Mine

#!/bin/bash

# skeletal outline of proceedure to enable multi-processor support

max_procs=$(grep -cs ^processor /proc/cpuinfo)

mkfifo "$WORK_DIR/enc.fifo" 2>/dev/null
"${TOYUV_CMD[@]}" < "$WORK_DIR/enc.fifo" | "${IMGENC_CMD[@]}" 2>/dev/null  &

# make intermediary fifos for images.  They will get catted to enc.fifo
for ((n=1; n<=max_procs; n++)); do
    [[ ! -e "$WORK_DIR/temp-${n}.ppm" ]] && mkfifo "$WORK_DIR/temp-${n}.ppm"
done

unset num_procs
for ((frame=0; frame<endframe; frame++)); do
    ((num_procs++)) # how many processes are running
    out_ppm="$WORK_DIR/temp-${num_procs}.ppm" # current frame

    { command | command | command "$out_ppm" ; }

    impids="$impids $!"
        
    if ((num_procs==max_procs || frame == endframe-1)); then
        spin  "\rProcessing frame $(($frame + 1))  " >&2
        cat "${ppm_fifos[@]}"
        wait $impids
        unset num_procs ppm_fifos impids
    fi
done > "$WORK_DIR/enc.fifo"