[gst-devel] gst-ffmpeg & decodebin

[Michael Smith]

On Wed, 2008-02-06 at 16:33 +0100, Tom Cooksey wrote:
> Hi,
> 
> Background: I am trying to get the new Qt/KDE Phonon library working on Qtopia 
> Core (Qt/Embedded). Linux/Qtopia Core uses the GStreamer backend for Phonon - 
> specifically the decodebin element.
> 
> I'm having problems getting decodebin (& playbin) to detect & use the ffmpeg 
> elements. E.g.
> 
> The following works fine:
> gst-launch filesrc location=01_Neighborhood_1_Tunnels_.mp3  ! ffdemux_mp3 ! 
> ffdec_mp3 ! alsasink
> 
> However, using decodebin I get:
> 
> $ gst-launch-0.10 filesrc location=01_Neighborhood_1_Tunnels_.mp3 ! 
> decodebin ! audioconvert ! alsasink

The key difference between these two is that decodebin will only
autoplug elements that have a non-zero rank.

ffdemux_mp3 and ffdec_mp3 have zero rank, because they don't work
properly and there are better ones available in gstreamer. So they're
there, and you can explicitly use them if you want, but we strongly
recommend against it.

gst-plugins-ugly contains a number of mp3-related plugins (including 
mpegaudioparse and mad, which are probably the ones you want).

> 
> Questions:
> 1) Has this already been fixed? I'm using gst-ffmpeg 10.3.

This is not a bug, as described above.

> 2) If not, is it worth debuging this & sending in a patch? Would it ever be 
> accepted? I smell patent politics with this bug. Specifically, gstreamer 
> should prefer a patent-free plugin over a plugin which has a merky patent 
> status.

This isn't patent politics - it's simply a matter of what works. ffmpeg and 
the other mp3-related plugins have exactly the same legal issues, so if you
want to use EITHER of them, you'll have to sort that out, but the ffmpeg mp3 
decoder just doesn't work well enough.

Mike