MPEG-4 Audio Properties

While Yate extracts the audio properties of AAC and ALAC files with a high degree of accuracy, MP4 files may employ far more complicated mechanisms to describe the audio properties of different stream types. Yate does not directly have the ability to extract the audio properties for all possible formats. While this in no way affects the tagging of the file it can affect the display of the audio property information. Yate has the means to extract and retain the audio properties via an additional component. This additional component should have been automatically installed. You can always manually install the required component via Yate>Setup>Install Additional Components. If you do not have web access on the Mac running Yate, read the Manually Installing Required Components topic.

Settings - Audio Files - MPEG-4 has Retain audio properties settings which allow you how to control the automatic importing of the properties to be retained and how the properties are read. The read setting will be automatically set to its typical usage whenever the write setting is changed. The properties are retained so that they do not have to be extracted each time a file is loaded.

Yate supports the reading of retained audio properties in two possible locations: a UDTI named Retained Audio Properties and an extended file attribute. You can separately set how retained properties are written and read. You will be notified if a setting combination is invalid or makes no sense.

When reading an MPEG-4 file, the following workflow is employed:

• If a Retained Audio Properties UDTI is available and the read setting is Read UDTI or Read Both, it will be used to preset the audio properties, otherwise Yate will attempt to directly read the properties. Currently Yate can directly extract the properties for AAC, ALAC and E-AC-3 streams.
  
  
• If issues are detected with the properties, an attempt is made to read the properties from an extended file attribute. This is only done if the read setting is Read Xattr or Read Both.
  
  
• If there are still issues with the properties and the Retain audio properties write setting is not Never Write, an attempt will be made to extract the properties from the additional component. If the properties can be extracted:
  
  
  • If the write setting is Write UDTI, the retained properties are saved to a Retained Audio Properties UDTI. When the UDTI is first created, the audio file will load as changed. ie. a red change indicator will be visible. In order to retain the properties, the file must be saved.
    
    
  • If the write setting is Write Xattr, the properties are saved as an extended attribute on the file.

Both methods of retention, effectively operate the same. The Write UDTI method, uses a tag in a file and as such the file must be saved. The Write Xattr method does not require the file to be saved but it does require a file access to extract the extended attribute. Further, extended attributes will not work on all external drives.

You can check for the presense of the extended attribute by examining the Xattrs property in the Snapshot Editor. If the extended attribute exists, the Xattrs property will contain a P.

The read setting will typically match the write setting. Full granularity is provided so that the write can be disabled but preexisting values can still be read.

The extended attribute can be removed via File>File Maintenance... and by the same named action statement. More information can be found here.