Added usage messages to the scripts.

video_audio_merge

@@ -10,5 +10,4 @@ then
 	printf "$usage"
 	exit 1
 fi
-set -x
 ffmpeg -i "$2" -i "$3" -c:v copy -c:a aac -strict experimental "$1"

video_concat

@@ -1,7 +1,12 @@
 #!/bin/bash
-#losslessly concatenate video files while keeping audio good
-# see https://trac.ffmpeg.org/wiki/Concatenate#protocol
-# USAGE: video_concat output.mp4 input1.mp4 ... inputN.mp4
+usage="losslessly concatenate video files while keeping audio good
+ see https://trac.ffmpeg.org/wiki/Concatenate#protocol
+ USAGE: video_concat output.mp4 input1.mp4 ... inputN.mp4"
+if [[ -z "$1" ]] || [[ -z "$2" ]]
+then
+    printf "$usage"
+    exit 1
+fi
 concmd="concat:"
 output="$1"
 shift

video_extract

@@ -1,11 +1,11 @@
 #!/bin/bash
-# Extract a portion of a video (works for pure audio too)
-# USAGE:
-#   video_extract output input start_time to end_time
-#   video_extract output input start_time for duration
-# start and end time is in the format
-# HH:MM::SS.frac
-# duration is the length of the clip
+usage="Extract a portion of a video (works for pure audio too)
+ USAGE:
+   video_extract output input start_time to end_time
+   video_extract output input start_time for duration
+ start and end time is in the format
+ HH:MM::SS.frac
+ duration is the length of the clip"
 
 case $4 in
     "to")
@@ -15,8 +15,8 @@ case $4 in
         flag=-t
         ;;
     *)
-        echo "Error Specify to or for"
-        exit
+        printf "$usage"
+        exit 1
         ;;
 esac
 

video_get_audio

@@ -1,5 +1,11 @@
 #!/bin/bash
+usage="Extract audio from a video file
+ USAGE: video_get_audio output input
+"
 
-# Extract audio from a video file
-# USAGE: video_get_audio output input
-ffmpeg -i "$2" -vn -ab 256 "$1"
+if [[ -z $2 ]]
+then
+    printf "$usage"
+    exit 1
+fi
+ffmpeg -i "$2" -vn -ab 256 "$1"

video_mute

@@ -1,4 +1,10 @@
 #!/bin/bash
-# Mute a video file
-# USAGE: video_mute output.mp4 input.mp4
-ffmpeg -i "$2" -an "$1"
+usage="Mute (i.e., remove all sound from) a video file
+ USAGE: video_mute output.mp4 input.mp4
+"
+if [[ -z "$2" ]]
+then
+    printf "$usage"
+    exit 1
+fi
+ffmpeg -i "$2" -an "$1"