SUMMARY Fading a video clip in and out will not start to reveal the clip below. STEPS TO REPRODUCE 1. Stack to video clips above each other (V1 and V2). The Clip in V1 should be a bit longer 2. Let the clip in V2 "Fade in" and "Fade out" by dragging the left/right upper corner of the clip towards the middle 3. Render this project OBSERVED RESULT In the rendered output movie: During the fading of the clip in V2 there will only a black nothing instead of the clip in V1 below be shown. As soon as V2 is fade out completely V1 will be visible abruptly by 100%. This is not what the project monitor shows during real time playback (it handles the fading correctly). EXPECTED RESULT The rendered output should be the same as the outout of the project monitor during playback within Kdenlive: The clip in V1 should shimmer through when the clip in V2 is faded. SOFTWARE/OS VERSIONS Linux: Arch/Kernel 5.12.1 KDE Plasma Version: 5.21.5 KDE Frameworks Version: 5.82.0 Qt Version: 5.15.2 MLT Version: 6.26.1 ADDITIONAL INFORMATION Problem occurs in Kdenlive 21.07.70 from git. And in 21.04.0 (official Arch Linux package). Tested with AMD ZEN Hardware + free Mesa Graphics AMD Stack. And on Intel/Nvidia proprietary graphics stack. Bug does not occur in Kdenlive 20.12.3 .
I tested with 1080p50 clips and rendered with CPU to MP4. It works as expected. What type of clip do you have and which render profile do you use? Please try without GPU rendering and if this is still not working check with the AppImage to see if there are packaging issues.
Sry - I didn't find this bug report of mine anywhere and then I opened it with another bug-id - it's already solved. I'll close this after this comment. In short: Arch Linux ships mlt v.7 as well as mlt v.6. Despite what the Kdenlive "about" dialog was claiming (mlt v.6) and what was set as mlt binary within the settings dialog (/usr/bin/mlt6) it used /usr/bin/mlt which happens to be mlt v.7 . And mlt v.7 has some internal changes and is not fully compatible with v.6. The current stable Kdenlive version needs mlt v.6, After removing the mlt v.7 package (and keeping mlt v.6) it all worked fine.
Thank you for the quick reply.