How to make joint between cells seamless?

[Denis Fomin]

Hi.
I have the following matter I would like to ask your help with :)
Sometimes I cut out final credits, DVD Shrink them to "Still Pictures" to reduce size and add them back by using DvdRemake's "Replace block" function. DvdRemake somehow knows that replaced cell can continue last VID and doesn't allocate new VID. On the other hand sometimes I want to cut out some scene in the middle of a cell. For instance cut out credits song in the Friends series DVD. I split the cell containning credits and then cut the beginning of the second cell, but in this case DvdRemake decides that the second cell with the cut out beginning cannot be in the same VID and puts it in a new VID thus makes joint NON-seamless. In turn NON-seamless joint results in layer-break like pause on my standalone. Sorry for all that long preliminary story, my question is: how to make joint seamless and avoid this layer-break like pause? What is the reason new VID is needed and how DvdRemake decides it? Based on what?
Thanks in advance.

[Video Dude]

You can use PGCEdit to change the cell flags.

[mpucoder]

I don't know why DVDRemake is making a new VobID, but once that is done it is not possible to make the joint seamless by just changing flags.
It is not possible for a seamless joint between vobs to follow a still. But within a vob, stills can be followed by motion video seamlessly and new cells can start at the joint.

[Denis Fomin]

mpucoder
I'm sorry if my question was somewhat misleading, the main point is not so much stills as joint between any two cell. How can determine if a joint is seamless (and thus the flag in IFO is correct) or isn't seamless (and flag in IFO should reflect that), and if the second is the case what can I do to make it seamless? Maybe some remuxing will help?

[mpucoder]

One big indicator is the audio pts, if the first audio pts is less than the vobu_s_ptm it probably can be joined seamlessly to the previous vob. If the audio starts at the same time or later than vobu_s_ptm it is definitely not seamless.
Do the vobs created by DVD Remake start with SCR of zero? If they do not then they are not spec, but could probably be changed back to the old vobid.

[jsoto]

Cutting with DVD Remake (quoting Dimad) are not clean cuts.
To make (again) a seamless joint, means you have to cut exactly the same length in video and audio. Becasue the cuts are done w/o recoding neither video nor audio it is not possible to do a seamless joint.
I'm not sure, but probably DVD Remake cuts the VOBs in a GOP basis and the audio just in the packs muxed in the GOPs to be cut. This is how VobBlanker works, and it also makes a non-seamless joint, to avoid a/v synch problems after the cut.
jsoto

[Dimad]

DRM cuts are also on GOP boundaries.

[jeanl]

Cutting with DVD Remake (quoting Dimad) are not clean cuts.
To make (again) a seamless joint, means you have to cut exactly the same length in video and audio. Becasue the cuts are done w/o recoding neither video nor audio it is not possible to do a seamless joint.
I'm not sure, but probably DVD Remake cuts the VOBs in a GOP basis and the audio just in the packs muxed in the GOPs to be cut. This is how VobBlanker works, and it also makes a non-seamless joint, to avoid a/v synch problems after the cut.
jsoto
jsoto, technically, it might be possible to do a seamless joint, by replacing a few of the last audio packs right before the cut with audio packs taken from the end of the zone you're cutting. I'm not saying that would be easy, but my guess is that you could achieve seamless playback without having to re-encode.
I really don't think that's worth the trouble though...
jeanl

[jsoto]

jsoto, technically, it might be possible to do a seamless joint, by replacing a few of the last audio packs right before the cut with audio packs taken from the end of the zone you're cutting. I'm not saying that would be easy, but my guess is that you could achieve seamless playback without having to re-encode.
I really don't think that's worth the trouble though...
jeanl I know what are you saying, but in any case the length of a VOBU is in video frames (40 msec in PAL) and the frames of the audio can be DD (32 msec) mpeg (24 msec) DTS (10,66 msec) or LPCM (don't remember now the number..)
You can try to do a seamless join (with a lot of work), but that means the audio will be played w/o any interruption, so a minimum a/v synch difference will appear. And, as a side effect, the audio PTSs will not be OK, you'll need to change them, and as consecuence, you have to change SCRs and also move the following audio packs inside the VOB, just like you're muxing again..... Really, really difficult.

jsoto

[jeanl]

You're right, I didn't realize that audio frames sizes didn't match video frame sizes (at least they're not simply related). This pose a pretty serious problem!
Jean

[Denis Fomin]

How about remuxing the streams? Will that work? Maybe it's the easiest solution?

[jsoto]

When you demux a non-clean cut, uncomplete audio frames could appear just in the cut. You have to clean the audio, (run ac3fix or delaycut) and you'll have the audio w/o errors.

But the audio will not be exactly in synch with the video, due the differences in the frame length of audio/video. (May be you cannot notice it, in only one cut, but the error could be accumulated along several cuts)

So the current way to do the joint, a non-seamless one, is, IMHO, the only way to guarantee a perfect audio/video synch after the cut.

jsoto

[Denis Fomin]

I was afraid of that :( Well I'll wait. Maybe some solution will appear :)
Anyhow thanks you guys for all the replies.

[blutach]

This is actually related to an issue with VobBlanker (http://jsoto.posunplugged.com/vobblanker.htm). For example, say I cut the credits (which are in the final cell) in "keep movie" mode - say halfway through the credits.

VobBlanker (http://jsoto.posunplugged.com/vobblanker.htm) makes the final cell non-seamless, even though its entry point is (I assume) muxed correctly as a seamless joint.

Is is safe to change it back to seamless in this situation? Just apply mpucoder's rules?

EDIT: The 1st audio pack's PTS is 1 less than the VOBU_S_PTM in the nav pack, so I guess I am OK. So maybe this is something for VobBlanker (http://jsoto.posunplugged.com/vobblanker.htm) to check before it makes the cell non-seamless?

Regards

[jsoto]

For example, say I cut the credits (which are in the final cell) in "keep movie" mode - say halfway through the credits.
VobBlanker (http://jsoto.posunplugged.com/vobblanker.htm) makes the final cell non-seamless, even though its entry point is (I assume) muxed correctly as a seamless joint.
Uuh. Sure?

This is what VB should be doing. Note you are talking about CUT2 mode

if (iCutMode==CUT1 || iCutMode==CUT3)
{
// Mark this cell as non-seamless
}
if (CutMode==CUT2 || CutMode==CUT3 || CutMode==CUT4 )
{
// Mark next cell as non-seamless
}


Cutmode=CUT1 means
"Keep from here"
So this cell is marked as non-seamless and next cell is untouched

Cutmode=CUT2 means
"Cut from here"
So this cell is untouched and next cell is marked as non-seamless

Cutmode=CUT3 means
"Keep inside"
This and next cells are marked as non-seamless

Cutmode=CUT4 means
"Cut inside"
This is a little tricky..., next cell is marked as non-seamless. This is not really true, but the cut inside is not clean so a minimum a/v synch prob can be there...

jsoto

[blutach]

@jsoto

Mark 1 was from the start of the movie (cell 1 start)
Mark 2 was halfway through the last cell

The last cell was marked as non-seamless :(

Regards

[jsoto]

@blutach
I did some test and I was unable to reproduce...It works for me as I'm expecting...

Could you send me your IFOs before/after and VBlanker's project file?

jsoto

[blutach]

That may be difficult as the project is now off my system (can't remember which DVD it was actually).

Next time it happens, I'll email you. :)

Regards