Premiere Pro attempts to play back any sequence in real time and at full frame rate. Premiere Pro usually achieves this for all sections that either need no rendering or for which Premiere Pro already has rendered preview files. However, real-time, full frame-rate playback is not always possible for complex sections without preview files: unrendered sections.
To play back complex sections in real time and at full frame rate, you may have to first render preview files for those sections. Premiere Pro marks unrendered sections of a sequence with colored render bars. A red render bar appearing in the time ruler of a sequence indicates an unrendered section that probably must be rendered in order to play back in real time and at full frame rate. A yellow render bar indicates an unrendered section that probably does not need to be rendered in order to play back in real time and at full frame rate. Regardless of their preview quality, sections under either red or yellow render bars should be rendered before you export them to tape. A green render bar indicates a section that already has rendered preview files associated with it.
Sequences refer to preview files in much the same way as source media. If you move or delete preview files in the Windows or Mac file browser rather than the Project panel, you’ll be prompted to find or skip the preview files the next time you open the project.