Best file format for still images in QLab
micpool
In an interesting exchange on the FB QLab group, Norimichi Tomita, who is a Resolume user suggested that using png files for stills in QLab was highly inefficient and a much better option was to use HAP, or ProRes 4444, single frame .mov files. He added that Resolume’s manuals stated that for best results all still images should be converted to HAP (or DXV3 which isn’t relevant to QLab).
I thought it would be interesting to see how far this advice was applicable to QLab 5 and devised a quick test using 39 4K images with Alpha transparency in timeline groups with autoload disabled.
(Test Machine was a M1 Max Studio.)
The group containing PNG images took 11 seconds to load, and the images were slightly staggered when they did eventually appear.
Also worth noting was that when the timeline group was started with a start cue, as opposed to a GO when the playhead was at the group, the images loaded 1 at a time over an 11 seconds load time, as opposed to being held and appearing together when they were all loaded which is the behaviour I would expect and what happens with a direct GO.
The timeline groups containing HAP Alpha and ProRes 4444 Alpha single frame .mov files all loaded and displayed all content simultaneously in less than .4 seconds i.e over 20 times faster than the .PNG files. (HAP was faster still, over 30 times faster than the .png files.
So it would appear there are some significant performance advantages using single frame .mov files over the image formats recommended in the QLab Manual, for still images.
However, as usual, that’s not the full story.
In further testing I looked at what happened when the timeline groups were faded over 10 secs.
The .PNG files faded very smoothly
The HAP and ProRes 4444 files didn’t and could only manage a jerky fade with about 5 steps a second.
I also tried playing an 8K video file with darken blend mode on a higher layer than the stills.
With the .PNG files there were some dropped frames on this video when the still images appeared or the fade completed , but normal playback then resumed.
With the HAP and ProRes files this video dropped frames as soon as the still images appeared and continued doing so until the still images stopped after the fade.
I can’t post a screen recording here because of the file size limits but you can view it on FB.
https://www.facebook.com/1333653473/videos/1257647788271634/
