edX recently commissioned a study of nearly 1,000 videos, segmenting them out by by video type and production style, and discovered this among their other findings:
- Shorter videos are more engaging. Engagement drops after 6 minutes.
- Videos with a more personal feeling are more effective than high-fidelity studio recordings.
- Videos in which the instructor speaks quickly and with high enthusiasm are more engaging.
- Khan-style tablet drawings are more engaging than power point slides.