Rendering to MOV, new scenes all start blurry

fherr wrote on 10/3/2006, 5:57 AM

Just returning to video, glad to see this forum is still as great as I remember it - can someone please point me to solutions for this:

I'm rendering to QuickTime format for the web, trying to get the file size down, but in the resulting MOV, every new scene starts really blurry, and then comes into focus only after a second or two. What parameter in the rendering settings controls this? I've been experimenting without success so far.

Here's what I used last:
Frame size: 320x240
Frame rate: 15
Field order: none
Pixel aspect ratio: 1.000
Video Format: Sorenson 3
Quality: 100%
Data Rate: basic
Target rate: 56
Keyframe every: 15

Any tips would be appreciated. Is there a good web site that gives rendering tips like this? Having trouble finding that too ...

Thanks a lot,
- Frank

Comments

fherr wrote on 10/4/2006, 9:44 AM

I'm guessing my question wasn't clear, so I'll try rewording:

What are the best render settings, for making quicktime (MOV) files for the web, that keep the file size down but the video images sharp?

Whenever I use settings that achieve any kind of significant reduction in file size, the resulting video is blurry at the start of every new scene. Has anyone else experienced this? How did you fix it?

Thanks in advance,
- Frank

Chienworks wrote on 10/4/2006, 5:20 PM

56 is very very low. I'm surprised you get a usable image at all. Probably most folks would consider 256kbps to be the minimum acceptable rate for 320x240 15fps. If you want to keep the rate that low then you'll have to use a smaller frame size and a slower frame rate. Try 160x120 at 10fps and see if that helps.

The problem you are seeing is that at lower bitrates each frame depends very heavily on reusing information from previous frames. This works ok when the scene is more or less constant. However, when a scene changes or there is lots of fast motion the next frame is completely different from the previous frame. At 56kbps there isn't enough data available to draw a whole new frame all at once. The first frame will be a very poor approximation of the original image and it will take a few moments for enough data to be accumulated to recreate a credible image again.

fldave wrote on 10/4/2006, 7:54 PM

Sounds like maybe an overlap/transition between the scenes. Or it may be just a difference between source footage (29.97fps) and target rate (15).

To the extreme, I captured 1(one) fps software training demo and encoded at 15fps. The result was a "blending" transition where Vegas had to create the interim frames between the two. Smooth, mostly, but a few times it seemed "wrong".

If your scenes start with static images/frames, then that may be what's happening.

fherr wrote on 10/5/2006, 7:42 AM

Thanks very much Chienworks, that really helps me understand what's going on. My video does indeed have many scene changes. I'll try re-rending today at some higher rates.

fherr wrote on 10/5/2006, 7:44 AM

Yep, lots of my scenes also start with static images. Thanks for the tips, fldave.