$(for n in $(seq 0 5 100); do
printf '<button class="%s" type="submit" name="vol" value="%s"> </button>' "$([ "$volume" = "$n" ] && printf selected)" "$n"
done)
+ <br>
+ <button type="submit" name="osd" value="progression">Progress</button>
</form>
<span class="info length">$(($length / 60)):$(($length % 60)) min</span>