Dealing with long GOPS (40+ frames)

[Shannock9]

(If this is in the wrong section please move it.)

UK DVB-T material seems to have longer and longer GOPS. 40+ is normal on some channels now. This leads to (at least) two problems when trying to set chapter marks.

1. The jump to next/previous I-frame routinely fails for longer GOPS. So I have to look for the I-frames by stepping frame by frame.

2. Every two seconds does not give sufficient granularity when setting chapters. Often I have to cut out a single frame in order to force VRD to re-encode so I can have a DVD chapter point where I want it - and success depends on the audio also. It would be nice if VRD would honour the chapter marks I set by re-encoding a little bit to make them valid I-frames.

Duncan

[phd]

You can set the maximum GOP length by clicking the Options button in the file save dialog box.

[halsboss]

I think you can do it with QuickStreamFix too (an option there, so it fixes the lot) ?

Hmm, what does that result in ... does it re-code or just cut out frames, I wonder ?

[phd]

It will recode just the necessary frames to create new I-frames

[Shannock9]

Thanks for the responses....but I don't want to reduce the GOP length throughout the file - it plays very well as it is and reducing it would make the file significantly larger. What I'm asking for is quite different:-

1. Please make the jumps to next/previous GOP work for larger GOPS.

2. Please recode around every scene marker so each marker becomes an I-frame if it wasn't already (perhaps as an option, though I can't see how anyone wouldn't want this).

[DanR]

This has been on the the low priority list for a while. I'll see if we can escalate it.

[Shannock9]

That would be appreciated. Though not to detract from work on the subtitles .

[Anole]

I don't want to reduce the GOP length throughout the file - it plays very well as it is and reducing it would make the file significantly larger.

Try it, you'll be surprised.
As long as you don't go crazy, it's not that much of a file size impact.
Maybe try 36, 24, and if you are really avid, 18.

As for myself, I set chapters at actual cut points where VRD re-encodes the cut anyway.
So I don't really need the fancy feature proposed.

[Shannock9]

Anole, thank you for the advice. I usually want the chapter mark on a scene change, which are not usually exactly on I-frames. So to force VRD to reencode I was deleting one frame from the cutaway which did not show.

However this techique can lose a subtitle if its PTS is near the deleted frame, so I thought why not ask for what I actually needed.

Dan, expanding on the "delete one frame", one way to architect this feature simply would be to treat chapter marks as requests to make a cut of zero frames at that point. Sounds weird I know, but try it on the developers and see what happens

Cheers, Duncan (Shannock9)

[Anole]

I understand your goal, and appreciate the idea.
Certainly wasn't dismissing the need to set chapters on specific frames (and have them work).
In fact, I think commercial editors used to master movies to DVDs do exactly what you suggested.

Was only saying that making shorter GOPs didn't increase file size all that much.
And, if as a temporary work around, it would help, then the short GOPs might be an option.
Obviously it'd help, but still be only to the nearest half-second.

I use chapters as a quick way to get somewhere in a two hour video.
So, precise navigation isn't my goal.
Jumping to the nearest (missing) commercial in a Formula One race is good enough.

Will be curious to see if the developers have given the idea any more thought . . .