First, you didn't use version 10 to open a project you created in version 9, did you? We always recommend against opening an older version project with a newer version of the program. It almost always leads to problems.
Second, what model of camcorder is your video coming from and what format and resolution is it?
And, when you started your Premiere Elements project, which project settings did you select? If you selected the right project settings for your video, you will NOT see red lines above your clips when you first add them to your timeline. Is that the case in your project?
Finally, have you ensured that all of your photos are sized to no larger than 1000x750 pixels?
Steve, thanks for your response. I created this new in version 10. The video and stills are from a Canon 5D Mark II, the video at 1080/30 (I selected the 29. whatever, the actual frame rate), H.264, and the stills were resized (perhaps this is the issue) to 1920 pixels max size, as I knew I needed to reduce them and thought that matching the video size would be maximizing the resolution possible. I see you are saying 1000x750. Is that really the max size allowed? I never saw a max size anywhere when I looked at the time. The project settings were "DSLR-1080p-DSLR 1080p30 @ 29.97." My Timeline has an almost continuous red line above it now, though it didn't at first. The first couple of minutes will play in preview, then the preview freezes while the timeline thing right under the preview, and/or the Timeline, it that is showing, continue. If in Sceneline, that stops too. Thanks so much for your help with this.
Remember to render your timeline (press Enter) whenever you see red lines above your timeline.
When those lines turn green, your timeline should play much more smoothly.
Also, you will want to Scale the Still Images from the Canon to match your Video's Frame Size, say 1920 x 1080, in Photoshop, or Photoshop Elements, prior to Importing them into PrE.
I see you are saying 1000x750. Is that really the max size allowed? I never saw a max size anywhere when I looked at the time. The project settings were "DSLR-1080p-DSLR 1080p30 @ 29.97."
The max size suggestions are that - suggestions. I think the PRE specifications say much higher. The difficulty is that PRE does not perform well on downsizing large still images and typically crawls along or crashes. Steves recommendations are based on long experience so try them out. Note though that the 1000x750 is a suggested maximum is for an SD project. That you are doing an HD project you can double those to 2000x1500. The size gives you some latitude for pan and zoom but if don't plan on doing any pan & zoom go with Bills suggestion to resize them to exactly your intended output dimensions.
My Timeline has an almost continuous red line above it now, though it didn't at first.
That is an excellent result. The lack of an initial red or green line means that your preset exactly matches your clips. This will give you the best editing experience.
The red lines appear as and when you add titles, effects, transitions, or overlay one track or still over another .... i.e. the red line means you made changes and your edits can be rendered for best preview.
If, when previewing, the clip runs jerkily set the WorkAreaBar to cover the jerky part and press [ENTER]. PRE will render that segment for a better preview. You do NOT have to do this though if previews are smooth enough - PRE will always render the entire timeline during the Share process.
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As Neale points out, the "recommended sizes" are just that, "recommended." Also, the 1000 x 750 rec. comes from when most Projects were SD (Standard Definition) for either NTSC, or PAL DV, with Frame Sizes of 720 x 480, or 720 x 586. That recommended size allowe one some wiggle-room, and some limited Panning, on a zoomed-out Image.
With full-HD, the recommend size is 2000 x 1500, but I Scale those Images to exactly the Frame Size of the Project, say 1920 x 1080, unless I need to do a Pan on a zoomed-out Image, and then I calculate the extra pixels, that I need for my animation, and will even Crop the height, if the Pan is horizontal ONLY, to eliminate unused pixels.
Unless it has changed lately, the MAX Size is 4096 x 4096, but ONLY 1920 x 1080 can ever be seen at one time. If one is not doing heavy Panning, then there are unused pixels, and it does not take many 4096 x 4096 Images, before the computer will choke, due to the necessary processing of those unused pixels.
Also, PrE, though it can Scale Still Images, does not do nearly so good a job, as Photoshop, or Photoshop Elements. This ARTICLE goes into more detail, and will show how to Automate>Batch Scale entire folders.