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Subject: Re: Bring me your broken MP4s, your twitchy AACs and other non-working m4a's

Re: Bring me your broken MP4s, your twitchy AACs and other non-working m4a's

From: Alex Bennee <>
Date: Wed, 6 May 2009 09:00:27 +0100

2009/5/6 Vladimir Pantelic <>:
> Alex Bennee wrote:
>> Hi,
>> I've been working on a patch (FS#10160) to get some m4a files I own to
> <snip>
> moov after mdat is not uncommon at all. Some MP4 writer SW do that so
> they can 1st write all the data, then add the "header" at the end. Of
> course that messes up streaming such files....

This file was from iTunes although curiously the others in the same
album didn't have this moov after mdat layout. As it stands Rockbox
(with my patch) will now play these files.

>> I could take this as a quick win, redefine the code to only deal with
>> single mdat's but parse the whole file before starting. However there
>> is nothing in the MP4 container spec that says files can't have
>> multiple "mdat" atoms.
> Yes, in theory you could have each "sample" inside it's own mdat if you
> wanted.

That would be pathalogical. At the moment I've a fixed size array in
the codec that will deal with up to 10 mdat atoms in a file. As we
can't really dynamically allocate re-sizeable memory I think the best
that can be done is size it according to what has been seen in the wild.

>> So do you have any mp4, m4a or other mp4-alike file that won't play
>> with the rockbox libm4a codec? If so could you send me a copy?
> there is the ffmpeg/mplayer samples database, maybe they have something.
> (

I shall have a look. Thanks.

Alex, homepage:
Received on 2009-05-06

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