iPad Quicktime decoder limited to 3 ref frames

[UltraTV]

Just wanted to give a heads up to anybody encoding for iPad. Encoding with --profile main --level 3.1 --tune film and basically nothing else set results in broken playback on the iPad. The iPad will open the file, but it goes bonkers every few frames with a bunch of broken macroblocks or whatever.

In any event, if you want to encode a playable file use --ref 3 or lower with the above settings.

Anybody else notice this? I looked around but couldn't find a hard reference frame limit in the Main profile. Is this Quicktime dousching out or is this a relatively normal limit for devices?

If it's a standard thing for devices it might be good to change --profile main to default to --ref 3. I'm not sure there's that large of a need for the extra reference frame if it causes more headaches for users creating videos for devices.

[nurbs]

Maximum number of reference frames depends on the level and resolution of the video. See the H.264 article on Wikipedia (english) for examples.
BTW did you try a high profile encode. Since the iPhone 3GS can do high profile (although Apple says it can't IIRC) the iPad should handle that too.

[SeeMoreDigital]

Hmmm...

I've been generating QT7 and iPhone compliant encodes with "four" and even "five" reference frames for a while now. It would be most odd if the iPad could not support these too!

Can you try some of the following and report back please: -

http://www.stuartgraham.tv/new/


Cheers

[UltraTV]

plays fine... weird, let me dig into this a little more. i'll try to get high profile playing back as well.

[Blue_MiSfit]

This is more than likely Apple douching out the H.264 decoder :p

IIRC, the iPhone 3GS would play 1080p at reasonable bitrates, but you had to transfer the file to it outside iTunes (via SCP or FTP or something). I bet the iPad will be the same story. Both likely use a reasonably powerful ASIC for H.264 decoding.

~MiSfit

[UltraTV]

Gotta love Quicktime... :rolleyes:

Anywho, I'm unable to reproduce this with other video clips. I'll try again on Monday with the original clip and work back from there...

Sorry to raise the alarm on this. Looks like it's a pretty limited issue at worst.

[Blue_MiSfit]

quicktime == ragequit.

[Ritsuka]

You know, there is no QuickTime on the iPad. :P

[me7]

From my experience iPod/iPhone support up to 6 reference frames at PAL resolution (720x576). Try try same on your iPad.

[lych_necross]

You know, there is no QuickTime on the iPad. :P
I thought that was flash? :D

[AlekseiV]

I've been generating QT7 and iPhone compliant encodes with "four" and even "five" reference frames for a while now.Why the scare quotes?