gio
2004-11-04 08:30:57 ( ID:h.0/kudvuvo )
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Hallo
I want to know if is possible to change the Iframe GOP (every 15frames default)
The reason is because I cannot make frame accurate chapter in authoring DVD.
I work in PAL (25fr/sec) and it should be better (and logical) if the Iframe would be every 5 frames.
Thank for your answer.
Giò
B_Racer
2004-11-04 09:17:58 ( ID:0jd4rmr3tyn )
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Sure you can change this. No problem so far. But on shorter GOPs, you need more Bitrate to get high quality.
You can also force TMPGEnc to set frames you want as I-Frames. That's done by using force picture type setting.
And on some Authoring tools like DVDLab, you are able to use Frame-indexed Chappter settings.
ashy
2004-11-04 19:04:56 ( ID:jitozw1gquh )
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What you intend to do will seriously increase the size of the output if you use a VBR method and will also need a higher bitrate if you use a CBR method. Surely a chapter every 15 frames is enough, that's almost one every half a second.
If you need the odd specific chapter then use the 'force picture type setting' as suggested.
gio
2004-11-09 12:06:19 ( ID:h.0/kudvuvo )
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Hello, Ashy, how are you?
I hope fine.
Thank for your answer.
15frsec is a 30frsec (NTSC) splitting second.
PAL is 25frsec. GOP every 10fr or 5fr will be better for PAL videos.
What, exactly, is affected from this change? Quality? Jittering? Blocking?
Pixelation?
Thanks
Giò
ashy
2004-11-09 17:28:47 ( ID:jitozw1gquh )
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>GOP every 10fr or 5fr will be better for PAL videos.
No not really. I don't know why you think this.
In fact it can have a detrimental effect on the quality.
Also the frame rate doesn't really matter to the GOP length. A GOP is created per the set GOP length or at a scene change.
DVD's are limited by the bitrate they can handle.
Use too many I-frames in a GOP and the bitrate runs short causing blocks and pixelation effects.
Most commercial DVD's use a length of 12-15 frames in a GOP.
I would prefer 15 myself because of the better compression and higher bitrates that can be used when using 4.7GB disks.
ashy
2004-11-09 17:36:11 ( ID:jitozw1gquh )
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>Use too many I-frames in a GOP and the bitrate runs short causing blocks and pixelation effects.
Sorry that may not make sense to you. I know what I was driving at in my head, but explained it wrong.
What I mean is that each GOP has an 'I' frame, the shorter the GOP the more 'I' frames are created. The more 'I' frames the higher the bitrate needs to be and thus larger file size and/or pixelation.
gio
2004-11-10 08:00:11 ( ID:h.0/kudvuvo )
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Thank you, Ashy.
The reason of my question is to have more chances to choose the right I-frame (for chapter) without take the beginning or the final of a cross dissolve or a video effect.
Probably, at every 12fr/sec, could be the right way for PAL_video. What is your opinion?
Giò
ashy
2004-11-10 21:01:32 ( ID:jitozw1gquh )
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Well I suppose you could get away with it as long as the movie isn't too long. However as has already been mentioned you can force an 'I' frame wherever you want, so if you where to say add 20 chapters to the movie, you could decide where those chapters would be without sacrificing compression efficiency.
The only way would be to just try it and see how things turns out.
Gio
2004-11-12 10:33:49 ( ID:h.0/kudvuvo )
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OK!
I'll make a try and then I'll notice to you the results.
However the movie is 32min long and, for the "Murphy's Law", some chapters go in the middle of 10fr cross dissolve....
Thank you and Ciao.
Giò
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