Ubuntu does not distribute proprietary codes. First thing you need to do is to rebuild ffmpeg.  Since Ubuntu 8.04 Hardy Heron ships with ffmpeg from 2007, which is aeons old in video codec years, you need to build libx264 and ffmpeg from SVN sources. Here are detailed, valid, instructions. Note that FFMPEG trunk is not currently stable (September 2008), so you need to use revision 15261 which needs this little patch. Indeed, this is a very difficult month to start your career in the dark world of video encoders.

To make it legal and support open source codec development,  please pay for your codecs.

Then we use this guide by Robert Swain. We have a tiny sub 2,4″ screen, we do not care about the quality and do one pass encoding. By empirical research, I have found that the following MPEG-4 profile parameters are compatible with N95 8 GB and provide the optimal result. You can vary video and audio bitrate depending on your taste.

Here is a script which recursivelu encodes all detected video files suitable for mobile format:

#!/bin/sh
#
# Optimal movie encoding for Nokia N-series mobile phones
#
# Copyright 2008 Red Innovation Ltd.
#
# Say hi if you find this useful.
# We do some professional mobile video publishing, so if you
# need a helping hand please call us.
#
# Usage: Run encode.sh in any folder and all video files are recursively converted to mobile phone suitable format
#
# Note: We expect all the source material be in 16:9 aspect ration
#
# Also see http://www.nseries.com/index.html#l=support,search,faq,general,video%20encoding,53848
#

VIDEO_BITRATE=300k

AUDIO_BITRATE=72k

# Assume locally build ffmpeg + x264 in /usr/local/bin
# http://ubuntuforums.org/showthread.php?t=786095
export LD_LIBRARY_PATH=/usr/local/lib

# Search all source AVI, MPG and WMV video files
# Place all encoded files to the same folder with the source, with added .mp4 extension
find . -iname "*.avi" -or -iname "*.wmv" -or -iname "*.mpg" | while read src ; do
        srcfile=`basename "$src"`
	srcfolder=`dirname "$src"`
	dstfile="$srcfolder"/"$srcfile".mp4

	# The magical string!
	# Size and cropping is for 16:9 source material, so that 320:240 display will have black bars.
	# Fex pixels off... note that h264 sizes must be multiplies of 16, use 256x144 for streaming
	# N95 RealMedia player does not seem to respect MPEG-4 embedded aspect ration info.
	/usr/local/bin/ffmpeg -y -i "$srcfile" -acodec libfaac -ab $AUDIO_BITRATE -s 320x176 -aspect 16:9 -vcodec libx264 -b $VIDEO_BITRATE -qcomp 0.6 -qmin 16 -qmax 51 -qdiff 4 -flags +loop -cmp +chroma -subq 7 -refs 6 -g 250 -keyint_min 25 -rc_eq 'blurCplx^(1-qComp)' -sc_threshold 40 -me_range 12 -i_qfactor 0.71 -directpred 3 "$dstfile"

done