Created attachment 111460 [details] Videos encoded in different codecs with transparent background I am going to make motion graphics in Adobe After Effects or Apple Motion and use it in kdenlive. I have explored available export video formats, because I feel it more comfortable than image sequences. Some codecs are not transparent in Kdenlive timeline and one codec is not transparent in project bin clip icon. I have tested all available standard export codecs in Ae which support alpha (except DNxHD/DNxHR) and additionally I have installed TechSmith Screen Capture codec v1 in Windows. It also supports transparency and became available to export using it in Ae. In Motion I have tested ProRes 4444 and Animation (via Apple Compressor settings) codecs. Here is list of issues that I have found in format Container - Codec - What's wrong - ffmpeg supports alpha: Avi - tscc - bbg*, bbgpb* - probably not** QuickTime - GoPro CineForm - bbg - yes QuickTime - ProRes 4444 - bbg - yes * bbg - means black background in timeline when placing above some clip instead of transparent background * bbgpb - black bg in project bin in clip icon instead of transparent ** I have tested if ffmpeg itself supports transparency for the codec. I used a command like this: ffmpeg -i normal_video.mp4 -i motion_graphics_with_transparent_bg.mov -filter_complex "[0:v][1:v] overlay=25:25" -pix_fmt yuv420p -c:a copy output.mp4 It worked for both mentioned codecs in quicktime, but did not work for Avi-tscc. Maybe ffmpeg just do not support transparency for tscc? How can I know that for sure? Because I would prefer tscc over Quicktime-Animation, because it compresses file size much-much better. Sample videos encoded with problematic codecs are attached in tar archive. Additionally there is quicktime-animation sample, which appears transparent in kdenlive, as expected. TSCC codec for windows is available here: https://www.techsmith.com/codecs.html
I have tested mlt for supporting transparency in these codecs. I used the following command: melt normal_video.mp4 -track <file> -transition affine where <file> is a png or video file with transparency. Result is the same as for ffmpeg. Here is a table of results: +-----------------+--------+-----+----------+ | container-codec | ffmpeg | mlt | kdenlive | +-----------------+--------+-----+----------+ | png-none | yes | yes | yes | +-----------------+--------+-----+----------+ | qt-animation | yes | yes | yes | +-----------------+--------+-----+----------+ | avi-tscc | no | no | no | +-----------------+--------+-----+----------+ | qt-prores | yes | yes | no | +-----------------+--------+-----+----------+ | qt-cineform | yes | yes | no | +-----------------+--------+-----+----------+ So I can say that the fact that kdenlive is not supporting qt-prores and qt-cineform is definitely a bug. And tscc is probably ffmpeg's unimplemented feature.
Thanks for your detailed report. It is indeed a bug in MLT's qtblend transition that I wrote. It does not correctly detect the alpha channel. I am investigating, but in the meantime, as a workaround you can add a transition to your clips, like cairo blend to force the alpha compositing.
Thanks for reply and for suggestion. I did not know that you are also a developer of mlt. Great respect to you =)!
Now fixed in MLT's git master