Few I have considered:
1: Upload raw video to Amazon S3/GCS -> Zencoderencoder -> save back to S3/GCS-> Serve through CDN(upside:reliable), (downside:expensive and round-tripping extra bandwidth)
2: Upload Raw video to Vimeo PRO-> serve directly through Vimeo CDN(upside: No bandwidth limits) (Downside: Storage Limits)
3: Upload To Amazon S3 -> transcode with zencoder-> upload to vimeo(upside: raw video never stored on vimeo)
What are other startups using for their User uploaded Video files?