• Status Unconfirmed
  • Percent Complete
  • Task Type Bugs
  • Category Codecs
  • Assigned To No-one
  • Operating System iPod 4G Grayscale
  • Severity Medium
  • Priority Very Low
  • Reported Version Daily build (which?)
  • Due in Version Undecided
  • Due Date Undecided
  • Votes
  • Private
Attached to Project: Rockbox
Opened by 20esproductions - 2020-10-25
Last edited by 20esproductions - 2020-10-27

FS#13251 - Playback stutters when playing Apple .m4a files

When a .m4a file is played, particularly one bought from the iTunes store, it seems to overwhelm the AAC codec in rockbox.

I think it may be something to do with the ‘anti-skip buffer’ but I cannot confirm this for sure, but it seems related, as in the stable release (3.15) playback works fine and the HDD Access indicator in the corner is only displayed briefly during the beginning of playback. In the latest development build (Rev. 3fbca49) and a few previous, however, the HDD access indicator stays on screen at all times during stuttery playback, the whole system becomes slow and almost impossible to use and sometimes locks up completely.

I have confirmed this on my iPod 4G color, it seems to be only on older iPods, as my 6th Gen classic plays them fine!

IMPORTANT NOTE: I am using an iFlash solo + 128GB SD in the iPod. Haas surround 5ms is enabled along with +3db tone control on both bass and treble


Can you try older daily builds to see if there is a clear point where things started to malfunction?

I'd start with the oldest (9-28 as I write this), and jump forward one week at a time..


Also, the hw being accessed would cause anything to stutter, but it's not immediately clear how the codec would affect that.

For sanity's sake, can you do a chkdsk (or equivalent) on the ipod to make sure there's nothing amiss?

I updated the report with some info to consider, whilst I test this some more

I ran a chkdsk on it as soon as I noticed the issue and all was clear

It definitely has something to do with Haas Surround being enabled

The m4a I am using to test is the Extended mix of 'Scatman' by Scatman John, purchased from the iTunes store.
The file has a Variable bit rate of around 281kbit.
I am using the Rockbox failsafe theme.
The issue affects iPod Color, too, regardless of original Apple hard disk, or iFlash adaptor. Anti- skip buffer is set to 10:00 in playback settings.

If you want the exact .m4a file I am using, please, feel free to ask!

Haas surround and tone controls are enabled, as outlined above

Here are my results:

  • Rev. 018e005 - plays fine
  • Rev. 977a03a - Plays fine
  • Rev. a511917 - Plays fine
  • Rev. cb9b5d3 - plays fine
  • Rev. b5cb99a - plays fine
  • Rev. 1824f8b - plays fine
  • Rev. f3ae48f - plays fine
  • Rev. 74258fc - plays fine
  • Rev. 914114f - plays fine
  • Rev. cb9280c - plays fine
  • Rev. 2e2e899 - plays fine
  • Rev. 7a1bf01 - plays fine - in my particular case, instead of taking around 50secs for the drive access indicator to disappear it disappeared in around 17s!
  • Rev. 7c00e9b - plays fine
  • Rev. 4f87369 - plays fine
  • Rev. 135b3f6 - plays fine
  • Rev. f68463c - plays fine
  • Rev. 19d45c9 - STUTTERS play/pause/play/pause… and so on.. Disk indicator does not disappear, either. Plays perfectly with Haas surround disabled, tone controls enabled. I turned off tone controls and JUST Haas surround and it still stutters. Haas off, tone off, plays fine. Tone controls on, no haas, plays fine.
  • Rev. ca4d63d - STUTTERS

I find it usually stutters within the first 10 seconds of the song. I think 'temporarily freezing' might actually be a better term for this.

I hope this information proves to be useful! :)


Okay, pretty sure the change in behavior was triggered by the toolchain bump.

Can you please try the latest dev build, and see if the stuttering is still present? If it is, I will probably need you to send me the file that demonstrates the problem so I can directly test things.


the stuttering/skipping is still present in the latest dev build. Here is the m4a, as you requested.


Using the latest dev build on my mini2g (same hw generation as the 4g greyscale) I'm unable to recreate any stuttering. Hmm.

are you using the same settings?


that's a very good point! Can you attach your config file so I can be sure I'm using the same settings?

this should do it - from my .rockbox folder on my iPod 4G color - the greyscale one is at home at the minute, but both these devices were experiencing the issue.

I have this problem with my iPod Mini 2nd generation. I have it with both today's development version and the 3.15 release version however.


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