iPhone HE-AAC Streaming over Mobile Network (3G)

Question

Developed an internet radio streamer using jPlayer which utilizes the html5 audio tags with jQuery and has a flash fall back for unsupported browsers. Upon testing the player on the iPhone (iOS 5.0.1), we ran into a very peculiar issue.

When the iPhone is connected to WiFi, it streams perfectly using the HE-AAC V2 stream @ 64kbps 44.1kHz (the preferred codec for apple products). However, when the iPhone is connected to the 3G mobile network, it "stutters" or stops streaming for 1-2 secs every 1-2 minutes (does not stop streaming completely). The troubling thing is when the iPhone is forced to use a separate MP3 stream at the same bit rate, it does not have this issue and works very well on 3G.

UPDATE 5

We recently acquired a 3G/4G Sprint mobile hotspot device and tested this issue with the device. When the iPhone is connected to the mobile hotspot, it shows as being connected to a wifi device and the issue does not render even tho the actual connection is via 3G/4G. This might point back to the issue being with the iPhone not handling HE-AAC via HTTP Live Streaming and when directly connected to the mobile network.

UPDATE 4

Updated the iPhone to iOS 5.1 yet the issue persists.

UPDATE 3

Read here on SO various issues of script not rendering correctly when connected to mobile networks. The finger seems to point to the mobile network carriers that may be inserting Proxy to serve webpages, eg for downsizing images. Also it might inject some JavaScript pages. The test page can be found HERE Note: this page is using HE-AAC so it will only work on iPhone...

UPDATE

According to Apple's HTTP Live Streaming doc for iOS devices, that "Audio-only content can be either MPEG-2 transport or MPEG elementary audio streams, either in AAC format with ADTS headers or in MP3 format." Our music server is using OddcastV3 encoder to send out three streams (MP3, HE-AAC V2, and Oggvorbis) to the icecastV2 server. Not sure if the encoder is inserting ADTS headers for the HE-AAC V2 stream. Is there a way to check for this?

Answer 1

Comming from a radio planning point of view - here are my two cents:

What you are describing sounds like bandwidth shaping - which is both a common and often neccesary design of radio networks (like 3G networks). In most 3G operators I worked at you would typically optimize your network to give high-speed burst (think downloading an image, sending one email or fetching one HTML page) - over "long-running" high bandwidth services. This is due to the simple fact that this is what most users want/need.

This shaping can on a typical 3GPP (GSM 3G) network result in that you will first get a RAB (radio access bearer) supporting 384kbit and is then downgraded as long as your your device accepts it. This means that typicall you will get switched from 384 -> 256 -> 128, then 64kbit where maybe your device starts recieving data to slowly, then the network upgrades it and again downgrade it after a while.

So why is not then the MP3 file stuttering? my guess is that the total kbit rate might differ - so you are fine in the 64kbit RAB. This is a common phenomena.

Answer 2

We have managed to get the exact same thing working. 64kbit AAC-v2 on mobile devices. We are streaming files and not a steady stream, I think Magnus is right when he explains how the network prioritized traffic to bursts, in our case that means we have large parts of the file right away and the player can continue to play until he next burst comes in. In your case that means the stream pauses until the next burst comes.

Either if you can switch to larger chunks in your streaming (larger buffer) or stream whole files instead?

We had a very strange phenomenon with iOS, we had to rename all files from .m4a to .aac to be able to get them streaming on iOS. If we didn't rename them iOS wouldnt play them.

Good luck.