Apple TV Audio Hardware Too Weak?

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Confused Amused
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Joined: Wed Mar 28, 2007 6:27 pm

Apple TV Audio Hardware Too Weak?

Post by Confused Amused »

Am I the only one having problems playing high quality videos with 6.0 AAC on the aTV?

Has anyone used settings in this neighborhood:

MP4 h264
Anamorphic
6.0 AAC
74% CBR or 5000 kbps VBR w/ 2 Pass

My videos play great on my iMac, but I definitely see stuttering and the audio off-sync on my aTV. If I drop down to 5.1 the videos seem fine. Is the hardware not capable of decoding the 6.0 audio fast enough?

tg3
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Post by tg3 »

Hacked or stock aTV? File is synched or streamed? Diff in file sizes?

jbrjake
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Post by jbrjake »

What do you mean by dropping down to 5.1 audio from 6-channel?

Confused Amused
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Joined: Wed Mar 28, 2007 6:27 pm

Post by Confused Amused »

Stock aTV. Haven't modded anything.

I meant I see a difference on the aTV (but not my Mac) if I encode using 5.1 AAC or 6.0 AAC. 6.0 causes the audio to be off sync and the video playback to be choppy while it seems fine encoded at 5.1

incubowski
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What?

Post by incubowski »

Wait, what? There is 5.1 and 6.0 aac, I don't get it.

jbrjake
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Re: What?

Post by jbrjake »

incubowski wrote:I don't get it.
Me neither.

Confused Amused
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Joined: Wed Mar 28, 2007 6:27 pm

Post by Confused Amused »

Hmm, ok, guess I'm not explaining this well.

In the audio settings, under Language 1 I select English (AC3) (5.1). I encode a movie with that and it looks fine on aTV.

If I check the box next to that "Extract 5.1 Dolby Digital to 6-channel AAC", and encode a movie, the video suffers on aTV like I mentioned above. Plays fine on the Mac though.

jbrjake
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Post by jbrjake »

Confused Amused wrote:Hmm, ok, guess I'm not explaining this well.
It's not your explanation, it's your terminology. From CBR to VBR to 5.1, you're misusing the words.

What you seem to be trying to report is that the AppleTV is having trouble with 5.1 AAC audio and not stereo AAC audio.

And you still haven't answered about whether you're streaming or syncing.

Confused Amused
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Joined: Wed Mar 28, 2007 6:27 pm

Post by Confused Amused »

Whatever works. Change "5.1" in my original post to "stereo" and I think it's straightforward. I tried both with a CBR of 74% and then I tried some tests with a a 5000 VBR with 2-pass encoding.

But yeah, I've read all the posts about how the aTV can't actually output the 5.1 audio but I was trying to plan for a future update or hack that would allow this by encoding my videos with the 5.1.

From what I've read the aTV will mix down the 5.1 to a stereo signal, but my tests were showing that while it might be able to do it,the aTV doesn't do a good job of it. Seems like it's having trouble keeping up.

And this files are synced, not streamed.

cbud
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Post by cbud »

Try to lower the video bitrate until you get smooth playback. You might have to live with a lower bitrate if you want 5.1 AAC. You have not told us what your audio bitrate is, maybe you can lower that as well.

Confused Amused
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Post by Confused Amused »

That's something I haven't tried yet, but in the end I think I'd prefer a better video bitrate and settle for stereo sound.

I've experimented with audio bitrates of 192 - 320 kbps with them all being the same result. I guess I can drop it below 160 which is what the aTV is officially rated for.

Confused Amused
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Post by Confused Amused »

Looks like it was the video bitrate causing this. A bitrate of 2300 played back smoothly, but 3700 gave it the same jerkiness I was describing earlier. At both those video rates I used 192 kbps audio extracted to 6.0 AAC surround sound. 2300 kbps video bitrate was fine, but 3700 kbps had issues so it looks like the video GPU is what's causing this.

I can't possibly be the only one encoding videos at this bitrate though for archival purposes, am I?This is a real bummer that the aTV isn't going to work so well for me. Oh well, maybe I'll be selling this and waiting for the refresh to the Mac Minis and hope Leopard comes with this new GUI.

Confused Amused
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Joined: Wed Mar 28, 2007 6:27 pm

Post by Confused Amused »

Ugh, I'm a little more concerned about this now. I've since returned my Apple TV, but yesterday I loaded up an installer on my iMac that replaces Front Row with the new Apple TV program. Fired it up, it works great. I can browse my music, movies, TV shows, etc on my iMac, but using the Apple TV interface.

I've been encoding my videos with h.264 CRF, quality set to 72%. Videos play great in Front Row 1.0/Quicktime. No stuttering or jerkiness. The exact same videos have the same problems I described earlier where the audio and video seems slightly off and there's some stuttering during high-action scenes. Not enough that it's terribly obvious, but certainly enough to be annoying. It almost seems like Apple TV's software is the problem rather than the hardware. I'm certainly over the official bitrate specs with these movies so I'm not terribly surprised it doesn't work correctly, but I sure hope Leopard's Front Row doesn't have this limitation. I love the new Apple TV interface, but had to resort back to Front Row 1.0 for the time being.

loyalty_anchored
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Post by loyalty_anchored »

Confused Amused wrote:That's something I haven't tried yet, but in the end I think I'd prefer a better video bitrate and settle for stereo sound.

I've experimented with audio bitrates of 192 - 320 kbps with them all being the same result. I guess I can drop it below 160 which is what the aTV is officially rated for.
there is a very good reason for this, HB can only encode each AAC channel to a maximum of 80 kbps. so for stereo, anything selected over 160 will not be encoded at a higher bitrate. for 5.1 i would recomend 64 kbps per channel which would give you a total bitrate of 384.

Confused Amused
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Post by Confused Amused »

Yeah, I read that later too, but thanks.

Ultimately, my encodes all ended up being anamorphic h.264 at 72% - CRF with 224 kbps Dolby Pro Logic II mixdown for the audio. Suits me just fine.

loyalty_anchored
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Post by loyalty_anchored »

Confused Amused wrote:Thanks, but those points above aren't any settings I ended up using.

Ultimately, my encodes all ended up being anamorphic h.264 at 72% - CRF with 224 kbps Dolby Pro Logic II mixdown for the audio.
the thing i am trying to tell you is the following, it does not matter how high of a bitrate you specify in HB for a stereo 2 channel audio, it will not allocate more then 80kbps per channel (give or take a few kbps depending on the SampleRate). so the fact that you encoded at 224 for stereo, means you really have a resulting file that is 160. this is a little off topic for this thread so i am not going to go back and forth with it, i just wanted to give you a heads up on something i learned the hard way.

goodluck!

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