It would appear the Media Express capture program is not DirectShow based.
This would make sense as Blackmagic makes a version for other platforms. It appears to use the QT user interface library which is also cross platform.
A best guess would be like VLC, they use a libavcodec or a wrapper like ff to use libavcodec.. but I'm betting they had to keep it simple. There is an LGPG notice included with the program that might refer to the QT libraries used.. or deeper in the code. I did not see a separate libavcodec dll included with the program, so if it is used.. its function are integrated with Media Express binary as a static compile. It is a medium sized executable. dedicated to one purpose.
The weak link in all of my captures has been Uncompressed at 8 and 10 bit resolution direct to hard disk.
Media Express does a good job of capture and maintains sync as far as I have tested.. but my hard drive speed is borderline and would probably not keep up long term.
VLC so far has not been able to keep up and appears to loose sync between the audio and video tracks when captured with the default Raw Record button. Adding a Transcoder to capture as MPEG2 or H.264 would seem to be a loosing proposition.. but might work, if the CPU is not overloaded and can reduce the stream speed such that the hard disk can keep up. Huffyuv is also possible with VLC and might make a reasonable compromise. -- noted that VLC is also capable of decoding and playing back Huffyuv on the fly! Which is quite impressive.
The Blackmagic Intensity Extreme is about ten years old, and in those days the limitations were as now the hard disk speed, in fact they include tools to test the speed.. and recommendations of always using a RAID0 situation to stripe the speed load across multiple disks. Today SSD might be able to keep up, but the individual SATA drive connections may still be too slow.
Noel's AMCap for Windows XP is no longer sold.. however due to his kind response to a plea for help, he did sell me a copy.. and that does appear to work excellently with the Blackmagic Intensity Extreme on the Windows XP laptop across the Thunderbolt connection.
Noel's AMCap for Windows now focuses on 64 bit versions of Windows and more modern versions of the Windows Kernels.. and had to leave Windows XP compatibility behind with the Version 9 of AMCap.
VirtualDub 1.9.11 does a respectable job of capture, but I am concerned compared to Media Express, or even VLC.. its a rather Large and Excessive program just for capture.. it has measures to try and help with hard disk speed like preallocation and buffers.. and logic for dealing with hard disk overruns.. but they are kind of overwhelming to master right away. But it does a good job from what I can see.