A bash script with which you should be able to import MTS files to Ubuntu/Debian from AVCHD camcoders.

mts.sh

#!/bin/bash

MTS_LIST=`mktemp /tmp/mts.XXXXXX`

THREADS_TOTAL=(`cat /proc/cpuinfo | egrep '^processor' | awk '{print $3}'`)

SPANNED_FILE_SIZE=4288180224 #This number varies by camera. This value is optimized for Panasonic HDC-HS100.

function func_new_thread(){
    local tmp_list=`mktemp /tmp/list.XXXXXX` || exit 1
    local tmp_cat=`mktemp /tmp/cat.XXXXXX` || exit 1
    # Create FIFO to allow input from multiple MTS files at once
    local tmp_fifo=`mktemp /tmp/fifo.XXXXXX` || exit 1
        rm ${tmp_fifo}
        mkfifo ${tmp_fifo}
    local line
    local ffmpeg_instances=()
    cat ${MTS_LIST} | grep ${1} | awk '{print $2}' > ${tmp_list}
    # Build cat script as input to fifo
    echo -n "cat " > ${tmp_cat}
    cat ${tmp_list} | while read line; do
        echo "\"${line}\" \\" >> ${tmp_cat}
    done
    echo "> ${tmp_fifo} &" >> ${tmp_cat}
    chmod +x ${tmp_cat}
    ${tmp_cat}
    ffmpeg_instances=(`pidof ffmpeg`)
    while :; do
        if [ ${#ffmpeg_instances[@]} -lt 2 ]; then
            echo "Launching a job with ID:${1}."
            nice -n 19 ffmpeg -loglevel fatal -i "${tmp_fifo}" -vcodec copy -acodec copy -threads ${#THREADS_TOTAL[@]} ~/${1}.MTS
            rm ${tmp_list}
            rm ${tmp_cat}
            rm ${tmp_fifo}
            echo "Completed a job with ID:${1}."
            break
        else
            sleep 1
            ffmpeg_instances=(`pidof ffmpeg`)
        fi
    done
}

if [ "`which ffmpeg`" == "" ]; then
    echo -e "This script requires \"ffmpeg\" installed. "
    exit 1
fi

# Detect USB storage
ARR_USB_STORAGE=(`dmesg | grep "Attached SCSI removable disk" | awk '{print $5}' | egrep '^\[' | sort | uniq | sed -e 's/\[//g' -e 's/\]//g'`)
if [ ${#ARR_USB_STORAGE[@]} -eq 0 ]; then
    exit 1
else
    # Detect USB storage that are actually mounted
    ARR_USB_STORAGE_MOUNTED=(`for ((COUNT = 0; COUNT < ${#ARR_USB_STORAGE[@]}; COUNT++)); do mount | grep ${ARR_USB_STORAGE[${COUNT}]}; done | awk '{print $3}'`)
    if [ ${#ARR_USB_STORAGE_MOUNTED[@]} -eq 0 ]; then
        echo "Detected no USB mass storage (mounted)."
        exit 1
    else
        for ((COUNT = 0; COUNT < ${#ARR_USB_STORAGE_MOUNTED[@]}; COUNT++)); do
            echo "Detected a USB mass storage (mounted) at ${ARR_USB_STORAGE_MOUNTED[${COUNT}]}."
            # Detect locations of MTS files within the mounted USB storage
            ARR_MTS_LOCATION=("${ARR_MTS_LOCATION[@]}" `find ${ARR_USB_STORAGE_MOUNTED[${COUNT}]} -type f | egrep '\.MTS$|\.mts$' | while read LINE; do dirname "${LINE}";done | uniq`)
        done
        # Detect file-spanning
        if [ ${#ARR_MTS_LOCATION[@]} -eq 0 ]; then
            exit 1
        else
            for ((COUNT = 0; COUNT < ${#ARR_MTS_LOCATION[@]}; COUNT++)); do
                echo "MTS files have been detected at ${ARR_MTS_LOCATION[${COUNT}]}."
            done
            CLIP_NUMBER="`date +"%Y%m%d%H%M"`00"
            for ((COUNT = 0; COUNT < ${#ARR_MTS_LOCATION[@]}; COUNT++)); do
                LANG=C;ls -l ${ARR_MTS_LOCATION[${COUNT}]} | egrep '^-' | egrep '\.MTS|\.mts' | awk '{print $9" "$5}' | while read LINE; do
                    FILE_NAME=`echo ${LINE} | awk '{print $1}'`
                    FILE_SIZE=`echo ${LINE} | awk '{print $2}'`
                    echo "${CLIP_NUMBER} ${ARR_MTS_LOCATION[${COUNT}]}/${FILE_NAME}" >> ${MTS_LIST}
                    if [ ${FILE_SIZE} -lt ${SPANNED_FILE_SIZE} ]; then
                        CLIP_NUMBER=`expr ${CLIP_NUMBER} + 1`
                    fi
                done
            done
            ARR_CLIP_ID=(`cat ${MTS_LIST} | awk '{print $1}' | sort | uniq`)
            if [ ${#ARR_CLIP_ID[@]} -eq 0 ]; then
                JOB_RUNNING=false
                exit 1
            else
                for ((COUNT = 0; COUNT < ${#ARR_CLIP_ID[@]}; COUNT++)); do
                    (func_new_thread ${ARR_CLIP_ID[${COUNT}]})&
                    JOB_RUNNING=true
                done
            fi
        fi
    fi
fi

while ${JOB_RUNNING}; do
    if [ "`find /tmp -maxdepth 1 -type f | egrep '\/list\.[a-z,A-Z,0-9]+$|\/cat\.[a-z,A-Z,0-9]+$|\/fifo\.[a-z,A-Z,0-9]+$'`" == "" ]; then
        JOB_RUNNING=false
    else
        sleep 5
    fi
done

rm ${MTS_LIST}