What am I doing wrong here in Mencoder?

Here's basically what I'm attempting to do - convert .mkv to .avi

Here's the command(s) I used:
here's the first one I tried, which worked - but had no sound at all:

    $ mencoder Immortals.2011.720p.BRRip.x264.mkv -ovc xvid -xvidencopts bitrate=800:pass=2 -oac copy -o Immortals.2011.720p.BRRip.xviD.avi

This one gave more results about an unsupported pixel format with the audio
Both gave moments of the same frames..

    $ mencoder Immortals.2011.720p.BRRip.x264.mkv -ovc xvid -xvidencopts bitrate=800:pass=2 -oac mp3lame -lameopts vbr=1 -o Immortals.2011.720p.BRRip.xviD.avi

both gave the following:

> MP3 audio selected. Unsupported PixelFormat 61 Unsupported PixelFormat
> 53 Unsupported PixelFormat 81
>
> This one specifically gave this:
>

    $ mencoder Immortals.2011.720p.BRRip.x264.mkv -ovc xvid -xvidencopts
    bitrate=800:pass=2 -oac mp3lame -lameopts vbr=1 -o
    Immortals.2011.720p.BRRip.xviD.avi

>
> success: format: 0 data: 0x0 - 0x7a1b4576 libavformat version 53.21.0
> (external) Mismatching header version 53.19.0 libavformat file format
> detected. [matroska,webm @ 0xb6aced80]max_analyze_duration reached
> [matroska,webm @ 0xb6aced80]Estimating duration from bitrate, this may
> be inaccurate [lavf] stream 0: video (h264), -vid 0 [lavf] stream 1:
> audio (ac3), -aid 0, -alang eng [lavf] stream 2: subtitle (text), -sid
> 0, -slang eng VIDEO: [H264] 1280x690 0bpp 23.976 fps 0.0 kbps (
> 0.0 kbyte/s) [V] filefmt:44 fourcc:0x34363248 size:1280x690 fps:23.976 ftime:=0.0417
> ========================================================================== Opening audio decoder: [ffmpeg] FFmpeg/libavcodec audio decoders
> libavcodec version 53.35.0 (external) Mismatching header version
> 53.32.2 AUDIO: 48000 Hz, 2 ch, s16le, 448.0 kbit/29.17% (ratio: 56000->192000) Selected audio codec: [ffac3] afm: ffmpeg (FFmpeg AC-3)
> ========================================================================== xvid: using library version 1.3.2 (build xvid-1.3.2) Opening video
> filter: [expand osd=1] Expand: -1 x -1, -1 ; -1, osd: 1, aspect:
> 0.000000, round: 1
> ========================================================================== Opening video decoder: [ffmpeg] FFmpeg's libavcodec codec family
> Selected video codec: [ffh264] vfm: ffmpeg (FFmpeg H.264)
> ========================================================================== MP3 audio selected. Unsupported PixelFormat 61 Unsupported PixelFormat
> 53 Unsupported PixelFormat 81 Pos: 0.0s 2f ( 0%) 0.00fps Trem:
> 0min 0mb A-V:0.004 [0:0] Movie-Aspect is 1.86:1 - prescaling to
> correct movie aspect. videocodec: XviD (1280x690 fourcc=44495658
> [XVID]) xvid: par=0/0 (vga11), displayed=1280x690, sampled=1280x690
> xvid: 2Pass Rate Control -- 2nd pass -- bitrate=800kbit/s Writing
> header... ODML: vprp aspect is 16384:8831. Setting audio delay to
> 0.048s. Writing header... ODML: vprp aspect is 16384:8831. Setting audio delay to 0.048s.
>
> 1 duplicate frame(s)! Pos: 1.2s 29f ( 0%) 0.00fps Trem: 9min
> 47mb A-V:0.084 [98:169]]
>
> Skipping frame! Pos: 1.9s 48f ( 0%) 13.11fps Trem: 56min 285mb
> A-V:0.051 [1081:192Pos: 2.0s 49f ( 0%) 12.24fps Trem: 61min
> 310mb A-V:0.055 [1170:193Pos: 2.0s 50f ( 0%) 12.10fps Trem:
> 63min 323mb A-V:0.051 [1201:195

Then I stopped the command