As part of the last post I initially used a bash script to generate the commands to output the individual videos. As per usual, when I finally got fed up of the limitations and syntax issues in bash I switched to a proper programming language, perl. However this time I learnt a neat trick to doing multi-line commands in bash with comments embedded using the array feature of bash. A multi-line command typically looks like:

        melt \
            color:black \
                out=$audiolen \
            ...

However what if you want to add comments into the command? You can’t.

To solve this create an array:

    cmd=(
        # Take black background track for same number of seconds as the MP3, then add 10 seconds of another image
        melt
            color:black
                out=$audiolen
        ...
    )

and then use the following magic to execute it:

"${cmd[@]}"

Using this you can also conditionally add in extra statements if you’re using a pipeline-type program such as imagemagick (convert) or melt:

    cmd+=(
        # Output to the file
        -consumer avformat
            target="$target"
            mlt_profile="hdv_720_25p"
            f=mpeg acodec=mp2 ab=96k vcodec=mpeg2video vb=1000k
    )