Jerky movement when playback speed set slower for a clip

[jparnold]

To Gorf and others,

I recently posted a topic asking why a reversed clip plays back in a jerky motion.

I have solved my problem but I'm not sure how.

What I did was to reverse a length of video which contains a few clips (instead of just the clip I wanted reversed) and saved as an AVI file (lower field first). I also did the same saving as an AVI file (upper field first) just for a test.

I then dragged each of the two reversed clips into another project and 'cut' (mark in and mark out ) the clips I wanted from each of the two 'test' files. I added the original forward motion clip onto the same timeline. I then rendered and created a DVD and played it on my DVD player and TV. NO PROBLEMS with either of the reversed clips (lower field first or upper field first). ALL clips played smoothly.

I then wondered if it has anything to do with cutting the scene from a longer reversed clip rather than just inserting the full reversed clip.
BUT I also noticed that my original reversed clip was LONGER than the original forward motion clip which made me wonder if somehow the SPEED of the clip was somehow set to a LOWER speed than original when I applied reverse. I certainly did NOT knowingly change the spped before I saved the clip.

Anyway the problem sems to have been solved but it is still quite strange to me.

Cheers
John

[Maukka]

I am having exactly the same problem... with MSP 7.3. (Before reading your post I just had the time to post a question about this).

I have a complex 40 minute timeline which I have rendered about 50 times without problems. I always used 2 pass encoding.

Now I did some edits to two clips within this timeline. One I reversed and the other I slowed down. I also changed the length of both clips. And they turned out jerky. But the really weird thing is that the jerkyness continued even when I turned the speed back to 100 per cent.

I then replaced the slowed down clip with another which I copied from an older project file, to make sure I got rid of any edits I had done to it. So now it was sure to have the original speed and other settings (and it had rendered ok before). --And it still turned out jerky!

After testing I discovered that if I now render using one pass encoding (CBR) with bite rate 8000, the two clips in question turn out smooth. But if I use two pass encoding, they are jerky. So this is an encoding problem, for some rreason the Ulead codec cannot handle the clips. What remains a mystery is why the jerkiness was still there even after I had replaced the clips...

For my project two pass encoding is not necessarily needed, in terms of space on the DVD. But will I lose some quality if I use one pass encoding?

Thanks,
Maukka[/b]

[jparnold]

Maukka,
What are you using to render your movie? You say that you use two pass encoding.
I originally posted a problem with jerky playback of a clip I reversed (which was just one scene of a 45 minute movie) but that seems to have fixed itself (or did I do something different?). I noticed after I posted that the reversed clip appeared to be longer than the original (forward motion) clip which made me think that somehow the clip must have had it's playback speed slowed. I then 'cut' a longer clip than required (from the original captures video), applied reverse then saved the reversed clip as an AVI file. I then added this reversed clip to another priject and marked in and out a portion of that reversed clip to the lengthb I required and had no problems. Hope I explained that ok.
PLEASE NOTE that I use VideoStudio v8 to do my main editing as I find it easier to use than MSP. I only use MSP7 to reverse clips or create moving path to a clip which I then save as AVI files (to be later added to my project using VideoStudio).

[Maukka]

Hi,

I use MSP 7.3 for rendering, but unless I am mistaken Video Studio uses the very Ulead codec, which I think could somehow cause the video to become jerky when MPEG compression is done with two pass encoding. I render the speed reduction directly from the timeline, so I don't create a separate avi file first. But obviously, when yuo slow down the clip, it becomes longer... so I also did cut it.

I just now rendered my entire project using one pass encoding (constant bit rate 8000) and it turned out fine, including the clips which were jerky after two pass encoding. So I conclude that this is linked to two pass encoding.

Could it be that the Ulead codec's two pass encoding does not handle correctly slow motion created by changing clip speed in MSP? Then again, I have used the same "slowing down" method on another clip earlier, and it has always rendered fine. So it is not this simple...

So here's some further speculation: Another edit I did at the same time as this "slowing down" was to add some rather complex transitions relatively near to these problem clips in the timeline. Could it be that the two pass encoding wants to keep max data rate for the more demanding transitions and tries to get away with a much lower rate for what it considers more simple bits. And that it would somehow be tricked to using a too low data rate for the bits which have been slowed down in MSP....

Is what we perceive as jerky video actually just the clip being played first at normal speed and then all of a sudden in the slower speed (or the other way round)?

BTW, the jerkiness is NOT linked to any viewing device: it appears whether viewed on computer or on a set-top DVD player.

Debugging this problem could take days or weeks... And since everything looks good after one pass encoding, I really don't mind using that.

But I would like to hear from some authoritative source that in principle this (one pass CBR vs. two passes VBR) does not imply loss in image quality. My understanding is that two pass encoding is really interesting only when your project is long enough so that it becomes diffcult to fit it on a DVD. But when a project is only 41 minutes long this should not be an issue.
But I would like a confirmation to this... Anybody?

Thanks,

Maukka

[jparnold]

Have a look at (web site) http://www.videohelp.com/
You might get some help there.
I have in the past used TmpGenc to encode to both SVCD and DVD using various encoding methods (constant bitrate, variable bitrate, two pass VBR, constant quality, etc etc) without experiencing and real problems. I now just use the encoding 'engine' in Videostudio as most of my movies would not fit my hard disk in AVI format (I used to output from early versions of Videostudio to AVI and then render with TmpGenc).

[Devil]

Hi,

I use MSP 7.3 for rendering, but unless I am mistaken Video Studio uses the very Ulead codec, which I think could somehow cause the video to become jerky when MPEG compression is done with two pass encoding. I render the speed reduction directly from the timeline, so I don't create a separate avi file first. But obviously, when yuo slow down the clip, it becomes longer... so I also did cut it.

I just now rendered my entire project using one pass encoding (constant bit rate 8000) and it turned out fine, including the clips which were jerky after two pass encoding. So I conclude that this is linked to two pass encoding.

Could it be that the Ulead codec's two pass encoding does not handle correctly slow motion created by changing clip speed in MSP? Then again, I have used the same "slowing down" method on another clip earlier, and it has always rendered fine. So it is not this simple...

So here's some further speculation: Another edit I did at the same time as this "slowing down" was to add some rather complex transitions relatively near to these problem clips in the timeline. Could it be that the two pass encoding wants to keep max data rate for the more demanding transitions and tries to get away with a much lower rate for what it considers more simple bits. And that it would somehow be tricked to using a too low data rate for the bits which have been slowed down in MSP....

Is what we perceive as jerky video actually just the clip being played first at normal speed and then all of a sudden in the slower speed (or the other way round)?

BTW, the jerkiness is NOT linked to any viewing device: it appears whether viewed on computer or on a set-top DVD player.

Debugging this problem could take days or weeks... And since everything looks good after one pass encoding, I really don't mind using that.

But I would like to hear from some authoritative source that in principle this (one pass CBR vs. two passes VBR) does not imply loss in image quality. My understanding is that two pass encoding is really interesting only when your project is long enough so that it becomes diffcult to fit it on a DVD. But when a project is only 41 minutes long this should not be an issue.
But I would like a confirmation to this... Anybody?

Thanks,

Maukka

You should keep the subject to a single thread.

See my reposne in your other thread