Audio out of sync with optical out

Question

Audio out of sync with optical out

Hi,

I've connected audio from ATV 2 times to my receiver. My Sony television has an optical out connection so it can act as a passthru for audio to my receiver. However, it's always stereo, I can't get surround from it. Apple says it sends the same audio over HDMI and optical out. So I connected ATV directly to my receiver with the optical output. Result: I do have surround now. So I guess my Sony is at fault for not passing along surround.

This is my setup:

1) ATV -> HDMI -> Sony LCD -> optical out -> receiver
2) ATV -> optical out -> receiver

My problem:
Setup 1) gives me no surround but audio and video are synced perfectly.
Setup 2) does give me surround, but audio and video are OUT of sync.

My video is generated by Handbrake 0.9.3 and contains both AAC stereo and AC3 surround passthru.

It's strange, because if you have this audio delay problem you would think it's caused by the television because that's an extra device sitting between source and receiver.

Any ideas what is causing this problem? Is Handbrake not able to add AC3 correctly or is ATV playing sound in sync over HDMI but not in sync over optical out?

Thanks,
Jef

MacBook Pro 2,4Ghz, Mac OS X (10.5.6)

Posted on Jan 3, 2009 7:56 AM

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Answer 1

Sep 3, 2018 1:06 PM in response to Winston Churchill

It's the other way around: via television gives no syncing problems. It's the optical out connection directly from ATV to receiver that gives me the delay problems.

Indeed I can also add a delay with my receiver, but that will only worsen the problem since the audio signal is already delayed.

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Answer 2

Sep 3, 2018 1:06 PM in response to Winston Churchill

Thanks for your response.

Are you sure the audio isn't ahead of the video, if not:

a) your receiver already has a delay set over that port.

Yes, sure about it, just double checked it.

b) there is something wrong with the file itself.

This is of course a bit the unknown factor since I used Handbrake. I'm experimenting with different settings. Unfortunately you can't convert a file while preserving surround by using QT Pro. It would be a nice comparison if you could use default Apple applications.

c) your receiver is slow at processing the ac3 audio (stereo may not present the same problem)

Could be, but never had any syncing problems during 5 years.

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Answer 3

Jan 3, 2009 8:20 AM in response to Community User

Your tv and receiver will both be receiving their signals in sync, but one of the devices will be processing that signal faster than the other. It's most likely that the tv is the slower of the two and the receiver has an insignificant processing delay. Your tv was likely holding up the audio output to keep it in sync with the video.

Your receiver most likely has a delay setting to compensate for what you are experiencing, you will need to refer to its manual to learn how to change these settings.

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Answer 4

Jan 3, 2009 9:11 AM in response to Community User

Jef Van der Voort wrote:
It's the other way around: via television gives no syncing problems. It's the optical out connection directly from ATV to receiver that gives me the delay problems.

Yes I understand that

Indeed I can also add a delay with my receiver, but that will only worsen the problem since the audio signal is already delayed.

Are you sure the audio isn't ahead of the video, if not:

a) your receiver already has a delay set over that port.
b) there is something wrong with the file itself.
c) your receiver is slow at processing the ac3 audio (stereo may not present the same problem)

FWIW, my audio and video are in sync, my tv is connected by HDMI to the tv and my receiver is connected by optical to the tv.

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Answer 5

pvonk

Level 6

13,857 points

Jan 3, 2009 6:15 PM in response to Winston Churchill

"FWIW, my audio and video are in sync, my tv is connected by HDMI to the tv and my receiver is connected by optical to the tv."

Winston - I have the same setup as you describe. I frequently find the audio and video out of sync by a smidgen when playing Handbrake converted movies/TV shows. I don't seem to have the problem with my DVD player (has separate HDMI to TV and composite to receiver), nor with iTunes movies. Samsung LCD and Denon receiver.

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Answer 6

Jan 3, 2009 6:40 PM in response to pvonk

All my videos with ac3 tracks are itunes movies or home videos too.

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Answer 7

Mar 5, 2009 6:36 AM in response to Community User

You are not alone with this problem - am experiencing the identical problem with many of my videos encoded with AC3 soundtracks. The audio is either completely out of sync (always ahead of the video), or it fades in and out of sync as the video plays. Curiously, this ONLY seems to effect AppleTVs sending audio through the optical output, as my other AppleTV is connected via HDMI for both audio and video is always completely in sync.

I believe this is an AppleTV firmware bug and have submitted a report through Apple's Developer connection. I would encourage you do the same in order to bring more attention to this problem.

You can visit it using this link: https://bugreport.apple.com

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Answer 8

Mar 5, 2009 7:25 AM in response to Community User

Thinking about this a bit more, I think I could have an idea as to what the problem is - the AppleTV firmware. I believe that there is a timing difference between HDMI and the optical audio output. Let me explain...

My AppleTV is hooked up using HDMI for video only (direct to my TV) and the optical is hooked up directly to my audio receiver. Since there is no setting in the AppleTV menu to choose the output for the audio, I have to assume that it's sending audio through BOTH the optical output and the HDMI output simultaneously. If the timing for the audio signal is slightly different, then that could cause the audio to be out of sync. Since the HDMI signal carries both audio and video, it makes sense that it would remain tightly in sync. But since the optical is separated it could, theoretically, not be synced with the video.

As I said, both of these AppleTV units have been hooked up the identical way that they are now and have never exhibited this problem until the 2.3/2.3.1 firmware updates.

I also noticed that unplugging the unit from power for 10 minutes, plugging it back in and testing the identical file that minutes earlier was out of sync, that the video and audio were much closer to being in sync. Does this make any sense?

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Answer 9

Mar 15, 2009 5:27 PM in response to John Finley

just jumping in new to the thread. i get this problem also. all my efforts to sort it out seem to point at there being a problem with the sync on the optical out on the apple tv.

i use handbrake to encode (apple universal preset). files play fine in itunes and are in sync via the hdmi audio on the tv. the optical out is often out with 5.1dd soundtracks.

sometimes pausing the apple tv then starting again corrects it a bit sometimes it makes it worse.

ive noticed handbrake encodes 5.1dd sources as aac for front channels and ac3 passthrough for the rear. i read somewhere it had to do this to get apple tv to play the files. could this mismatch be the problem?

does apple tv play files that are encoded with ac3 passthrough on all channels?

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