Missing documentation: Describing Audio Sources or Other Media

[riedde]

Description needed for the guidelines:

• <captureMode/>
• <carrierForm/>
• <perfDuration/>
• <fileChar/>
• <playingSpeed/>
• <soundChan/>
• <specRepro/>
• <trackConfig/>

[KristinaRichts]

This issue is being processed as part of the MEI/AV extension in NFDI4Culture TA2 M3