Open Radar

 
07-Mar-2012 08:58 PM Jon Stacey:
Summary:
Video played in iTunes and Quicktime will stutter for a about 1 second when an OSD appears, such as when the volume is changed. This occurs both in windowed and fullscreen modes. The problem seems to be rooted in CoreVideo, or an interaction between CoreVideo and when the OSDs activate, because the problem is not present when playing the same files through another video player such as VLC. It is also not specific to the video file themselves because the issue is present on both iTunes Store purchased videos and homemade videos when played through iTunes or Quicktime.

Steps to Reproduce:
Prepare a test video that captures something that moves smoothly and predictably so that it is easy to visually detect the stutter. Load the video into iTunes and play it from there in either fullscreen or windowed mode. Perform an action that causes an OS X OSD to display. For example, change the volume.

Now, play the video with Quicktime. The issue will be less prominent and noticeable, but still present.

Finally, play the video with another video player such as VLC that does not use CoreVideo. The problem is no longer present.

Expected Results:
I expect the video to continue playing without stutter when I activate some OS X builtin OSD such as changing the volume. That is an action that is quite frequent during video playback.

Actual Results:
The video appears to slightly stutters for about 1 second right after the apex of the OSD. That is, the OSD appears without stuttering. The stuttering occurs during the very beginning part of the OSD fadeout process, but then appears to stop stuttering just before the OSD completely goes away. The OSD fadeout does not stutter which indicates its a specific problem with iTunes/Quicktime and/or one of the underlying libraries that they are using.

Regression:
This problem also existed in iTunes 10.5.

Notes:
iTunes was the product that I first noticed this bug on. However, since it's also present in Quicktime, and thus pointing to a problem in CoreVideo, it could also be filed under a different product category.

I will attempt to attach a small video sample of each application demonstrating the problem. I used Quicktime Player to capture the screens and it introduced some very slight stuttering throughout, but the stuttering that I'm reporting in this bug report is still noticeable just as the volume OSD begins to fade away. The VLC playback is butter smooth on the actual system.

07-Mar-2012 08:58 PM Jon Stacey:
'iTunes Demo.mov' and 'iMac.spx' were successfully uploaded

07-Mar-2012 08:59 PM Jon Stacey:
'Quicktime Player Demo.mov' was successfully uploaded

07-Mar-2012 09:00 PM Jon Stacey:
'VLC Demo.mov' was successfully uploaded