world when it comes to backing up stuff or decrypting all the settings in the ecl ;D

[jdobbs]

I wouldn't recommend changing it (except for ILVU, and DVD-RB does that automatically).

It's controlled by the line:

fix_gop_length=0

[dragongodz]

just a small comment. with QuEnc ,infact any of the encoders, closed gop is not needed unless you are doing a multiangle film. then it is required by all. DVD-RB should automatically set that so you shouldnt have to worry about it.

i dont know why Nic made the tooltips suggest closed gop on.