[Bug 727757] atdec: Fails to decode multichannel streams

[GStreamer (bugzilla.gnome.org)]

https://bugzilla.gnome.org/show_bug.cgi?id=727757
  GStreamer | gst-plugins-bad | git

Sebastian Dröge (slomo) <slomo> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
 Attachment #279806|none                        |needs-work
             status|                            |

--- Comment #11 from Sebastian Dröge (slomo) <slomo at coaxion.net> 2014-07-03 08:21:59 UTC ---
Review of attachment 279806:
 --> (https://bugzilla.gnome.org/review?bug=727757&attachment=279806)

So let's summarize these change. What this means is that we check if downstream
wants a specific channel layout. If it does we tell AT about that and it will
produce output with exactly that channel layout in that order? So if we have a
2 channel MP3 but downstream wants 5.1, AT will upmix for us?

::: sys/applemedia/atdec.c
@@ +411,3 @@
+  if (gst_structure_get (s, "channel-mask", GST_TYPE_BITMASK,
+          &channel_mask, NULL)) {
+    gst_audio_channel_positions_from_mask (channels, channel_mask, pos);

The channel mask can have more bits set than the number of channels, even after
fixating the caps. That's a dependency between the channels and channel-mask
fields we currently can't express with our caps.

You have to check for that here, and just drop some bits (ideally on the
correct side, don't drop front left and front right but the less important
channels)

@@ +413,3 @@
+    gst_audio_channel_positions_from_mask (channels, channel_mask, pos);
+  } else {
+    memset (pos, 0, sizeof (GstAudioChannelPosition) * 64);

Note that undefined channel positions is GST_CHANNEL_POSITION_NONE and not 0

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