Hello everyone, Not sure whether this is an issue that also exists in the SDL consumers or if I did something wrong on my end, so I decided to post it here as a question.
I'm currently working on a little video editing app in GTK and I made a consumer for it that is utilizing Clutter to display the rendered frames (since I didn't really like the "hack" for the SDL consumer). However I copied most of the SDL (v1) consumer's code with a few exceptions: - I'm creating a separate video thread for rendering the images and then setting the Clutter image to be this image (only in rgb24a format because Clutter doesn’t support YUV as of now) from the main thread. This is because Clutter isn't thread-safe. - I don't really support the "real_time" option on my end because frankly I don't really care for it right now. As I mentioned before, I only want to use this consumer for my GTK app which isn't released yet. On creation, it is set to 0. - Because I don’t know when Clutter is done drawing, I emit an event on the main thread at the end of my video_thread. Here's the C source code for the consumer (without the .yml-, the factory- and all build-system-related files : https://gist.github.com/hannesschulze/e3839a17cfdaabe757abea237f9b4ad2 Now I'm facing the following problem: I have implemented an option to move tracks in my app which removes a track from a tractor (connected to the consumer) and inserts it at another position. This sometimes causes a segfault when the consumer is active and the frame is closed (in l. 616). After a little bit of investigation the issue seems pretty obvious to me (please correct me if I'm wrong; I haven't worked on the framework itself yet): The consumer uses mlt_consumer_rt_frame to get a new frame from the consumer_thread. It then broadcasts the video condition where the video_thread starts to get the image for the frame and tries deleting it. In the meantime, my main UI thread has already moved the track, modifying the tractor and removing/re-adding its transitions for mixing and compositing. I'm using field()->disconnect_service([the_transition]) from MLT++ for removing it from the tractor and Tractor::plant_transition for adding it. The segfault occurs while deleting a service in stack_service (probably the transition?) of another frame which is a property in the first one. After a bit of debugging I found out that this property has been set by the tractor and it just represents the frame for one track (I guess): https://github.com/mltframework/mlt/blob/master/src/framework/mlt_tractor.c#L555 Logically, the transition (or whatever object needed) isn't there anymore. This could just be a problem with my implementation – however, I don't know what might be different from the SDL consumer's implementation so this might affect it too? Is there any way to kind of "lock" the object so that it is synchronized across multiple threads? I haven't found any issues concerning this problem. As of now, I'm unable to stabilly reproduce this issue. If that is necessary, I'll try to get something like this working and also see if it occurs in the SDL consumer. Right now I'm simply wondering if this issue is caused by me or if a bug like this could be possible. System: Pop!_OS 19.10 (based on Ubuntu 19.10) MLT version: 6.16 (from the Ubuntu repos), I haven't seen any changes since then which might fix this but I'll gladly test it on master too Thanks, Hannes Schulze _______________________________________________ Mlt-devel mailing list Mlt-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/mlt-devel
