I'm using -ac ffwmav2. At several places in this file, the audio decoding freezes the playback (the numbers at the bottom keep rolling, but no more video or audio can be seen/heard).

An easy test command is:
mplayer video_stops.avi -ss 115 -ac ffwmav2
This will jump to a few seconds before the first part that has a problem. Other instances can be found throughout the file, such as near seconds 400, 710, and 740.

When I use -ac null, the video playback continues. -ac divx plays the file without a problem.

----------------------------------------
Details:

mplayer CVS from about an hour ago (though the problem has been around for a while).

Debian Sarge (all up-to-date)

Linux bugfood 2.4.20-pre10-ac1 #1 Sun Oct 13 19:00:34 PDT 2002 i686 AMD Athlon(tm) XP 2200+ AuthenticAMD GNU/Linux

bugfood@bugfood:~$ ls -l /lib/libc[.-]*
-rwxr-xr-x    1 root     root      1145456 Sep 17 19:50 /lib/libc-2.2.5.so
lrwxrwxrwx    1 root     root           14 Oct  4 03:52 /lib/libc.so.5 -> libc.so.5.4.46
-rw-r--r--    1 root     root       563068 Feb  4  2002 /lib/libc.so.5.4.46
lrwxrwxrwx    1 root     root           13 Nov  6 18:00 /lib/libc.so.6 -> libc-2.2.5.so

bugfood@bugfood:~$ X -version

XFree86 Version 4.2.1 (Debian 4.2.1-3 20021016191246 branden@deadbeast.net) / X Window System
(protocol Version 11, revision 0, vendor release 6600)
Release Date: 3 September 2002
	If the server is older than 6-12 months, or if your card is
	newer than the above date, look for a newer version before
	reporting problems.  (See http://www.XFree86.Org/)
	Build Operating System: Linux 2.4.18 i686 [ELF] 
	Module Loader present

bugfood@bugfood:~$ gcc -v
Reading specs from /usr/lib/gcc-lib/i386-linux/2.95.4/specs
gcc version 2.95.4 20011002 (Debian prerelease)

bugfood@bugfood:~$ ld -v
GNU ld version 2.13.90.0.10 20021010 Debian GNU/Linux

bugfood@bugfood:~$ as --version
GNU assembler 2.13.90.0.10 20021010 Debian GNU/Linux
Copyright 2002 Free Software Foundation, Inc.
This program is free software; you may redistribute it under the terms of
the GNU General Public License.  This program has absolutely no warranty.
This assembler was configured for a target of `i386-linux'.

------------------------------------------

bugfood@bugfood:/tmp/bug$ mplayer video_stops.avi -ss 120 -ac ffwmav2 -frames 25 -v
Using GNU internationalization
Original domain: messages
Original dirname: /usr/share/locale
Current domain: mplayer
Current dirname: /usr/local/share/locale


MPlayer CVS-021210-17:16-2.95.4 (C) 2000-2002 Arpad Gereoffy (see DOCS)

CPU: Advanced Micro Devices  (Family: 6, Stepping: 0)
CPUflags:  MMX: 1 MMX2: 1 3DNow: 1 3DNow2: 1 SSE: 1 SSE2: 0
Compiled for x86 CPU with extensions: MMX MMX2 3DNow 3DNowEx SSE

Reading config file /usr/local/etc/mplayer/mplayer.conf: No such file or directory
Reading config file /home/bugfood/.mplayer/config
Reading /home/bugfood/.mplayer/codecs.conf: 49 audio & 123 video codecs
CommandLine: 'video_stops.avi' '-ss' '120' '-ac' 'ffwmav2' '-frames' '25' '-v'
get_path('font/font.desc') -> '/home/bugfood/.mplayer/font/font.desc'
Font /home/bugfood/.mplayer/font/font.desc loaded successfully! (206 chars)
Using MMX (with tiny bit MMX2) Optimized OnScreenDisplay
Failed to open /dev/rtc: Permission denied (mplayer should be setuid root or /dev/rtc should be readable by the user.)
Using usleep() timing
get_path('input.conf') -> '/home/bugfood/.mplayer/input.conf'
Parsing input config file /home/bugfood/.mplayer/input.conf
Input config file /home/bugfood/.mplayer/input.conf parsed : 57 binds
Opening joystick device /dev/input/js0

Playing video_stops.avi
Not an URL!
File size is 85007696 bytes
Checking for YUV4MPEG2
DEMUXER: freeing demuxer at 0x8406b30  
Detected ASF file format!
ASF: packets: 12971  flags: 2  max_packet_size: 6553  min_packet_size: 6553  max_bitrate: 524288  preroll: 3199

 Title: The Simpsons S11E5
 Author: {FoW} - FarGGen -
 Copyright: #movie-lounge on dalnet
 Comment: 
 Rating: (None)

stream type: guid_audio_stream
stream concealment: guid_audio_conceal_interleave
type: 28 bytes,  stream: 8 bytes  ID: 1
unk1: 0  unk2: 1FBEFD0
FILEPOS=0x1AE
==> Found audio stream: 1
======= WAVE Format =======
Format Tag: 353 (0x161)
Channels: 2
Samplerate: 22050
avg byte/sec: 4005
Block align: 744
bits/sample: 16
cbSize: 10
Unknown extra header dump: [0] [80] [0] [0] [17] [0] [40] [17] [0] [0] 
ASF: audio scrambling: 1 x 1 x 744
stream type: guid_video_stream
stream concealment: unknown guid 0057fb20-555b-cf11-a8fd00805f5c442b
type: 51 bytes,  stream: 0 bytes  ID: 2
unk1: 0  unk2: 1FBEFD0
FILEPOS=0x220
==> Found video stream: 2
======= VIDEO Format ======
  biSize 40
  biWidth 320
  biHeight 240
  biPlanes 1
  biBitCount 24
  biCompression 842289229='MP42'
  biSizeImage 230400
===========================
Found movie at 0x367 - 0x510FE9A
ASF: 1 audio and 1 video streams found
Invalid plen type! assuming plen=0
Auto-selected ASF audio ID = 1
Auto-selected ASF video ID = 2
VIDEO:  [MP42]  320x240  24bpp
ASF: Searching for audio stream (id:1)
Invalid plen type! assuming plen=0
[V] filefmt:6  fourcc:0x3234504D  size:320x240  fps:1000.00  ftime:=0.0010
Clip info: 
 name: The Simpsons S11E5
 author: {FoW} - FarGGen -
 copyright: #movie-lounge on dalnet
 comments: 
get_path('sub/') -> '/home/bugfood/.mplayer/sub/'
==========================================================================
Forced audio codec: ffwmav2
Opening audio decoder: [ffmpeg] FFmpeg/libavcodec audio decoders
dec_audio: Allocating 131072 + 65536 = 196608 bytes for output buffer
FFmpeg's libavcodec audio codec
INFO: libavcodec init OK!
AUDIO: 22050 Hz, 2 ch, 16 bit (0x10), ratio: 4005->88200 (32.0 kbit)
Selected audio codec: [ffwmav2] afm:ffmpeg (DivX audio v2 (ffmpeg))
==========================================================================
X11 opening display: :0
vo: X11 color mask:  FFFFFF  (R:FF0000 G:FF00 B:FF)
vo: X11 running at 1280x1024 with depth 24 and 32 bpp (":0" => local display)
==========================================================================
Opening video decoder: [ffmpeg] FFmpeg's libavcodec codec family
INFO: libavcodec init OK!
Selected video codec: [ffmp42] vfm:ffmpeg (FFmpeg M$ MPEG-4 v2)
==========================================================================
ao2: 22050 Hz  2 chans  Signed 16-bit (Little-Endian)
audio_setup: using '/dev/sound/dsp' dsp device
audio_setup: sample format: Signed 16-bit (Little-Endian) (requested: Signed 16-bit (Little-Endian))
audio_setup: using 2 channels (requested: 2)
audio_setup: using 22050 Hz samplerate (requested: 22050)
audio_setup: frags:  16/16  (8192 bytes/frag)  free: 131072
AO: [oss] 22050Hz 2ch Signed 16-bit (Little-Endian)
AO: Description: OSS/ioctl audio output
AO: Author: A'rpi
Building audio filter chain for 22050Hz/2ch/16bit -> 22050Hz/2ch/16bit...
Adding filter dummy 
[dummy] Was reinitialized, rate=22050Hz, nch = 2, format = 0x00000001 and bps = 2
[dummy] Was reinitialized, rate=22050Hz, nch = 2, format = 0x00000001 and bps = 2
Start playing...
Invalid plen type! assuming plen=0
Invalid plen type! assuming plen=0
Invalid plen type! assuming plen=0
Invalid plen type! assuming plen=0
Invalid plen type! assuming plen=0

avg. framerate: 15 fps             
VDec: vo config request - 320 x 240 (preferred csp: Planar YV12)
VDec: using Planar YV12 as output csp (no 0)
Movie-Aspect is undefined - no prescaling applied.
VO Config (320x240->320x240,flags=0,'MPlayer',0x32315659)
VO: [xv] 320x240 => 320x240 Planar YV12 
VO: Description: X11/Xv
VO: Author: Gerd Knorr <kraxel@goldbach.in-berlin.de> and others
Xvideo image format: 0x32595559 (YUY2) packed
Xvideo image format: 0x32315659 (YV12) planar
Xvideo image format: 0x59565955 (UYVY) packed
Xvideo image format: 0x30323449 (I420) planar
using Xvideo port 119 for hw scaling
[xv] dx: 0 dy: 0 dw: 320 dh: 240
*** [vo] Allocating mp_image_t, 320x240x12bpp YUV planar, 115200 bytes
[xv] dx: 0 dy: 0 dw: 320 dh: 240
Invalid plen type! assuming plen=0 0.000    1/  1   0%  0%  0.0% 0 0 0%
Invalid plen type! assuming plen=0
Invalid plen type! assuming plen=0
Invalid plen type! assuming plen=0
Invalid plen type! assuming plen=0
Invalid plen type! assuming plen=0
Invalid plen type! assuming plen=0
Invalid plen type! assuming plen=0
Invalid plen type! assuming plen=0
*** [vo] Allocating mp_image_t, 320x240x12bpp YUV planar, 115200 bytes
Invalid plen type! assuming plen=0 0.009    2/  2   0%  0%  0.0% 0 0 0%
Invalid plen type! assuming plen=0
Invalid plen type! assuming plen=0
Invalid plen type! assuming plen=0
Invalid plen type! assuming plen=0
lavc_audio: error
Invalid plen type! assuming plen=0
Invalid plen type! assuming plen=0
lavc_audio: error
Invalid plen type! assuming plen=0
Invalid plen type! assuming plen=0
lavc_audio: error
Invalid plen type! assuming plen=0 0.015    3/  3   0%  0%  0.0% 0 0 0%
Invalid plen type! assuming plen=0
lavc_audio: error
Invalid plen type! assuming plen=0 0.022    4/  4   0%  0%  0.0% 0 0 0%
Invalid plen type! assuming plen=0
lavc_audio: error
Invalid plen type! assuming plen=0 0.029    5/  5   0%  0%  0.0% 0 0 0%
Invalid plen type! assuming plen=0
lavc_audio: error
Invalid plen type! assuming plen=0 0.035    6/  6   0%  0%  0.0% 0 0 0%
lavc_audio: error
Invalid plen type! assuming plen=0 0.042    7/  7   0%  0%  0.0% 0 0 0%
Invalid plen type! assuming plen=0
lavc_audio: error
Invalid plen type! assuming plen=0 0.049    8/  8   0%  0%  0.0% 0 0 0%
Invalid plen type! assuming plen=0
lavc_audio: error
Invalid plen type! assuming plen=0 0.055    9/  9   1%  1%  3.6% 0 0 0%
Invalid plen type! assuming plen=0
lavc_audio: error
Invalid plen type! assuming plen=0 0.062   10/ 10   1%  1%  3.2% 0 0 0%
Invalid plen type! assuming plen=0
lavc_audio: error
Invalid plen type! assuming plen=0 0.069   11/ 11   1%  1%  2.9% 0 0 0%
Invalid plen type! assuming plen=0
lavc_audio: error
Invalid plen type! assuming plen=0 0.075   12/ 12   1%  1%  2.6% 0 0 0%
Invalid plen type! assuming plen=0
lavc_audio: error
Invalid plen type! assuming plen=0 0.082   13/ 13   1%  1%  2.4% 0 0 0%
Invalid plen type! assuming plen=0
lavc_audio: error
Invalid plen type! assuming plen=0 0.089   14/ 14   1%  1%  2.3% 0 0 0%
lavc_audio: error
Invalid plen type! assuming plen=0 0.095   15/ 15   1%  1%  2.1% 0 0 0%
Invalid plen type! assuming plen=0
lavc_audio: error
Invalid plen type! assuming plen=0 0.102   16/ 16   1%  1%  2.0% 0 0 0%
Invalid plen type! assuming plen=0
lavc_audio: error
Invalid plen type! assuming plen=0 0.105   17/ 17   1%  1%  1.9% 0 0 0%
Invalid plen type! assuming plen=0
lavc_audio: error
Invalid plen type! assuming plen=0 0.105   18/ 18   1%  1%  1.8% 0 0 0%
Invalid plen type! assuming plen=0
lavc_audio: error
Invalid plen type! assuming plen=0 0.105   18/ 18   1%  1%  1.8% 0 0 0%
Invalid plen type! assuming plen=0
lavc_audio: error
Invalid plen type! assuming plen=0 0.105   18/ 18   1%  1%  1.8% 0 0 0%
Invalid plen type! assuming plen=0
lavc_audio: error
Invalid plen type! assuming plen=0 0.105   18/ 18   1%  1%  1.8% 0 0 0%
Invalid plen type! assuming plen=0
lavc_audio: error
Invalid plen type! assuming plen=0 0.105   18/ 18   1%  1%  1.8% 0 0 0%
lavc_audio: error
Invalid plen type! assuming plen=0 0.105   18/ 18   1%  1%  1.9% 0 0 0%
Invalid plen type! assuming plen=0
lavc_audio: error
Invalid plen type! assuming plen=0 0.105   18/ 18   1%  1%  1.9% 0 0 0%
Invalid plen type! assuming plen=0
lavc_audio: error
Invalid plen type! assuming plen=0 0.105   18/ 18   1%  1%  1.9% 0 0 0%
Invalid plen type! assuming plen=0
lavc_audio: error
EOF code: 1  25.0 A-V:  4.981 ct:  0.105   18/ 18   1%  1%  1.9% 0 0 0%

Uninit audio filters...
uninit audio: ffmpeg  
uninit video: ffmpeg  
DEMUXER: freeing demuxer at 0x8406b30  
DEMUXER: freeing sh_audio at 0x8403428  
DEMUXER: freeing sh_video at 0x84034f0  
vo: uninit ...

Exiting... (End of file)