Like all files in CONTENTdm, access on the website can be impacted by relative network speeds and file size. If video files take a long time to buffer, try accessing the collections on a different network first. If the network is not the issue, investigate the original file that was uploaded.
Try uploading a smaller test file to see if it suffers from the same issues. Reducing the quality and file size of the hosted video file will greatly impact accessibility. If this doesn't work, contact OCLC Support with the name of the collection and the link to the impacted item for additional assistance.
Please see CONTENTdm Video Best Practices.