I'm sure others have noticed the many differences between Airport Express and AppleTV... not merely the obvious addition of video bridging. The concept is somewhat the same... media bridge. But there does seem to be some marked differences in terms of resources usage and operation.
Basically, the resources usage on the host computer is next to nothing with at least music. I haven't yet observed the resources usage with video. I've also noticed that wireless bandwidth usage is more efficient.
One problem with Airport Express was that most of my operation consisted of using the laptop in the living room as a user interface, even to access the library on my G4 in the office right behind the living room via music sharing... but you can see the problem here. I've got some wireless bandwidth eaten up talking to the computer in the office, some wireless bandwidth eaten up by the computer in the office talking back to the laptop, and then more wireless bandwidth AND CPU and drive resources on BOTH machines being eaten up transmitting music sharing-accessed material to the Airport Express... and doing so with iTunes actively "playing" the shared file through the front end of the laptop.
But in this case with AppleTV... It appears to be talking only to the backend database of iTunes, using the front end active application only as a gateway to connect to that backend. Network traffic from this laptop remains fairly constant between 14-18 kilobytes/sec (112-144 Kbps) when streaming music. Barely any overhead traffic, if at all.
When streaming from a host computer, Activity Monitor shows iTunes using 0.30% of my RAM (512MB on this laptop). Playing the file in iTunes, as you would through to Airport Express, increases memory usage on the host computer to nearly 20%.
Additionally, the drive usage is somewhat different. In one instance, playing the file in the iTunes interface on the computer the entire file seemed to be read into memory from the drive in one large burst. While streaming to iTunes, reads from the hard drive occur in regular intervals at about 120-200 kilobytes per second ratewise... but hardly a fraction of a second in each instance. I assume it's bursting a segment to the AppleTV buffer and then bursting the next segment as the AppleTV memory buffer runs down. Airport Express seems to lock up occasionally, as if there are buffer underrun problems. Again, could also be a much poorer antenna reception on the Airport Express vs. the AppleTV (which gets full signal in an area of my living room where AppleTV would not stay connected for long). Let me add I live in an apartment high-rise where the walls are framed with steel and floors are separated with concrete, but there are also a number of nearby wireless base stations that would frequently interfere with the Airport Express signal as well as my Powerbook G4/1GHz laptop which has the aluminum-encased antenna (the Macbook fixed this with a plastic/rubber edge that didn't inhibit the signal nearly as much).
Another thing... I could be wrong but I seem to recall something about AirTunes resampling every format to 320Kbps *before* streaming to Airport Express... but here it looks like 128Kbps AAC is streamed at 128Kbps based on the average of the aforementioned range. My guess from the specs, though I haven't tested this yet... is that higher bitrates are downsampled to the max cap of 320Kbps AAC for transmission to AppleTV.
There could be various factors involved here... but I'd like to hear other people's observations regarding those factors. It appears, for one thing, that the front end of iTunes isn't active at all on the host streaming computer... it lies dormant like a gateway, to allow AppleTV to talk to its backend database, taxing at most the hard drive of the host computer.
Basically, the resources usage on the host computer is next to nothing with at least music. I haven't yet observed the resources usage with video. I've also noticed that wireless bandwidth usage is more efficient.
One problem with Airport Express was that most of my operation consisted of using the laptop in the living room as a user interface, even to access the library on my G4 in the office right behind the living room via music sharing... but you can see the problem here. I've got some wireless bandwidth eaten up talking to the computer in the office, some wireless bandwidth eaten up by the computer in the office talking back to the laptop, and then more wireless bandwidth AND CPU and drive resources on BOTH machines being eaten up transmitting music sharing-accessed material to the Airport Express... and doing so with iTunes actively "playing" the shared file through the front end of the laptop.
But in this case with AppleTV... It appears to be talking only to the backend database of iTunes, using the front end active application only as a gateway to connect to that backend. Network traffic from this laptop remains fairly constant between 14-18 kilobytes/sec (112-144 Kbps) when streaming music. Barely any overhead traffic, if at all.
When streaming from a host computer, Activity Monitor shows iTunes using 0.30% of my RAM (512MB on this laptop). Playing the file in iTunes, as you would through to Airport Express, increases memory usage on the host computer to nearly 20%.
Additionally, the drive usage is somewhat different. In one instance, playing the file in the iTunes interface on the computer the entire file seemed to be read into memory from the drive in one large burst. While streaming to iTunes, reads from the hard drive occur in regular intervals at about 120-200 kilobytes per second ratewise... but hardly a fraction of a second in each instance. I assume it's bursting a segment to the AppleTV buffer and then bursting the next segment as the AppleTV memory buffer runs down. Airport Express seems to lock up occasionally, as if there are buffer underrun problems. Again, could also be a much poorer antenna reception on the Airport Express vs. the AppleTV (which gets full signal in an area of my living room where AppleTV would not stay connected for long). Let me add I live in an apartment high-rise where the walls are framed with steel and floors are separated with concrete, but there are also a number of nearby wireless base stations that would frequently interfere with the Airport Express signal as well as my Powerbook G4/1GHz laptop which has the aluminum-encased antenna (the Macbook fixed this with a plastic/rubber edge that didn't inhibit the signal nearly as much).
Another thing... I could be wrong but I seem to recall something about AirTunes resampling every format to 320Kbps *before* streaming to Airport Express... but here it looks like 128Kbps AAC is streamed at 128Kbps based on the average of the aforementioned range. My guess from the specs, though I haven't tested this yet... is that higher bitrates are downsampled to the max cap of 320Kbps AAC for transmission to AppleTV.
There could be various factors involved here... but I'd like to hear other people's observations regarding those factors. It appears, for one thing, that the front end of iTunes isn't active at all on the host streaming computer... it lies dormant like a gateway, to allow AppleTV to talk to its backend database, taxing at most the hard drive of the host computer.
