Media presentation playback annotation

Annotations can be automatically added to a media presentation during playback of the presentation without a user having to manually interact with the playback device. The playback device determines whether an annotation is to be added to the media presentation based on characteristics of voice input received at the device, such as voice input signal strength or variances in the voice input signal strength. Characteristics of video input received at the device can be used to determine whether a user is speaking to the computing device as well. The device can handle a new annotation overlapping an existing annotation by either removing the existing annotation or by shifting the existing annotation until there is no more overlap. A media presentation can comprise multiple annotation tracks.