RE: audio/video workstation...
Hi zxspectrum,
I just wanted to add my two cents of experience before you buy...if you don't mind.
You state that your "main uses" are multi-track recording and Handbrake transcoding. For the Handbrake transcoding, the processor speed is irrelevant, in my opinion, since it is not a realtime event and you can just set up a batch process in Handbrake and let multiple videos be transcoded overnight. It doesn't matter, in other words, whether it takes 5 hours or 5.5 hours to transcode all of your 1080p videos, in the morning they will be done.
On the other hand, the multi-track audio and video recording is a realtime event, and for this the speed of the CPU does matter. If the CPU is not fast enough (or the Firewire/USB interfaces are not fast enough) and hiccups, then you won't be able to do your multi-track audio and video recording. (Yes, I'm assuming that the 1080p videos you're transcoding are ones you're also recording.)
In the last month, I have made about 15 hours of 1080p/30fps videos along with simultaneous 3- or 4-channel (3 or 4 microphones, depending up the precise recording setup) audio recordings all controlled and recorded on a 2.7GHz quad core i7 machine. These recordings were made with either an Avid/M-Audio or Focusrite interface (I tried both) and a Canon camera for the video. The laptop controls both the camera as well as the audio interfaces remotely. I have found that this setup taxes the rMBP fairly well, both in terms of CPU as well as the interfaces. I have experienced one hiccup (either the CPU or the USB interface did not "keep up" at one point) during these 15 hours of recording, requiring that one video had to be redone.
Also, you should know that GarageBand switches from the integrated GPU to the discrete GPU of the rMBP -- I don't know why GarageBand does this, that is, whether it actually uses OpenGL to offload some of the computational work to the GPU or not, but since GarageBand does cause a switch from integrated to discrete graphics it very well might. The temperature of my GPU does rise while I'm making these recordings, so I suspect it is being used to do some of the computations (although I don't know whether the GPU is simply doing the display computations for the GarageBand interface or if it is being called upon to also perform some of the computations for the audio).
In conclusion, I would be careful buying the 13" rMBP with its dual core i5 and without a discrete GPU, if indeed your plans are to do realtime multi-track audio and video recordings. If funds are a concern, you might then consider a cMBP with quad core i7 and discrete GPU as a way to save some money, especially since for your stated purposes you do not require the Retina display of the rMBPs. Another option might be to use two separate computers, one for the video and one for the audio, to lessen the computational requirements for any one machine.
...just a little free advice, the quality of which is exactly what you pay for it...i.e., none.
Regards,
Switon
P.S. Before the rMBP, I used to use a 2011 cMBP 2.4GHz quad core i7 with discrete Radeon GPU to perform similar audio/video recordings. I found that these recordings heavily taxed the cMBP, and I experienced more "hiccups" with the cMBP than I have with the rMBP, thus in my experience the faster machine made these recordings easier.
