[Dorian Gray]

Among the changes listed by Apple for the QuickTime 7.1 update is an improvement in "H.264 performance". Does this mean an increase in image quality or a decrease in decode/encode time? I did a test to find out.

I took a 90-second video clip and exported it to Motion JPEG B at 100% quality (lossless with 4:2:0 chroma subsampling), discarding the audio track. The video was 640 x 272 pixels in size with a frame rate of 23.98 FPS. I then played this Motion JPEG B video in QuickTime Player, using Activity Monitor's Inspect feature to determine the total CPU time consumed by playing the video once. The result was 25 seconds on my iBook G4 1.2 GHz.

I then rebooted my Mac and exported the Motion JPEG B MOV to a single-pass H.264 MOV at 500 kbps with a keyframe interval of 150 (i.e. typical settings for highly compressed H.264). This took a total time of 5 minutes and 6 seconds.

Then I updated to QuickTime 7.1, did the standard post-update maintenance, rebooted again for good measure, and did the same export with the new version of QuickTime. Total time was 4 minutes and 45 seconds.

Subtracting 25 seconds from these times (to eliminate the Motion JPEG B decode time) gives us times of 4 minutes and 41 seconds for QT 7.0.4 and 4 minutes and 20 seconds for QT 7.1.0. This represents a time saving of 7.5%. The quality of the two videos is subjectively identical, but there are many differences at the pixel level. As it is inconceivable that the quality would have deteriorated with an update, it is possible that the quality could be subjectively better under certain conditions.

Nice one, Apple! It's great to see that resources are still being spent on optimising the PPC code for G4 (and presumably G5) users. If anyone with a G5 who hasn't updated QuickTime yet is anal enough to care about this, please do a similar test and post your results here!

I noticed another welcome improvement: when you drag a QuickTime Player window to the top of the screen with some of video extending past the left-hand-side (or RHS) of the screen, and then hit Command-1/2/0, the window is made to fit exactly into the top-left corner (or top-right corner), rather than with a gap as before. Command-3 no longer suffers from the bug of getting it "almost there" after one action, then making a slight correction on the second attempt (I used to hold Command and hit 3 twice to correct for this). Command-3 also now centralises the movie vertically on the screen.

Good job all around.

PS. I hope this isn't too philosophical torifile!

[gjas15]

I tryed out these "performance improvements" on my 1.67 powerbook and was very pleased. I can now playback 720p h.264 smoothly. Before, it would be fine until I hit a high motion scene and playback would stutter a bit. True, I do have to close everything i possibly can and have only quicktime running, but now it can be done!

Does anyone know if the Quicktime H.264 encoder now supports high profile and any of the other really advanced features of H.264?

[chucker]

Originally Posted by gjas15 Does anyone know if the Quicktime H.264 encoder now supports high profile and any of the other really advanced features of H.264?

I couldn't find such a setting, no. I'm not an expert at this, however.

[nato64]

Wow... that's all I can think of. That's an intense test! So many numbers it sounds like official documentation.