How to Use the Command 'pw-metadata' (with examples)

The ‘pw-metadata’ command is a powerful tool for managing metadata in PipeWire, a server and user space API for managing multimedia pipelines. It allows users to monitor, set, and delete metadata associated with PipeWire objects. By understanding how to utilize ‘pw-metadata’, users can efficiently manage their multimedia environment through metadata manipulation. The versatility of ‘pw-metadata’ makes it invaluable for both developers and system administrators working with multimedia applications.

Use case 1: Show metadata in the default name

Code:

pw-metadata

Motivation:
Using pw-metadata without additional arguments provides a quick snapshot of the current default metadata on your PipeWire objects. This is particularly useful for system administrators or developers who need to verify configurations or diagnose issues with the default PipeWire setup.

Explanation:

• pw-metadata: This is the basic invocation of the command which, by default, displays metadata associated with the default name. No additional arguments are needed to achieve this.

Example output:

metadata {
  default.audio.sink = "alsa_output.pci-0000_00_1f.3.analog-stereo"
  default.video.source = "v4l2_input.pci-0000_00_14.0-usb-0:2.2:1.0"
}

Use case 2: Show metadata with ID 0 in settings

Code:

pw-metadata -n settings 0

Motivation:
This use case allows users to query the metadata for a specific object, identified by an ID within a specific category or namespace, in this case, settings. It is particularly useful when troubleshooting or validating current configurations tied to specific parts of the multimedia pipeline, such as audio or video settings.

Explanation:

• -n settings: This flag specifies the namespace, which in this case is settings. It tells pw-metadata where to look for the metadata.
• 0: This is the ID of the metadata object you want to view. IDs are used to uniquely identify different metadata objects.

Example output:

metadata {
  settings.volume.level = "0.8"
  settings.mute = "false"
}

Use case 3: List all available metadata objects

Code:

pw-metadata -l

Motivation:
Listing all available metadata objects provides a comprehensive overview of all current metadata entries within the PipeWire environment. This is crucial for users who need a full view of the system’s multimedia configuration or who are auditing the environment for redundant or conflicting metadata entries.

Explanation:

• -l: This flag stands for --list and instructs the command to display a list rather than a specific item’s metadata. It outputs all objects’ metadata currently available in the system.

Example output:

1 - settings
2 - default
3 - custom.object

Use case 4: Keep running and log the changes to the metadata

Code:

pw-metadata -m

Motivation:
Monitoring metadata in real-time is crucial for developers and administrators to observe changes as they happen. This is particularly useful in debugging situations or when live adjustments are made and need to be tracked for validation or logging purposes.

Explanation:

• -m: This stands for --monitor, which tells pw-metadata to keep running continuously, logging changes to metadata as they occur. This allows for real-time tracking.

Example output:

Metadata changed: default.audio.sink = "alsa_output.usb-Focusrite_Scarlett_2i2_USB"
Metadata changed: settings.volume.level = "0.75"

Use case 5: Delete all metadata

Code:

pw-metadata -d

Motivation:
Clearing all metadata is a drastic yet necessary action when resetting the multimedia configuration or troubleshooting significant issues caused by corrupted or conflicting metadata. It provides a clean slate, which can often resolve persistent configuration issues.

Explanation:

• -d: This flag stands for --delete and instructs the command to remove all metadata entries. This is a powerful option that should be used with caution as it clears all configurations.

Example output:

All metadata cleared successfully.

Use case 6: Set log.level to 1 in settings

Code:

pw-metadata --name settings 0 log.level 1

Motivation:
Setting specific metadata values is a common requirement for customizing multimedia behaviors. Adjusting the log.level within the settings namespace demonstrates fine-grained control of application or system logging behavior, vital for debugging or managing log verbosity.

Explanation:

• --name settings: Specifies the namespace to which the metadata belongs.
• 0: Indicates the ID of the metadata object to be modified.
• log.level: The metadata key that is being set.
• 1: The value to set for the log.level key, typically altering verbosity.

Example output:

Successfully set log.level to 1 in settings.

Use case 7: Display help

Code:

pw-metadata --help

Motivation:
Accessing help documentation directly from the command line is invaluable for users needing clarification on usage, flags, and options. It is a quick way to familiarize oneself with the command’s functionality without external resources.

Explanation:

• --help: This flag brings up the help documentation, which includes a summary of command options, flags, and descriptions for user guidance and support.

Example output:

Usage: pw-metadata [options] [command]
Options:
  -n, --name NAME            Use the given metadata name
  -l, --list                 List metadata objects
  -m, --monitor              Monitor metadata changes
  -d, --delete               Delete all metadata
  --help                     Show this help message

Conclusion:

Understanding and utilizing the ‘pw-metadata’ command with PipeWire can significantly enhance the management and customization of multimedia configurations. Each use case provides a practical scenario where specific flags and options can be applied, showcasing the versatility and utility of the command. From monitoring real-time changes to setting specific metadata values, mastering ‘pw-metadata’ is key in any multimedia setup leveraging PipeWire.