| Summary: | audio/x-m4b (audio/mp4 subtype) | ||
|---|---|---|---|
| Product: | shared-mime-info | Reporter: | Ed Catmur <ed> |
| Component: | freedesktop.org.xml | Assignee: | Jonathan Blandford <jrb> |
| Status: | RESOLVED FIXED | QA Contact: | |
| Severity: | normal | ||
| Priority: | medium | CC: | bugzilla, toscano.pino |
| Version: | unspecified | ||
| Hardware: | Other | ||
| OS: | All | ||
| Whiteboard: | |||
| i915 platform: | i915 features: | ||
Thanks for your bug report! It seems a bit odd that both M4A files with an M4B extension, and files with an arbitrary extension that contain a specific M4B matchlet are both treated as M4B. Is this correct? You say that M4B is a bookmarkable M4A audio file (on Apple systems), so why does it have slightly different contents at all? OK, this is more complicated than I thought. Apple, through iTMS, sells audiobooks infected with FairPlay DRM (as with their .m4p music offerings); these have M4B magic and .m4b extension. Now, iTunes will only recognise a track as an audiobook if it has an .m4b extension and is AAC in MPEG-4 (or is in Audible infected .aa format, but that's not relevant here). Because of this, providers of uninfected audiobooks (e.g. LibriVox/Gutenberg) offer AAC files with a .m4b extension but M4A magic, so that iTunes users can use them directly as audiobooks (and copy them to iPod as audiobooks): Vendor | Infected | Extn | Magic | Container | Codec | Works in iTunes ---------+--------------+------+-------+-----------+-------+---------------- iTMS | Y (FairPlay) | m4b | M4B | MPEG-4 | AAC | Y Librivox | N | m4b | M4A | MPEG-4 | AAC | Y Note that "bookmarkable" etc. is a bit of a red herring; AFAIK with iTunes/iPod the bookmark isn't stored as a tag, it's stored in the iTunes database and then written out to the iPod database. It's really about what iTunes decides to view the files as. 2007-08-31 Bastien Nocera <hadess@hadess.net> * freedesktop.org.xml.in: Add the audio/x-m4b mime-type, as a sub-class of audio/mp4 |
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Files with <match value="ftypM4B" type="string" offset="4"/> are AAC audiobook files; glob *.m4b. Also files with "ftypM4A" and glob *.m4b, renamed m4a files. The two formats are identical in terms of container, codecs etc. but iTunes allows bookmarks in m4b files, so expected application semantics are different.