Windows 7 X64, AMD Radeon HD 5800
Short description of error
Audio in some video container formats is not properly decoded, resulting in silence during editing (and also rendering) when using the video sequence editor. The failure pertains to MP4 files in my testing; the audio codec is reported by gspot as "mp4a: MPEG-4 AAC LC".
Other container formats do work; wmv is properly decoded, for example.
My test video was encoded by Lumia 1020 video camera app.
Exact steps for others to reproduce the error
Import a MP4 file as a pair of strips (audio and video) to the video sequence editor, and observe silence. Rendered audio is also silent.