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Compressing videos for iPhone 4 - Best quality?

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James Bayliss-Smith
Compressing videos for iPhone 4 - Best quality?
on Aug 23, 2010 at 9:13:20 am

Hi There, I'm a filmmaker and I have a lot of short films that I want to compress for my iPhone. They are all 16:9 and I'm keen to compress them to use the full pixels of the iPhone 4's retina display. i.e 960x540 for 16:9 video. For some reason iTunes will not let me sync the .mov files that I have created.

These are the specs on Apples website:

Video formats supported: H.264 video up to 720p, 30 frames per second, Main Profile level 3.1 with AAC-LC audio up to 160 Kbps, 48kHz, stereo audio in .m4v, .mp4, and .mov file formats; MPEG-4 video, up to 2.5 Mbps, 640 by 480 pixels, 30 frames per second, Simple Profile with AAC-LC audio up to 160 Kbps per channel, 48kHz, stereo audio in .m4v, .mp4, and .mov file formats; Motion JPEG (M-JPEG) up to 35 Mbps, 1280 by 720 pixels, 30 frames per second, audio in ulaw, PCM stereo audio in .avi file format

As far as I can understand they accept .mov file so why can't I sync? I'm new to iPhones so I'm unfamiliar with using iTunes to sync video anyway.

Can anyone make sense of these for me please. I'm looking to get the highest quality possible using compressor, at the moment the only settings that work are the 640 x 320 iPhone pre-set. It seems a pity not to use the full resolution of the screen? Any guidance would be much appreciated.

Thanks

James Bayliss-Smith
http://www.youtube.com/jamesbaylisssmith


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Craig Seeman
Re: Compressing videos for iPhone 4 - Best quality?
on Aug 23, 2010 at 2:15:56 pm

It's not clear what settings you're using. How did you customize the setting? What compression tool did you use?



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James Bayliss-Smith
Re: Compressing videos for iPhone 4 - Best quality?
on Aug 23, 2010 at 4:27:44 pm

Hi Craig, sorry I should have made it clearer. I'm using Apple's Compressor programme. I customised the setting by using the h.264 codec to make a .mov file. I know how to use compressor fairly well I just don't know what format's apple accepts. I can only seem to put files with a .m4v at the end on to my iPhone any others don't seem to sync eben though apple says it accepts these different filetypes. I can create the .m4v using the preset for "Apple devices in compressor but it does not let me manipulate the frame size I can only do 640 x 320.


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Craig Seeman
Re: Compressing videos for iPhone 4 - Best quality?
on Aug 23, 2010 at 4:34:13 pm

mov and even mp4 will work on iPhone. The problem with Compressor is that it auto sets the Profile and Level and that might be the issue. Keep in mind the settings you're attempting will likely only work with iPhone4 as 3GS and below have lower thresholds.

Use this tool to analyze your encode to see if it meets the spec.
http://www.apple.com/downloads/macosx/video/videospec.html



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James Bayliss-Smith
Re: Compressing videos for iPhone 4 - Best quality?
on Aug 24, 2010 at 1:26:05 am

Thanks for the link, I can see that it is a very useful programme although not upadated for the iPhone 4 yet. So I put through my two test videos and everything is the same except for the bit rate

- Bitrate: Max.: Undefined
Average: 15.4 Mbps
Min.: Undefined
- Bitrate: Max.: Undefined
Average: 1 475 Kbps
Min.: Undefined

So I guess 15.4 Mbps is above the "Threshold". Is that what you mean by threshold, the bitrate threshold?

If I cut and paste the specs again from the Apple website and ignore the audio for a moment

Video formats supported [by iPhone 4]:

H.264 video up to 720p, 30 frames per second, Main Profile level 3.1 .m4v, .mp4, and .mov file formats;

MPEG-4 video, up to 2.5 Mbps, 640 by 480 pixels, 30 frames per second, Simple Profile .m4v, .mp4, and .mov file formats;

Motion JPEG (M-JPEG) up to 35 Mbps, 1280 by 720 pixels, 30 frames per second, .avi file format

Does this mean I will achieve better quality with motion Jpeg as I can go up to 35 Mbps?

What is the threshhold for h.264, MPEG 4 is clearly stated as 2.5 Mbs but the H.264 only says up to 720p. What do you think this means?

What is the profile level? What does this mean?

What do you mean when you say Compressor sets the 'level' and the 'profile'? What "level" the bit rate?

Sorry for all the questions I'll do some more reading and some more tests but I'm just trying to get my head around the theory?

Cheers


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Curt Schulz
Re: Compressing videos for iPhone 4 - Best quality?
on Aug 24, 2010 at 8:34:17 pm

Why 15.4 Mbps? This seems like overkill to me. Have you tried multi-pass 2.5 Mbps? I usually encode between 1.5 Mbps and 3.5 Mbps...

Curt Schulz
MBP 2.53 4GB Ram/Mac OS 10.6.4/FCP7.02/Matrox Mini w Max 2.0.0.0150


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Chris Blair
Re: Compressing videos for iPhone 4 - Best quality?
on Aug 25, 2010 at 12:41:48 am

There are even some very high-end encoding apps whose iPhone presets don't work on the iPhone (not even the 3G). The best app on a Mac for making iPhone compliant files that we've found is Handbrake.

It's iPhone presets DO work and they're easy as pie to setup and even customize. But as Craig mentions, you can't mess with the profile or the audio setting as if you get those wrong, it won't be iPhone compliant.

Chris Blair
Magnetic Image, Inc.
Evansville, IN
http://www.videomi.com
Read our blog http://www.videomi.com/blog


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James Bayliss-Smith
Re: Compressing videos for iPhone 4 - Best quality?
on Aug 25, 2010 at 2:12:42 am

Thanks for all your replies and just for the record what are the profile setting for? Excuse my ignorance,


James


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Chris Blair
Re: Compressing videos for iPhone 4 - Best quality?
on Aug 27, 2010 at 11:34:17 pm

The profile determines what the codec is allowed in terms of color space, data rates etc.

They basically are different encoding levels setup to meet a certain set of specifications of intended applications or playback devices. So a lot of the features or capabilities of H.264 are not possible in the majority of codecs used for the web.

For the iPhone and mobile apps, you have to use the lower level profiles since they have tiny and slow processors and the data rate capabilites of celluar data is slow.

There's a more accurate explanation and description of the many profiles here:

http://en.wikipedia.org/wiki/H.264/MPEG-4_AVC#Profiles

Chris Blair
Magnetic Image, Inc.
Evansville, IN
http://www.videomi.com
Read our blog http://www.videomi.com/blog


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