Long compose timelines render to the end

Two limits inside the compose engine that only a long timeline reaches.

• A still can be held past 500 seconds. A clip showing one image for more than 15,000 frames, which is 500 seconds at 30 fps, went black at that point. When nothing else on the timeline ran that long, the video also ended early and the job failed with RENDER_INCOMPLETE. Stills and the timeline background now last as long as the clip asks.
• Slideshows with many transformed stills finish. A timeline of around 90 or more stills that each carried a transform could fail part way through at 720p and above, with RENDER_EFFECT_FAILED or RENDER_FAILED. The same stills in shorter timelines rendered fine, which made it look like a problem with one image. A 15-minute timeline of 113 stills with zooms and pans now renders in one job.
• Failure messages point the right way. RENDER_INCOMPLETE no longer suggests a retry, because the same timeline gives the same result. RENDER_FAILED no longer asks you to check your assets when nothing suggests they are at fault.

If you split a long slideshow into parts to get it to render, you can send it as one timeline again.

Timelines, clips and transforms are covered in the compose docs.