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Topic: Maximum Length of a Stable M4A Audiobook

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Old 05-26-2009, 03:09 AM
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Maximum Length of a Stable M4A Audiobook

I have done extensive research and have found several recommendations for the maximum length of a M4A audiobook to avoid playback problems. The problem usually results in playback stability issues such as the bookmark position being lost or the iPod skipping to the next item in your playlist while you are in the middle of a long audiobook.

The problem is very prevalent on the Video iPod (of course this is what I have) and less so on the newer iPods.

The recommendations I have found on this forum and other places are in the form of a maximum length in hours (usually less than 5 hours) and/or in the size of the file. I have found that neither length in hours or the file size appear to the main driver for the stability issues.

I have found that if the number of audio samples exceeds approximately 700 million samples, then the stability problems occur.

See the chart below of information I compiled some time ago.
Click the image to open in full size.

This means that if you limit the audiobook to 700,000,000 samples, then the length of the audiobook will be below the max length in hours listed in the table below.

Sample rate of 8.0 kHz = 24.3 hrs max
Sample rate of 12.0 kHz = 16.2 hrs max
Sample rate of 16.0 kHz = 12.2 hrs max
Sample rate of 22.05 kHz = 8.8 hrs max
Sample rate of 24.0 kHz = 8.1 hrs max
Sample rate of 32.0 kHz = 6.1 hrs max
Sample rate of 44.1 kHz = 4.4 hrs max
Sample rate of 48.0 kHz = 4.1 hrs max


I normally encode my audiobooks as mono with a bitrate of 16kbs and at a sample rate of 12.0 kHz. Using these import settings in iTunes I can create audiobooks that are slightly over 16 hours long without playback issues.

I use the "Chapter & Verse" audiobook creation software I created which is available on my website (lodensoftware . com)

Hopefully this will be of use to those of you looking to maximize the size of your audiobook without needing to split it into multiple parts.
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Old 09-23-2009, 10:25 AM
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I'm not sure why, but I can't edit my old posts...

UPDATE:

I have found that if the number of audio samples exceeds approximately 650 million samples, then the stability problems occur.

This translates into the following maximum lengths.

Sample rate of 8.0 kHz = 22.6 hrs max
Sample rate of 12.0 kHz = 15.0 hrs max
Sample rate of 16.0 kHz = 11.3 hrs max
Sample rate of 22.05 kHz = 8.2 hrs max
Sample rate of 24.0 kHz = 7.5 hrs max
Sample rate of 32.0 kHz = 5.6 hrs max
Sample rate of 44.1 kHz = 4.1 hrs max
Sample rate of 48.0 kHz = 3.8 hrs max
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Old 10-14-2009, 08:40 PM
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how do you change the sample rate when converting in itunes?


also, are you now using a classic? can you verify whether or not these problems persist there?

thanks
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Old 10-16-2009, 10:36 PM
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crash613

Changing the sample rate on iTunes

Select the Edit --> Preferences Menu Item
Select the General Tab
Click on the "Import Settings ..." button
Change "Import Using" dropdown to "AAC Encoder"
Click on "Setting" dropdown and choose "Custom..."
The AAC Encoder settings dialog will pop up

On the AAC Encoder settings dialog you will see a bunch of settings including a setting for the sample rate.


I can't confirm whether the problem is fixed or not, since I have a 30GB video iPod.
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Old 10-17-2009, 07:39 AM
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hum.... i have itunes 7 and it only gives you the choice os 44.1 or 48.0.... no other choices
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Old 12-14-2009, 03:18 PM
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Red face Continued bookmarking problems

Does this mean that almost all audiobooks fall into this category. Most are pretty long. I am a real novice at this. IS THERE A QUICK NON-TECHY FIX?
This translates into the following maximum lengths.

Sample rate of 8.0 kHz = 22.6 hrs max
Sample rate of 12.0 kHz = 15.0 hrs max
Sample rate of 16.0 kHz = 11.3 hrs max
Sample rate of 22.05 kHz = 8.2 hrs max
Sample rate of 24.0 kHz = 7.5 hrs max
Sample rate of 32.0 kHz = 5.6 hrs max
Sample rate of 44.1 kHz = 4.1 hrs max
Sample rate of 48.0 kHz = 3.8 hrs max[/QUOTE]
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Old 12-15-2009, 09:36 AM
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There is no "FIX" for this.

You can work around it though.

1. Import each audiobook CD as a single file (select all the tracks, click on Advanced->Join CD tracks) at spoken podcast quality.
2. Modify each audiobook file to have Remember Playback Position and Skip On Shuffle.
3. Create a smart or standard playlist that has the whole book. (CD - Audiobook)
4. Create a smart playlist that has the Playlist of the whole audiobook, and Playcount is 0. (Audiobook)
5. Sync both playlists.

When you want to listen find the Audiobook playlist and play. It will remember which disk you were on and where in that disc you were.

When you want to "reset" the book, go to the CD - Audiobook playlist, select all the tracks, right click one of them and choose Reset Playcount and answer Yes.

Don't bother trying to combine audiobooks into one file. If you do, then use the chart you quoted to determine the maximum length you can go based on the quality you use to import.



Have you backed up your iTunes Library this week? If not, you are risking losing your music and playlists....
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Old 12-16-2009, 05:40 PM
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cjmnews is right that there is no fix for this. Apple would have to update the firmware for their older iPods to fix this ... that assumes they can fix it. No one knows the exact cause except Apple.

It may not be clear from the chart I posted above, but Audible, Apple's audiobook partner, limits the length of their audiobooks to within the limit I listed above (see green markers on chart).

My quick non- techy solution is to reduce your sample rate and/or split your audiobook into mulitple parts.

Apple now provides a range of sample rates in iTunes 9+ that you can select directly under the AAC Encoder custom settings. If you're using iTunes 7... then upgrade.

My default audiobook settings are:
Stereo bitrate: 32 kbps (16kbps mono)
Sample rate : 12 kHz
Channels: mono

With these settings, the average unabridged audio can be a single file (i.e. less than 15 hours).
For longer audiobooks you can split them into 2 parts. Very few audiobooks are longer than 30 hours.

I would still rather have an audiobook in 2 parts with chapters than have 10 to 20 files (if tracks joined so one file per disc) or 120 to 250 individual tracks.

Last edited by jloden; 12-16-2009 at 06:25 PM.
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Old 12-16-2009, 05:51 PM
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thanks for the advice but as has been discussed way before Jan 2009 there were many problems that led to my decision to stay with itunes 7. I'll have to find another way. not "upgrading" to itunes9
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Old 12-16-2009, 06:34 PM
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If you don't want to upgrade, I believe you can still achieve the same result if you select the following custom settings in iTunes 7:

Stereo bitrate: 32 kbps (16kbps mono)
Sample rate : Auto
Channels: mono

Selecting the "Auto" setting for sample rate with the other settings above, iTunes uses a sample rate of 12 kHz.

If you vary the bitrate and leave the sample rate setting on Auto", iTunes will vary the sample rate with the bitrate. You won't have direct control, but you can get more than the 44.1 and 48 kHz settings. You'll have to use trial and error to see what iTunes selects for a sample rate given the bitrate.

If you want more control over your sample rate then that and don't want to upgrade, then you will need to use another program that uses the Nero encoder or FAAC.

Last edited by jloden; 12-16-2009 at 06:41 PM.
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Old 01-28-2010, 04:46 PM
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What would be upgrade recommendation to fix?

Hello there.

I was very glad to find this post. I have been fighting this 'lost bookmark' problem for a while and it is driving me nuts. I can't stand dealing with multiple tracks, but it seems like that's what I'm left with on the very large books. However, I'm seeing the problem show up on large tracks that are still relatively small and even fit within the specs you've listed.

However...I AM using an old 5Gen video ipod. So I'm guessing that doesn't help the situation.

You mention that the newer iPod models handle this problem a little better (though not perfectly). If that is indeed true then it is worth upgrading.

So here's my question...if I were to upgrade for the sole purpose of making this 'large audiobook' problem better, is there a particular model anyone would recommend? I need at least 80GB and that's about all that really matters to me (besides improving the audiobook problem).

Thoughts?
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Old 01-29-2010, 12:22 PM
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I have not heard of a model of iPod that can handle it any better than the one you have.

They are all limited. Upgrading for the large audiobooks is not a good reason to upgrade. Upgrading for capacity, or camera or tilt screen would be a better reason to upgrade.



Have you backed up your iTunes Library this week? If not, you are risking losing your music and playlists....
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