User guide

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AVAudioSessionCategoryMultiRoute—Playback and record. Allow simultaneous input and output

for different audio streams, for example, USB and headphone output. A DJ app would benefit from using

the multiroute category. A DJ often needs to listen to one track of music while another track is playing.

Using the multiroute category, a DJ app can play future tracks through the headphones while the current

track is played for the dancers.

Expanding Options Using the Multiroute Category

The multiroute category works slightly differently than the other categories. All categories follow the “last in

wins” rule, where the last device plugged into an input or output route is the dominant device. However, the

multiroute category enables the app to use all of the connected output ports instead of only the last-in port.

For example, if you are listening to audio through the HDMI output route and plug in a set of headphones,

the audio plays through the headphones. Your app can continue playing audio through the HDMI output route

while also playing audio through the headphones.

Working with Categories

Expanding Options Using the Multiroute Category