Re: [Rhythmbox-devel] Writing m4a tags

[Jonathan Matthew <jonathan d14n org>]

On Sat, Nov 01, 2008 at 05:34:51PM -0400, Ryan Hughes wrote:
> Hi.  When I use rhythmbox, I don't seem to be able to write tags in m4a  
> files.  I'm trying to look up information about this, but the 
> signal/noise ratio is very low.  I'm seeing posts from 2005 about reading 
> tags, I'm seeing posts about not being able to play m4a files at all.  
> I'm seeing things about taglib, easytag, and faad.  I'm seeing things 
> about amarok.
>
> So I'd like to get the answers straight from the horse's mouth:
>
> What's the deal with writing m4a tags in rhythmbox?

To get tag editing working in rhythmbox for any given format, you need
two things:
- GStreamer elements that can be used to construct a pipeline that
  rewrites the tags without re-encoding the audio
- code in rhythmbox to construct that pipeline

For m4a, the former more or less exists, but the latter does not.
The retagging pipeline seems to be just 'src ! qtdemux ! ffmux_mp4 !
sink'.  GStreamer developers usually tell people not to use ffmpeg
muxers, as they often have bugs and it's difficult to fix them, so I'd
be a bit nervous about using this pipeline in rhythmbox where it could
corrupt the user's files.

The qtmux plugin for GStreamer
(http://gforge.embedded.ufcg.edu.br/projects/qtmux/) should provide a
better supported way to do this, but I'm not sure if it's ready for
general use yet.  If you want to help out somewhere, this is probably
the place to do it.

The rhythmbox side of things is pretty simple.  I've just put together a
patch that should do it, and once I've done some basic testing I'll
commit it.