With iOS 4 for iPhone and iPad came third-party app multitasking. In addition to third-party applications, some of the iPhone’s built in native apps got some improved features as well. One of the hidden changes in iOS 4.2 is the ability to play the audio track from a video while performing other tasks on the iPhone.
Meaning, if you were watching a video (such as a video podcast) and need to check email on your device, you can do so while still listening to the audio from the currently playing movie, etc.
Open the iPod application on your iPhone or iPad. This app may also be placed in a folder if you have trouble finding it.
Once the iPod app is open, click on the Video tab in the bottom right-hand corner.
Navigate to a video you would like to play and tap it to begin viewing.
Once the video has begun playing, tap the home button to bring yourself back to the main screen of the phone. The audio will stop.
From the home screen, double-tap the home button to bring up the multitasking bar. From here you can swipe left or right to navigate your most recently used apps.
Swipe the multitasking bar to the left. This will reveal the iPod playback controls. Tap the Play button to begin playing the audio stream without going back to the video. You can now use the phone as usual without the background audio stopping when you reach another application.