Jason Tomczak

Suffering from Irritable Buffer Syndrome?

After writing a glowing review of Apple’s AirPort Extreme (glowing review well deserved), I received a few emails from folks inquiring about using the AirPort Extreme to stream their iTunes music libraries. I posted some images and information about this - the most significant bit of data being the average 33KB/s (264kbps) bandwidth used for streaming audio.


A couple days ago, I got another email from an observant Mac user (Chris W) who was experiencing some trouble playing video files from his USB hard drive attached to AirPort Extreme base station. Video playback was jerky and sound intermittently cut out.


I tested the same scenario - using the AirPort Extreme to stream video to my MacBook Pro. This is essentially the identical task of the upcoming AppleTV.


Although the AppleTV may employ secret magic or buffering tech that I am not aware of, streaming video between the AirPort Disk and a wireless computer should give a close approximation of how the AppleTV streaming would perform. The AppleTV also sync’s video, photos and audio with up to 5 wireless computers so content can be viewed without the need for streaming. Of course, with a tiny 40GB hard drive, the AppleTV may quickly fill up, requiring all additional content to stream.


There are essentially two popular/likely protocols that will be used between the AppleTV, the AirPort Extreme and a home user’s computer. 802.11b/g is the most common protocol due to the scarce number of people in early 2007 who are actively using the next-gen 802.11n.


With the AirPort Extreme, 802.11b/g data transfer rates, as explained in an earlier review, average about 1.7MB/s (13,926kbps), with an occasional average of 3.4MB/s (27,852kbps) depending on site conditions. 802.11n rates were much better - 6.2MB/s (50,790kbps).


As demonstrated in the two screen captures below (thanks to iShowU) the bandwidth required to stream video is much greater than streaming audio. Again, audio averaged 33KB/s, whereas video averages anywhere from 100KB/s to 400KB/s (800-3,200kbps). In separate tests with AVI files, I’ve seen the transfer rates ranging between 500KB/s and 1.2MB/s (4,000kbps-9,830kbps).


The two clips below are both 40 second clips that start out at the exact same point in the video. Due to inadequate streaming and buffering in 802.11b/g mode, the video stalls repeatedly, thus causing the 40 second end-mark to fall on a different scene.


AirPort Extreme video 802.11b/g - herky jerky

AirPort Extreme video 802.11n - silky smooth




Again, it looks like video streaming takes anywhere from 3 to 35 times as much bandwidth as streaming audio depending on the size of the video file, the file type (h.264 vs. avi vs. mov, etc.). I’ve taken a couple stills to show the bit rates of tested movies. They are:


Movie Purchased via iTunes




Legal Backup of Owned DVD




While discussing this issue with one of my uber-geek friends, he suggested that the bit rate of the backed-up DVD may be higher than that of iTunes movies and that iTunes movies would probably play better via 802.11b/g. The images above show that the iTunes movie has a higher bit rate.


The 802.11b/g protocol on the AirPort Extreme just can’t seem to handle video smoothly without supplemental buffering or caching. 802.11n, however, plays video flawlessly. It’s really just as good as if it was being played directly from an internal hard drive or from a DVD.


Of course, I’m not part of Apple’s R&D team so I can’t confirm if this video playback issue has anything to do with why the AppleTV was delayed. If anything, it’s something that Apple should be aware of. Knowing Apple, they probably are aware of it and I’d bet good money that they’ve got a fix for it - maybe a nice big fat buffer built into the AppleTV - enough to prevent Irritable Buffer Syndrome. What a pain in the butt that could be.


Some folks out there may say I’m way off the mark. I don’t know. They could be right. The current speculation is that Apple has delayed the AppleTV as a marketing ploy. Which seems more logical? While I could be wrong, it seems better to delay the launch while figuring out how to improve streaming & caching issues than to release a product that could potentially become an embarrassment.


Either that, or it really is just a tricky marketing ploy.

NB: The screen captures used above were used with a legally backed-up copy of one of my favorite home-library DVDs, The Professional, starring Jean Reno, Gary Oldman, Natalie Portman and Danny Aiello.

Stumble it!

Tags: Apple TV, Mac