All clips where an identifiable human face is present require a model release. There are no exceptions. In some cases a release may be required even if the face is not identifiable. Please see the 'Contextual Model Releases' section of this article for a complete explanation.
If the clip is of a minor (a child under the age of 18), a model release must be signed by a parent or legal guardian.
If the clip is of the videographer, a model release is still required.
A model release should be uploaded with each file. If you're uploading successive clips of the same model, the model release should be uploaded with each clip.
A valid witness signature must appear on the model release. Generally, it should be someone other than the videographer.