Audio Streaming API Guide

Best Practices

Sending audio data

The audio source should not use session ID 0 to broadcast the Data signal; it should send Data signals on each AudioSink's session.

NOTE: Care should be taken when specifying the amount of data to send in each signal so as not to interrupt the delivery of audio data.

Clock synchronization

The maximum error of the clock synchronization algorithm defined in the Audio Interface Definition is the value used in the AdjustTime step. The algorithm may be repeated to bind the maximum error.

UI considerations

Button to list Sinks in proximity

To provide the best experience for a consumer using an application that allows for streaming audio to applications/devices running the Audio service framework, configure the application to let the consumer select the Sinks to stream to. It is entirely possible to play audio on any Sink found, but this may not be the best option for a user.

The Android sample includes a button that a user can select to list nearby Sinks. These Sinks can be selected/deselected as desired by the user. The list is populated via the SinkFound callback. The button should only appear if there is a Sink in proximity.

The appearance of a button allows the user of the application to recognize that the application supports the Audio service framework.

Button to refresh list of Sinks

There are times, due to UDP propagation delays, when a Sink is not displayed right away. Providing the user with a button to refresh the list is an easy way to empower the user with the ability to start searching for Sinks again.

When the Refresh button is pressed, make a call into your SinkSearcher object to call the Refresh() method. When doing this, the list that is displayed should be cleared and, as the SinkSearcher responds with SinkFound callbacks, the list is populated again.

Refer to the Audio service framework APIs for more information about SinkSearcher::Refresh().

When to add a Sink

While it's possible to place the AddSink call when a Sink is found, it is not recommended. A button should be present to let the consumer control where the audio from the device is being sent.

Handle losing a Sink

If a SinkLost callback occurs and audio is not being played, remove the line item representing the lost Sink. There is no reason to alert a consumer, and it does not impact the user experience.

If audio is being played on a single Sink and SinkLost or SinkRemoved occurs, a pop-up should appear that gives the user the option to continue playing locally or refresh to find other sinks. See When to add a Sink.

When playing to multiple Sinks, the audio should continue on the other connected Sinks. A popup should appear that informs the user that a Sink has disappeared and include the name of the Sink. This allows the user to investigate the cause. Some possible causes include:

  • The Sink has powered off.
  • Another application is now using the Sink.
  • The Sink is no longer in proximity.

Play multiple audio formats

The Audio service framework supports PCM data over the wire. (The current release does not support sending compressed audio.)

To provide the best user experience when displaying the list of songs on the devices, consider filtering the list in advance to avoid playback issues.

  • If the application is intended to run on devices running Android versions earlier than 4.0 (Ice Cream Sandwich, ICS), the developer must decode the MP3 file.
  • If the application is intended to run on ICS, use the Android OpenSL ES APIs to decode audio formats into 16-bit 44.1 kHz or 48 kHz.

See the Audio API Guide for instructions on writing a custom DataSource implementation.