Bug 486056

SUMMARY
The "2 pass" checkbox is never selectable for formats such as H264 and H265 where it should theoretically be available depending on the rate control setting.

STEPS TO REPRODUCE
1. Create a render preset for the libx264 codec with "CBR - Constant Bitrate" or "Average Bitrate" rate control.

OBSERVED RESULT
2. Observe the "2 Pass" checkbox is greyed out in the main render dialog.
3. Edit the preset again, add "passes=2" to the "Additional Parameters:" box in the "Other" tab, and observe that the checkbox becomes checked (and is no longer greyed out).

EXPECTED RESULT
The "2 Pass" checkbox should be selectable in cases where it's possible to use it. Checking or un-checking the box should add/remove the text parameter; it shouldn't be necessary to manually change the text parameter in order to control the checkbox.

Given the number of questions I've seen about this checkbox on places like the /r/Linux and /r/Kdenlive subreddits, it might be useful to also include a tooltip broadly explaining when it is/isn't available when the checkbox is greyed out for an actual reason.

SOFTWARE/OS VERSIONS
Linux/KDE Plasma: Kernel 6.8.7-arch1-1 / Plasma 6.0.4
KDE Plasma Version: 6.0.4
KDE Frameworks Version: 6.1.0
Qt Version: 6.7.0

ADDITIONAL INFORMATION
I don't think this is a very recent regression, but I don't have time to bisect right now.