HMC-150 Exported Footage to m2v "twitches" (Clip Included)

T

The Irish TRex

Well-known member
Hello Helpful People!

For some reason, when I export this Wedding I shot (720p) from FCP 7 to Compressor to make a DVD it twitches for about a minute at 2 or 3 different times in the video. I have exported several 720p and 1080p weddings prior to this with no issue. The twitch is NOT present in the source video and never comes up when I export it to QT or to mp4 via Compressor, etc. Below you'll see the link to a section of the clip (on VIMEO) to see what I'm talking about when I say "twitch".

One interesting thing about this is that I tried exporting the whole video to m2v at several different settings and there was no rhyme or reason why this is happening (see the exports below). Fortunately a couple of the exports of this Wedding didn't have the "twitch" issue so I was able to burn the DVD and move on but this makes me nervous going forward.

ALSO! I tried exporting ONLY the portions that twitched by cutting and pasting them to a new sequence and exported them at the settings below and it did NOT twitch at all. Only when the full video was exported at the settings below did the video have the twitch issue...strange.

The twitch happened in the same areas on all the videos (except the couple that didn't have it at all) and it always lasted for about a minute or so then went away only to come back later.

Again, I have done several weddings before at these settings with no issue.

Exports to DVD 2-pass directly from FCP to Compressor:

6.8mbps 8mbps max: Twitches EVERYTIME I export it at this setting (but not on other weddings)
6.6mbps 7.8mbps max: Twitches in the same few places
6.7mbps 8mbps max: NO Twitch on this export for some reason (strange)
6.4mbps 7.7mbps max: NO twitch
6.9mbps 8.1max: Twitches in the same few places



Any ideas on what is causing this for this video?

Here is the link to a portion of the clip that has the "twitch":


http://www.vimeo.com/16037547



Thank you all for your help!
 
It seems to me that the twitching is a lot of macroblocking, like compression artifacts, right? And they happen consistently about every second, right? (Just making sure we're referring to the same thing)

In that case, I'd point the culprit toward the keyframes that are inserted into any long-GOP compression format like H.264 - by default, once per second. Maybe they are, for whatever reason, being inserted a half-frame early or something screwy like that.

That might explain why the footage only does this in the context of the long timeline - it may take that long for the error to catch up to you, and take a minute or so to dissapate again.

Why you're the only person to encounter this is beyond me. You could try trashing your FCP preferences if you're desperate. I'd be curious to see what happens if you change the keyframing setting to match your framerate, or set it to auto, etc?
 
Hi TigerFX,

Thanks for responding. Yes, the twitch as you can see on the video is every second or so. I guess I could trash my FCP preferences. Oddly, this never happened on any other video I've cut from my HMC150's and they are usually much longer than this video. At least I don't think it happened on those videos :/

As for keyframing setting, I don't see how to change that at all in Compressor given that I'm exporting it to mpg2 (m2v) for DVD and I don't see any place to adjust keyframe settings. This is all very strange.
 
Trashed preferences. Exported again. No luck.

The twitches are actually about 2 per second as you can see and again, occur in the same few places in the video. Strangely, I was able to export it without the issue as you can see in my original post but most of the time this twitch appears. Its only a 22 minute video. I've had much longer ones that didn't have this issue when converted to m2v files for DVD.

Any ideas? ...anyone.
 
Where are all the FCP guys?

If you don't get an answer soon, make a post bashing Apple & FCP... THAT will get attention around here!:shocked:
 
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