I am using the Tencoder portable app, (installed on a thumb drive) and got the following message while trying a dvd rip
Assertion v>0 && v
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Tencoder error
December 8, 2018 - 3:54pm
#1
Tencoder error
December 8, 2018 - 4:31pm
#2
No longer developed
TEncoder has not received any updates for 3 years, so you may be running into a DRM issue, I ran into a different DRM-related issue when I attempted a DVD rip to confirm your problem.
Please try using the installed version, to ensure the problem is not with TEncoder itself.