https://bugs.kde.org/show_bug.cgi?id=476659
Bug ID: 476659 Summary: Rendering a Reversed Clip is Extremely Slow Classification: Applications Product: kdenlive Version: 22.08.2 Platform: Microsoft Windows OS: Microsoft Windows Status: REPORTED Severity: normal Priority: NOR Component: Video Display & Export Assignee: j...@kdenlive.org Reporter: bugs....@boffinbrain.com Target Milestone: --- SUMMARY When rendering a video that has a reversed clip, the reversed portion of the video takes an extremely long time. I understand that most codecs are designed under the assumption that videos are played in a forward direction and thus i-frames depend on the preceding frames, thus a lot of seeking is necessary if frames are requested in reverse order. However, in my testing I found that rendering regular video could be around 30fps while the reversed section would be approximately 0.5fps. Surely there are some optimizations we can make to this process, and perhaps they can be applied to within the editor too for faster playback. STEPS TO REPRODUCE 1. Add a clip to the timeline (recommended at least 5 seconds long) that's an MP4 video or similar. 2. Make a copy of it, place it after the first clip and reverse the clip. 3. Start rendering the project. OBSERVED RESULT Rendering the first half of the video is fast, while the second half is *extremely* slow. EXPECTED RESULT Speed for rendering the second half should ideally be within the same order of magnitude as the first half. SOFTWARE/OS VERSIONS Tested on Kdenlive 22.08.1 and 22.08.2 Windows 10 KDE Frameworks Version 5.110.0 Qt Version 5.15.10 (built against 5.15.10) -- You are receiving this mail because: You are watching all bug changes.