34. The system of claim 30 , wherein the rendering engine is operable to receive one or more user-specified categories for ones of the audio summaries while the audio summaries and the transition audio segments are being rendered.
30. An audio processing system, comprising a rendering engine operable to perform operations comprising: identifying audio summaries of respective audio pieces, wherein each of the audio pieces is associated with respective ones of audio summaries ranked into different levels of a respective audio summary hierarchy and in the identifying the rendering engine is operable to identify the respective levels into which the audio summaries are ranked; determining transition audio segments each comprising a form of audio content that is different from the audio summaries and distinguishes the transition audio segment from the audio summaries; concatenating the transition audio segments and ones of the audio summaries ranked at a selected level of the audio summary hierarchies into a sequence in which at least one of the transition audio segments is between sequential ones of the audio summaries; and rendering the sequence.