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

Christopher Kerr mythtv at theseekerr.com
Sat Jan 22 10:17:21 UTC 2011

On Sat, Jan 22, 2011 at 8:14 PM, belcampo <belcampo at zonnet.nl> wrote:
> Raymond Wagner wrote:
>> 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.
> I know all these arguments, do you have any material to proof these ? Side
> by side of course.
>> It's nothing like 'almost as good',
> I've done a lot of actual testing, believe my eyes more then the words of
> others.

And that's the wonderful thing about perceptual lossless encoding -
it's remarkably subjective. Personally, I find that qp=24 H.264
(encoded with x.264 using Handbrake, FWIW) is unwatchable on anything
beyond talking heads (I find qp=21 acceptable for most TV material
(not movies), and qp=19 fine for movies.) Fast motion gets blocky.
Dark backgrounds get blocky. Skies (and other gradients) often develop
one really obvious band in the middle somewhere.

But it is, after all, designed to be hard to notice, so if you don't
notice it, that's all the better for you.

- Chris

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