mkfifo video.pipe
mkfifo audio.pipe
mkfifo audio2.pipe

mkvmerge -o 66.mkv video.pipe audio2.pipe & mencoder 66.mpg -nosound -ovc lavc -lavcopts vcodec=mpeg4:vbitrate=1500:mpeg_quant:autoaspect -o video.pipe & oggenc -b 160 -o audio2.pipe audio.pipe & mplayer -vc null -vo null -ao pcm:fast:file=audio.pipe 66.mpg

The output:

Encoder dev-CVS-060515-22:14-3.4.6 (C) 2000-2006 MPlayer Team
CPU: Advanced Micro Devices Athlon 64 Clawhammer; Athlon 64 X2 Toledo; Turion Newark,Lancaster (Family: 15, Stepping: 10)
CPUflags: Type: 15 MMX: 1 MMX2: 1 3DNow: 1 3DNow2: 1 SSE: 1 SSE2: 1
Compiled for x86 CPU with extensions: MMX MMX2 3DNow 3DNowEx SSE SSE2

MPlayer dev-CVS-060515-22:14-3.4.6 (C) 2000-2006 MPlayer Team
CPU: Advanced Micro Devices Athlon 64 Clawhammer; Athlon 64 X2 Toledo; Turion Newark,Lancaster (Family: 15, Stepping: 10)
CPUflags:  MMX: 1 MMX2: 1 3DNow: 1 3DNow2: 1 SSE: 1 SSE2: 1
Compiled for x86 CPU with extensions: MMX MMX2 3DNow 3DNowEx SSE SSE2

WARNING: OUTPUT FILE FORMAT IS _AVI_. See -of help.
mkvmerge v1.6.5 ('Watcher Of The Skies') built on Mar 19 2006 23:11:32

success: format: 0  data: 0x0 - 0x2465800

Playing 66.mpg.
MPEG-PS file format detected.
VIDEO:  MPEG1  720x576  (aspect 3)  25.000 fps    0.0 kbps ( 0.0 kbyte/s)
[V] filefmt:2  fourcc:0x10000001  size:720x576  fps:25.00  ftime:=0.0400

Error: The source file 'video.pipe' could not be opened successfully, or retrieving its size by seeking to the end did not work.
MPEG-PS file format detected.
VIDEO:  MPEG1  720x576  (aspect 3)  25.000 fps    0.0 kbps ( 0.0 kbyte/s)
==========================================================================
Opening audio decoder: [mp3lib] MPEG layer-2, layer-3
AUDIO: 48000 Hz, 2 ch, s16le, 64.0 kbit/4.17% (ratio: 8000->192000)
Selected audio codec: [mp3] afm: mp3lib (mp3lib MPEG layer-2, layer-3)
==========================================================================
Opening video filter: [expand osd=1]
Expand: -1 x -1, -1 ; -1, osd: 1, aspect: 0.000000, round: 1
==========================================================================
==========================================================================
Forced video codec: null
Opening video decoder: [null] Null video decoder
VDec: vo config request - 720 x 576 (preferred colorspace: BGR 24-bit)
VDec: using Planar YV12 as output csp (no 0)
Movie-Aspect is undefined - no prescaling applied.
VO: [null] 720x576 => 720x576 Planar YV12
Selected video codec: [null] vfm: null (NULL codec (no decoding!))
==========================================================================
[AO PCM] File: audio.pipe (WAVE)
PCM: Samplerate: 48000Hz Channels: Stereo Format s16le
[AO PCM] Info: Faster dumping is achieved with -vc null -vo null -ao pcm:fast
[AO PCM] Info: To write WAVE files use -ao pcm:waveheader (default).
AO: [pcm] 48000Hz 2ch s16le (2 bytes per sample)
Starting playback...
Opening with wav module: WAV file reader
Opening video decoder: [mpegpes] MPEG 1/2 Video passthrough,?% 1 0
VDec: vo config request - 720 x 576 (preferred colorspace: Mpeg PES)
Could not find matching colorspace - retrying with -vf scale...
Opening video filter: [scale]
The selected video_out device is incompatible with this codec.
Try adding the scale filter, e.g. -vf spp,scale instead of -vf spp.
VDecoder init failed :(
Opening video decoder: [libmpeg2] MPEG 1/2 Video decoder libmpeg2-v0.4.0b
Selected video codec: [mpeg12] vfm: libmpeg2 (MPEG-1 or 2 (libmpeg2))
==========================================================================
VDec: vo config request - 720 x 576 (preferred colorspace: Planar YV12)
VDec: using Planar YV12 as output csp (no 0)
Movie-Aspect is 1.78:1 - prescaling to correct movie aspect.
videocodec: libavcodec (720x576 fourcc=34504d46 [FMP4])
Writing header...2f ( 0%)  0.00fps Trem:   0min   0mb  A-V:0.000 [0:0]
ODML: vprp aspect is 16:9.
Writing header...
ODML: vprp aspect is 16:9.

1 duplicate frame(s)!
video.pipe: Error writing file.fps Trem:   1min   0mb  A-V:0.000 [0:0]

Exiting...


MPlayer interrupted by signal 2 in module: play_audio