Ignore that, mencoder wasn't installed - apt-get fixed that.

Im now getting further, the Mediaplayer on the 770 opens now, but an error is generated - unable to perform operation then quits.

Seems that the call is passed to mencoder as per the console output ;

Width needs trimming by 0.0833333333333333 from 240 x 128
Invoking mencoder /var/lib/mythtv/videos/TV/Benidorm/Benidorm_Series1_Episode1.avi -o /home/mythtv/.mediaserv/data/TV/Benidorm/Benidorm_Series1_Episode1.avi.avi -srate 44100 -channels 1 -oac mp3lame -lameopts vbr=0:br=32:mode=3 -af volnorm,channels=1 -ovc lavc -lavcopts vcodec=mpeg4:vbitrate=80 -vf-add crop=586:352 -vf-add scale=240:144 -ofps 12.5 -ffourcc DIVX -noidx -force-avi-aspect 1.66666666666667...
MEncoder 2:1.0~rc1-0ubuntu9.1 (C) 2000-2006 MPlayer Team
CPU: AMD Athlon(TM) XP 3000+ (Family: 6, Model: 10, Stepping: 0)
CPUflags: Type: 6 MMX: 1 MMX2: 1 3DNow: 1 3DNow2: 1 SSE: 1 SSE2: 0
Compiled with runtime CPU detection.
success: format: 0 data: 0x0 - 0xadb2000
AVI file format detected.
VIDEO: [XVID] 640x352 12bpp 25.000 fps 955.4 kbps (116.6 kbyte/s)
[V] filefmt:3 fourcc:0x44495658 size:640x352 fps:25.00 ftime:=0.0400
================================================== ========================
Opening audio decoder: [mp3lib] MPEG layer-2, layer-3
AUDIO: 48000 Hz, 2 ch, s16le, 128.0 kbit/8.33% (ratio: 16000->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
Opening video filter: [scale w=240 h=144]
Opening video filter: [crop w=586 h=352]
Crop: 586 x 352, -1 ; -1
================================================== ========================
Opening video decoder: [ffmpeg] FFmpeg's libavcodec codec family
Selected video codec: [ffodivx] vfm: ffmpeg (FFmpeg MPEG-4)
================================================== ========================
Forcing output FourCC to 58564944 [DIVX].
VDec: vo config request - 640 x 352 (preferred colorspace: Planar YV12)
VDec: using Planar YV12 as output csp (no 0)
Movie-Aspect is 1.82:1 - prescaling to correct movie aspect.
videocodec: libavcodec (240x144 fourcc=58564944 [DIVX])
Writing header...
ODML: vprp aspect is 16384:9830.
Writing header...
ODML: vprp aspect is 16384:9830.