Summary and Info:

When attempting to playback 6-channel audio, mplayer cannot initialize alsa.


Steps to Reproduce:

Playback any file with 6-channel audio. No sound is heard, and no audio decoder is selected, as shown in smplayer's Information Window.

Here is a portion of the relevant mplayer log:

MPlayer SVN-r31428-4.5.0 (C) 2000-2010 MPlayer Team
154 audio & 339 video codecs

Playing T2_720.wmv.

==========================================================================
Opening audio decoder: [ffmpeg] FFmpeg/libavcodec audio decoders
AUDIO: 48000 Hz, 6 ch, floatle, 384.0 kbit/4.17% (ratio: 48000->1152000)
ID_AUDIO_BITRATE=384000
ID_AUDIO_RATE=48000
ID_AUDIO_NCH=6
Selected audio codec: [ffwmapro] afm: ffmpeg (WMA Pro audio (FFmpeg))
==========================================================================
[AO_ALSA] alsa-lib: pcm_hw.c:448:(snd_pcm_hw_sw_params) SNDRV_PCM_IOCTL_SW_PARAMS failed (-22): Invalid argument
[AO_ALSA] Unable to get sw-parameters: Invalid argument
Failed to initialize audio driver 'alsa'
Could not open/initialize audio device -> no sound.
Audio: no sound
Starting playback...

Apart from this package here, I have tested numerous mplayer svn revision, both older and newer, all built with the same configure options. Behavior remains the same.

And because this started around the time kernel 2.6.34 moved from testing to core, I suspect it has to do with the alsa contained in the new kernel.