Going Mobile: Streaming to Mobile Devices

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The challenges of streaming audio to mobile devices and moving vehicles

This month we revisit the topic of streaming audio to mobile devices - with an emphasis on vehicles. What does it take to stream audio into a car "radio?"

Unlike over-the-air transmission (with a single standard of 75kHz deviation, and 75µs pre-emphasis), there are multiple ways to stream to mobile devices, and the data rate depends on the device's network. Table 1 provides some insight.

Phone typeProtocolCodecData rate
iPhoneHTTPMP4 (AAC)64 or 40kb/s
BlackberryHTTPMP4 (AAC)64 or 40kb/s
AndroidRTSPMP4 (AAC)32kb/s
Flash encoderRTMPMP4 (AAC)64 or 32kb/s
Table 1. Various data rates and protocols for mobile devices.

The bottom line is that you will have at least one and perhaps more computers generating streams targeted for the different platforms out there. More on that a little later.

With respect to a particular platform, you will work with an application developer in determining the protocol (such as HTTP or RTSP [or RTMP if using Adobe Flash]). You will chose the data rate likely in conjunction with the network provider and network type (i.e., UMTS or CDMA2000 [EV-DO]). You will chose the lossy codec (such as AAC) based on what you want the stream to sound like to the end user. Once you come up with those specifications, the app developer will build the app around those basic parameters. And speaking of applications developers, very few broadcasting companies have the wherewithal to have their own in-house; that's where a company such as Airkast comes in to the picture. Its product called TuneKast is specifically for broadcasters; think of it as a turnkey solution that encompasses necessary applications, trafficked ad-insertion, title and artist displays, and finally distribution via CDN.

StreamOn is another provider of streaming services. It provides a small appliance (running on Unix) to the radio station that encodes the audio in AAC+, Ogg Vorbis and in some cases MP3. This appliance then sends the stream outbound for subsequent distribution to end users. If the radio station provides the appropriate metadata, then the StreamOn player will show title and artist information. StreamOn can also build custom iPhone apps, or integrate with existing third-party apps. Perhaps most importantly, StreamOn offers Ad Tools, which is a way to generate revenue from the streaming content.

Liquid Compass also offers custom apps for mobile phones in addition to their support of desktop players. Some of the features it offers: now-playing (of course); social media integration; on-demand access to local weather and news; and finally a favorites repository for the end user, along with music history. Naturally, it offers a means by which ad-insertion can be done as well through a partnership with AdsWizz.

- continued on page 2

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