[mythtv-users] OT: XBMC on Apple TV2 and iPad

Raymond Wagner raymond at wagnerrp.com
Sat Jan 22 03:52:12 UTC 2011

On 1/21/2011 17:45, belcampo wrote:
> Raymond Wagner wrote:
>> On 1/21/2011 15:41, Matt Emmott wrote:
>>> It changes everything in that, you now have a small portable device 
>>> with a great front end to all your media.
>> This changes nothing, yet.  The published performance specs for the 
>> A4 chip are hardware accelerated h.264 up to Main Level 3.1.  No 
>> MPEG2, so that cuts out the bulk of digital TV.  No h.264 Level 4.1, 
>> so that cuts out the rest of digital TV and output from an HDPVR.  
>> Lack of that, and VC1, means no Bluray playback either.  From the 
>> published information on the chip, it's still garbage requiring any 
>> content be transcoded down to low quality specifically for that device.
> Not LowQuality, but the same quality at a 'little higher' bitrate.
> Main3.1 is as good as High3.1 with the same crf or qp settings.

High gets you some additional transforms, and slightly higher bitrate, 
but that's not what I'm talking about.  I'm talking about the ATV2 only 
officially supporting Level 3.1, but the rest of the hardware decoding 
world doing 4.1.

> Bitrate is NOT = QUALITY
> Better encoder produces same quality in less bits.
> I've done several BluRay encodings with qp=24, between 16 - 26, most 
> people perceive this setting 'almost as good' as the original. 
> Resulting bitrates drop from 32-38Mb/s to 3-7Mb/s on average.

qp=24 is a pretty high setting.  Perceivable lossless for x264 is 
generally considered to be somewhere around 18-20.  Some parts of some 
1080p content may look good at 7Mbps.  If you have a lot of film grain, 
it's going to get averaged out into a blurry mess.  If you have smooth 
gradients, they will get replaced by a single color field.  If you have 
high motion, you're going to end up with all sorts of nasty blocking.  
It's nothing like 'almost as good', but then of course the average user 
is happy with theater cams, and runs their nice 24" monitor at 1280x800 
because 'everything is too small on screen'.

However this whole argument is irrelevant.  The key point of my post is 
that the ATV2, as specified by the Apple website, will not handle any HD 
content recorded by MythTV in its original form.  You will need to spend 
vast amounts of time transcoding at a fraction of real time, to get your 
content down to a form playable on the device.  Until the XBMC devs get 
some real performance information about the real capabilities beyond of 
the specs published by Apple, it is too early to plan anything.  They're 
not going to do so until the code evolves beyond an unstable, 
developmental branch (that's the answer they gave when I asked).

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