Originally Posted by MadeInGermany

The classic approach is slow (run exiftool for each file) but safe:

Code:

total_folder_length=$(
  find . -maxdepth 1 \( -iname '*.mkv' -o -iname '*.mp4' -o -iname '*.avi' \) |
  while IFS= read -r fname 
  do
    exiftool -n -q -p '$Duration#' "$fname"
  done |
  awk '{sum+=$0} END {print sum+0}'
)

Originally Posted by RudiC

That is quite confusing a script. And, what does "get a bit borked" mean? Incorrect? Slow? Crashes?

A few comments:
- you don't need an echo "command substitution" for a variable assignment in general.
- the repeated varn=$(echo ... | awk ... ) could be replaced by a read var1 ... varn <<< ... in what seems to be your bash version (which you, alas, don't mention)
- don't run exiftool with an empty array if the result is crooked, test the array upfront.
- your presumed bash version offers extended pattern matching of pattern-lists when the extglob option is set, mayhap eliminating the need for the find command.
- your presumed bash version offers the %()T format specifier:

Code:

printf "%(%T)T\n" 78682
22:51:22