After having finished the first batch and have had to work on other projects, I received an email about the upcoming batches which they want stored in a digital form. This digital copy will from then on be the "new original" and since this is for a national library, the final material ought to have as much detail/information left as possible.

What format would be most suitable to capture and store the material in?
The Matrox RT.X2 SD can capture in the following formats:

• Matrox MPEG-2-I-frame 4:2:2
• Matrox DV/DVCAM
• Matrox DVCPRO

There are only settings available to change when capturing to MPEG. I can then set the data-rate (25Mb/sec max), rounding type (MPEG2 or Matrox custom), zig-zag order (regular or alternate), DC-precision (8-11 bit) and finally I can force frame-based DCT.

Audio-wise I capture to wav (16-bit/48KHz, unable to capture 24-bit).

So, what format would be the best alternative for capturing and then long time storing of the material?

We are still dealing with VHS material and older.

DVCPRO50 would have been an ideal choice, with its 4:2:2, but alas that is not available.

If this is PAL material, Matrox DV (DV25) would work, with its 4:2:0.

If NTSC, I worry about the 4:1:1 colorspace compression, I don't consider DV25 archival.

In theory, 4:1:1 is supposed to be better for degradation in latter generations of the content, but I find it isn't so when dealing with VHS sources. The reds and greens have been shown time and again to act oddly downconverted to 4:1:1 -- colors can feel "cooked" at times -- behaving a bit better in 4:2:0. Video shot DV seems to follow the theory, video converted to it -- not so much.

If you want to do the 4:1:1, then do DVCPRO (DVCPRO25) for both PAL and NTSC sources.

Honestly, MPEG-2 I-frame only DC10 @ 20Mbps could be acceptable too. At least 15Mbps, 20Mbps may help, 25Mbps may just be overkill and padding filesize. These would not be MP@ML encodes like you do for DVD-Video (max bitrate 15Mbps), these are going to be MP@HL or HP@HL.

Note that the "hobby crowd" has been spoonfed anti-MPEG information for years now -- info that MPEG is "not archival" -- but it was geared more at their low-end high-compression methods. But even studios are known to store videos in I-frame or even custom IP-frame MPEG-2 at high bitrates. And there is, of course, the obvious difference between consumer tools (DVD recorders) and professional tools (NLE cards).

My personal choice would be for the PAL DV (DV25). Ask a dozen people, and you'll likely get a dozen preferences. You're already limited to three good choices. Each of them is lightly compressed intra-frame (not inter-frame) with differing colorspace compressions. There really isn't a "best" here, each of them has its own quirk.