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Audio quality on Apple TV G2.

2256 Views 18 Replies Latest reply: Jun 11, 2011 9:44 PM by Jon Walker RSS
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Guilherme de Assis Brasil Calculating status...
Currently Being Moderated
May 15, 2011 8:34 AM

I bought my Apple TV (G2) with the goal to no longer put my CDs and DVDs in a CD/DVD player and so have my audio library, concerts and movies cataloged into iTunes.

I've converted all my CDs (which are originally stereo) to MP3 but now I need convert my DVDs. The big question is regarding the audio quality, because most
of my DVDs has original sound in DTS. How do I convert the DVDs to make sure the Apple TV will play the 6 channel (5.1) with the same quality as the original DVD?

AppleTV 2
  • Rudegar Level 6 Level 6 (18,480 points)
    Currently Being Moderated
    May 15, 2011 9:49 AM (in response to Guilherme de Assis Brasil)

    try taking a look at the program called handbrake (only for non encrypted dvd's of cause)

  • Jon Walker Level 6 Level 6 (17,520 points)
    Currently Being Moderated
    May 15, 2011 2:46 PM (in response to Guilherme de Assis Brasil)


    I'm using HandBrake, but I have doubts to which codec and
    format should I use to convert the audio to get 5.1 output.

    Use the AC3 "Passthrough" option for the selected 5.1 audio track under the "Audio" tab. (This should be the default for the TV pre-set option.)

     

    small_white_chi.gif

    2.66GHz 17, Mac OS X (10.6.6), 60GB 5G iPod, 4GB iPhone, Nikon D-70, Nikon CoolPix 990, Sony HD
  • Jon Walker Level 6 Level 6 (17,520 points)
    Currently Being Moderated
    May 15, 2011 6:12 PM (in response to Guilherme de Assis Brasil)

    John, I did the DVD extraction using AC3 "Passthrouh" and as the file information shows, the 6 channels were maintained as the original source.

     

    infos.jpg

     

    Since you did not include stats on the audio, I do not know what data rates you are dealing with here. Excessive AC3 data rates like 640 Kbps (BD AC3), AFAIK, are still not supported by the TV2 device and DTS can be as high as 1509.75 Kbps if I remember correctly. In any event, when I suggested the AC3 "Passthrough" I was referring to true AC3 content and not DTS. Owing to previous problems with DTS, I normally extract just the AC3 when both DTS and AC3 are available on a disc. Have queued a DTS file for conversion sometime later tonight. (Currently updating my Banacek files from AAC only to AAC with secondary AC3 audio track.) As this will probably take all night to finish, I will post back after trying to duplicate your work flow in the latest update. (I.e., have not used this work flow for some time and need to see if anything has changed since I last used it.)

     

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    P.S.

     

    Two quick questions:

     

    1) Is there any particular reason you are pushing the total data rate so high, and

     

    2) is your audio track active or passive?

    2.66GHz 17, Mac OS X (10.6.6), 60GB 5G iPod, 4GB iPhone, Nikon D-70, Nikon CoolPix 990, Sony HD
  • Jon Walker Level 6 Level 6 (17,520 points)
    Currently Being Moderated
    May 15, 2011 8:44 PM (in response to Jon Walker)

    FOLLOW-UP:

     

    Managed to pause my work flow long enough to run a quick DTS conversion test. Used the following settings:

     

    TRACK:             DTS 5.1 ch

    CODEC:            AC3

    MIXDOWN:       6-channel discrete

    Samplerate:     Auto

    Bitrate (kbps): 448

     

    I suspect you are using the default 640 Kbps audio data rate in your runs which is likely the source of your TV playback problem. Also, you did not indicate what support your are using for iTunes playback so I cannot comment on possible problems in this area. Just remember that AC3 is not natively supported by QT, so whatever problem you are having is likely tied to the software/hardware you are specifically using on your computer. I avoid this problem by using AAC audio as my primary (active) audio track and AC3 as my secondary (passive) audio track. This makes the same file compatible with iPhone 4, iPad, iPad2, and all of my TV2 devices. Computer and mobile devices automatically use the AAC track and the TV2 devices automatically use the AC3 track.

     

    In any case, using the above settings, my test file played in iTunes on the computer using AAC stereo audio, Air Played wirelessly on the nearest TV2 device using AC3 5.1 audio, and played via ethernet connection as selected from the same TV2 device again with AC3 5.1 audio. I.e., I see no real problem with this work flow if AC3 audio data rate is reduced to a more reasonable/normal/expected level.

     

    Hope this helps...

     

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    2.66GHz 17, Mac OS X (10.6.6), 60GB 5G iPod, 4GB iPhone, Nikon D-70, Nikon CoolPix 990, Sony HD
  • nightstorm Level 1 Level 1 (30 points)
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    May 16, 2011 6:30 AM (in response to Jon Walker)

    The AppleTV v2 has no problems passing through AC3 at 640kbps.  If you use one of the nightly Handbrake builds, you should be able to convert DTS to AC3 via the options on the audio tab.  I typically recommend using 640kbps AC3 if you are converting from a higher bitrate source.  I would also recommend you follow the same track format as the AppleTV v2 preset in Handbrake (1 AAC track for compatibility, 1 AC3 track for surround).

  • Jon Walker Level 6 Level 6 (17,520 points)
    Currently Being Moderated
    May 16, 2011 7:52 AM (in response to nightstorm)

    The AppleTV v2 has no problems passing through AC3 at 640kbps.  If you use one of the nightly Handbrake builds, you should be able to convert DTS to AC3 via the options on the audio tab.

    Thanks for your input. My original test at 640 Kbps was made last year using v0.9.3 (or v0.9.2) if I remember correctly. Went back and re-compressed latest test file at 640 Kbps this AM and it too played correctly. Will try re-compressing the original file test made last year to see if it will also play correctly now or if that specific audio conversion actually overruns the target 640 Kbps limit. Would be interesting to learn if current success is due to changes in HandBrake or changes made to the TV2 firmware since original tests or is simply related audio target data rate overruns. Anyone else have input regarding this issue?

     

    I would also recommend you follow the same track format as the AppleTV v2 preset in Handbrake (1 AAC track for compatibility, 1 AC3 track for surround).

    Would be nice if the OP would re-compress his problem file with both AAC/AC3 audio tracks and see if that solved his original on-again/off-again playback issue, as well as, indicate the actual AC3 audio data rates resulting from his conversions. (For that matter, it would be nice to know if excessive video data rates play a part here by bogging down iTunes ability to stream/attempt to stream data to the TV2 device.)

     

    Again, thanks for your comments as I am still trying to create custom pre-sets for DTS and HQ AC3 work flows that work 100% of the time and/or provide an audible difference to my current state of continuously failing aural acuity.

     

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    2.66GHz 17, Mac OS X (10.6.6), 60GB 5G iPod, 4GB iPhone, Nikon D-70, Nikon CoolPix 990, Sony HD
  • Jon Walker Level 6 Level 6 (17,520 points)
    Currently Being Moderated
    May 16, 2011 9:30 PM (in response to Guilherme de Assis Brasil)

    HandBrake.jpg

    What's the problem with the configuration I presented in the figure above?

    Why my iTunes has difficulties to play the file created from this setup and my AppleTV2 even can't start to play it?

    Normally, the best approach is to initially use the "AppleTV 2" pre-set provided. Then, if necessary, modify those settings to meet your specific needs. For instance, the "AppleTV 2" preset will generate two audio tracks as depicted here...

    Screen shot 2011-05-16 at 10.49.00 PM.png

    As seen here, the first audio track, an "active" AAC audio track, is automatically used by QT media players (like the iTunes player). This ensures that all users can hear the audio when the movie is played back in iTunes. (As previously stated, QT does not natively support AC3 audio and that is why you only hear "noise" when currently playing your movie in iTunes.) The second track, the AC3 is normally used automatically by your TV2 device depending on your TV2 audio preference settings.

     

    audio.jpg

    As seen here and was previously pointed out, your total average data rate is excessively high. Since your total average data rate is listed as 13.967 Mbps and your AC3 target audio data rate is 640 Kbps, this implies your video data rate is on the order of 13.327 Mbps for an standard definition file. This is 30 to 50% higher than would normally be used for a 720p high definition or 200 to 300% what is normally used for a standard definition encoding. Since the theoretical maximum video data rate supported by the TV2 device is only 14.0 Mbps, it is very likely that this is what is "over taxing" your iTunes playback and causing "difficulties." It also means your TV2 device would have to cache significantly larger amounts of data to its memory before it could attempt to begin playback. Once again, using the built-in "AppleTV 2" pre-set settings would lower your video data rate to a much more reasonable figure which, in turn, will likely allow the file to play without difficulties in iTunes and also play correctly on your TV2 device.

     

    Jon and nightstorm, actually I'm not an expert of audio and video converting processes, and my biggest concern is to be able to play my DVDs contents from AppleTV2 with the same quality of video and audio (mainly) when I play directly from the original DVD.

    As a "rule of thumb," an H.264 (MPEG-4/AVC) video data rate roughly equal to half the video data rate of the MPEG-2 source file should produce visual quality roughly equal to the source file. Since most average DVDs use MPEG-2 video data rates in the 5.0 to 8.5 Mbps range, you should achieve good results with H.264 data rates in the 2.50 to 4.25 Mbps range. The "AppleTV 2" quality pre-set value is 20 and I rarely use anything greater than a value of 17. (NOTE: the lower the number the higher the quality. I.e., increasing the setting any higher produces virtually no increase in quality while continuing to increase the file size and eventually probably causing the problems you are now experiencing.

     

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    2.66GHz 17" MBP 2.0GHz 3GB G5/533MHz 384MB G4 DeskTop/400MHz 384MB G4 Ti PB, Mac OS X (10.6.6), 60GB 5G iPod, 4GB iPhone, Nikon D-70, Nikon CoolPix 990, Sony HD
  • Jon Walker Level 6 Level 6 (17,520 points)
    Currently Being Moderated
    May 18, 2011 12:00 PM (in response to Guilherme de Assis Brasil)

    For audio, I did two tests:

    FIRST TEST:

    teste1.jpg

    teste1-infos.jpg

    In this first test the file was played perfectly in iTunes (MacBook) and AppleTV2. Theoretically, I've got a 5.1 audio in AppleTV2.

    SECOND TEST:

    teste2.jpg

    teste2-infos.jpg

    In this second test, iTunes perfectly played the file but AppleTV2 had an error and didn't played it.

    You are still creating single track audio files. What nightstorm and I were suggesting is that you use the default audio pre-set also. This should ensure compatibility across both systems and devices. Some users have complained that movies containing only the AC3 audio track won't play on their TV devices. Others state that they do play. On my system the ones I've tested with only AC3 audio do play, but since this represents only a few random tests, I cannot say that all such files made this way will play. On the other hand, all of the files I've made with AAC only and AAC + AC3 audio tracks have played correctly (other than my initial 640 Kbps AC3 passthrough test made a year or so ago).

    Screen shot 2011-05-16.jpg

    Once again, as you can see, the default Audio preset creates two audio tracks. The first, a stereo AAC track is encoded as Pro Logic II audio using a target data rate of 160 Kbps with a 48.0 KHz sampling rate. This track is the "default" audio used by systems and/or devices not capable of playing AC3 DD5.1 audio. In addition, if connected to a "active" PL II decoder, it will play surround sound. While not true "discrete" surround audio, it is generally audibly better than "passive" PL decoding. As to the AC3 DD5.1 track, it is normally played by "default" when played through an TV device connected to a AC3 DD5.1 decoder equipped TV, receiver, or amplifier and the user has not turned off the passthrough capability.

     

    Picture 12.jpg

    Picture 13.jpg

    Here are the statistics for two test clip snippets taken from the same file encoded using my TV preset. As you can see, the audio and video data rates can vary by quite a degree during encoding. This will give you some idea as to how movie content can "drive" the encoder during the compression process. In the first snippet, there is a rapid close-up pan (very difficult to encode) and frequent loud noises in the background that help to drive up the data rates. The other snippet is what I tend to think of as a typical average indoor scene. In any event, I have uploaded both test files so you can download and test then on your system and/or TV device if you wish. I would be interested to know if they play correctly in both iTunes and on your TV2.

    Test

    Test2

     

    Now I have the following questions:

    - Will I get the best (same as the original AC3 5.1 source) audio quality with AAC?

    - Why my AppleTV2 couldn't play the content with AC3?

    Apple recommended preset is 64 Kbps data rate at 44.1 KHz sampling rate per channel. (I.e., 128 Kbps at 44.1 KHz for stereo.) When listening to things like piano overtones or rain falling on an empty street, I can hear a difference between these settings and stereo 160 Kbps at 48.0 KHz. So I admit I do use the latter for may AAC track. However, as I am on the "high side of 65" and my hearing is not as good as it could be, I really do not hear any differences above these settings. If you want you can try using stereo 320 Kbps at 48.0 KHz and see if you can hear any differences in the quality. Frankly, your target data rate of 448 Kbps seemed higher than necessary for stereo.

     

    As to a comparison of AAC with AC3, a stereo 160 Kbps/48.0 KHz audio track is supposed to equal a stereo AC3 track at 192 Kbps/48.0 KHz which is the standard for DVD. As to AC3 DD5.1 the standard for a DVD is 448 Kbps at 48.0 KHz. As you can see if the data rate were divided equally between all 6 channels, the the allocation would only be about 75 Kbps per channel. Luckily, sounds allocated to each of the 6 channels rarely, if ever, require to push the full amount of data through all channels simultaneously. It might be more appropriate to say that each AAC channel has a higher sustained quality potential than each standard AC3 track, but that the increased number of AC3 channels provides a potential for more natural, directional sounds.

     

    As to your not being able to play your AC3 only files, there simply is not enough information to evaluate at the moment. For instance, your system may be one that wants/requires/expects an AAC track be included in the file. Or, as previously mentioned, the audio data rate for your output files may exceed the limits allowed for streaming to the TV2 device. For that matter, while all of my tests were made using the "Auto" setting to output audio at 48.0 KHz, your screen shots of target settings do not confirm that your file output is, in fact, using a 48.0 KHz sampling rate. (I.e., some TVs/receivers may not accept other sampling rates which may be why Apple added the new "16-bit" audio preference setting.)

     

    In any case, see if you can play the files I posted let us know the test results.

     

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    2.66GHz 17" MBP 2.0GHz 3GB G5/533MHz 384MB G4 DeskTop/400MHz 384MB G4 Ti PB, Mac OS X (10.6.6), 60GB 5G iPod, 4GB iPhone, Nikon D-70, Nikon CoolPix 990, Sony HD
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