Video freezing in Recording View

[FolkHistory]

Video all looks fine in Passthrough View (and when capturing with Media Express) but in Recording View is freezing every few seconds then speeding up to correct itself. I've tried all sorts of tests, upgrading, reinstalling etc. but am still stuck.

I'm getting these messages in the terminal log by the way

[v210 @ 0x7fb1ef705100] Application has requested 33 threads. Using a thread count greater than 16 is not recommended.
[Parsed_amovie_0 @ 0x7fb1f01061c0] Channel layout is not set in output stream 1, guessed channel layout is '7.1'

Could be relevant? Any suggestions?

Thanks! Nigel

[FolkHistory]

Just adding some specs to this:

• Mac Pro 2019 running Sonoma 14.4.1

• Black Magic Desktop Video vers 12.9

• BM Hardware - Ultrastudio 4K Extreme and Ultrastudio HD Mini (same issue with both)

• I am capturing VHS PAL via Leitch DPS-575 SDI out File format Matroska FFV1 vers 3, 24 bit PCM QC Tools XML after recording

Video freezes in all of these views : Unfiltered, Visual, Audio + Video, Visual + Numerical (thought testing 4 was enough for now)

Also, if I run Vrecord with QC Tools XML set to concurrent, capture fails and I get the following errors as part of the log

[Parsed_amovie_0 @ 0x7fc094f04840] Channel layout is not set in output stream 1, guessed channel layout is '7.1'
    nan    :  0.000 fd=   0 aq=    0KB vq=    0KB sq=    0B f=0/0   
analyzing input file... -
                                                   0 of 100 %[matroska,webm @ 0x7fc094f04fc0] File ended prematurely
[matroska,webm @ 0x7fc094f04fc0] Seek to desired resync point failed. Seeking to earliest point available instead.

QCTools analysis is complete.q=    0KB vq=    0KB sq=    0B f=0/0   
Checking file conformance against FFV1 video policy...   0B f=0/0   
[Parsed_amovie_0 @ 0x7fc094f04840] EOF timestamp not reliable=0/0   
    Last message repeated 1 times

Thanks, Nigel