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

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

From: Alex Bennee <>
Date: Wed, 6 May 2009 08:19:17 +0100


I've been working on a patch (FS#10160) to get some m4a files I own to
play on Rockbox. Originally it looked as though the problem was
Rpckbox's limitation on only being able to handle files with a single
"mdat" atom containing data for the codec. Some I dug into the code
and started adding support for this case.

As it happens although the test file in question has two "mdat" atoms
the second one is of zero length (probably a placeholder). However the
reason the file wasn't playing is because additional information
needed to start playback (in the "moov" atom) is after the main "mdat"
atom where rockbox used to stop parsing the file.

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. However I'm suffering a lack of good test cases
to work with.

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?

Even better would be if anyone could tell me the command line foo to
generate such a multi-chucked mp4 file so I can make my own test

In the meantime the code is in Flyspray for your comments
( It currently has one very
un-handled case in it (the FIXME) and quite a lot of enabled DEBUGFs
which will need to be cleaned up before final submission. However
comments are always welcome.

Alex, homepage:
Received on 2009-05-06

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