Observation About Slo-Mo Quality

[Black Lab]

I should preface this by saying I am working with DV-AVI files and converting them to MPEG-2 to be burned to DVD. I don't know if these findings will hold true for other formats.

I just finished my first extensive project using X4. I was making a highlight video for my son's baseball team and I used some slow motion (in varying degrees) on a few clips. As is the case for many of the veterans on this board I still use the old "recommended workflow" of first producing a DVD-compliant MPEG-2 file and then inserting that into the burn module.

Upon completion of the rendered MPEG-2 file I noticed that the slow motion clips did not play back smoothly. Choppy does not accurately describe it, but it wasn't smooth either.

I then took the slo-mo clips and rendered each of them to a new DV-AVI file. I put these clips back into my project, in place of the original slo-mo clips. So, in essence, I was pre-rendering these clips so they wouldn't also have to be "slowed down" while they were being converted to MPEG-2. I again rendered the project to MPEG-2 and the slo-mo clips turned out smooth as silk.

Not sure if this is an anomaly of X4, as I haven't had a chance to try this workflow on previous versions. But if you are not happy with your slo-mo quality you might want to try this workflow.

[skier-hughes]

This is due to the way mpeg files are made.
dv.avi is made up of 1 real frame per frame
Mpeg2 is made up of 1 real frame about every 16 frames. (It does depend on the settings) In essence the frames between these real frames are "made up" or extrapolated. This is what gives mpeg the lower file size.

By saving your slow mo to dv.avi you make each of your slow frames a real slow frame immediately, whereas the mpeg compression is guessing at what is happening at the same time as slowing it down.

There, clear as mud

[Black Lab]

Hmm. I don't recall having issues before (with previous versions), but due to your explanation I think I'll keep with my workflow so as to produce the smoothest slo-mo.

Thanks.

[DVDDoug]

Mpeg2 is made up of 1 real frame about every 16 frames. (It does depend on the settings) In essence the frames between these real frames are "made up" or extrapolated. This is what gives mpeg the lower file size.

By saving your slow mo to dv.avi you make each of your slow frames a real slow frame immediately, whereas the mpeg compression is guessing at what is happening at the same time as slowing it down.

There, clear as mud

Makes sense... 'Till I think about it. Even when you are rendering to MPEG, It seems like the edits/effects should be fully-rendered before compression. I would have expected that identical full-frames would be feed into the MPEG encoder in either case.

But, I try not to think too much about what it should be doing, or what I wish it would do. I just try want to get the best out of it, or find an aternative or work-around when necessary.

[alanball]

Jeff,

are you saying that you rendered the mpeg slow motion files to avi and then put those back into you your project and re-renderd back to mpeg? Was there a loss of quialty?

[Black Lab]

No. I rendered the original DV-AVI clips with the slo-mo effect to another DV-AVI that I inserted in place of the original.

In other words, I took a 5 second clip and adjusted the speed to 50%, making it a 7.5 second clip. I then rendered it to another DV-AVI. The resulting 7.5 second clip plays at 100% speed.

[alanball]

Thanks Jeff,

interesting

[Kingston]

Jeff,

Initially when you shared to MPEG-2, without that DV-AVI to DV-AVI intermediate step, did you use custom settings and change the field order to Lower Field First to match the DV-AVI field order?

I bring this up because that workflow produces an MPEG-2 where the 50% slow motion makes me sick. When I shared to an MPEG-2 with field order set to Upper Field First, the slow motion was smoother and didn't make me sick.

It's not suppose to be that way.

[Black Lab]

Yes, I of course matched the field order.