[SOLVED] Bash script to build up a command

GPGAgent · 07-02-2020, 05:29 PM

I know how to use getopts to get input to my bash script, and I know how to write a loop.

What I want to do is to prompt for a start and end points to cut from a video file, and then to build up an ffmpeg command to process the file (I know how to do that).

So it will prompt for

file name - just once - no problem here
then it should prompt for

Start

End

repeat this till it gets an E for Execute

Then I know how to write loop using a count on the number of start /end pairs read.

Quedtion how do I store the start/end pairs, in an array or a list, or some other way?

I'm just looking for some tips please.

michaelk · 07-02-2020, 06:02 PM

Basically what ever is easiest for you. Can you build up the command as you prompt for start/end? Then if necessary just concatenate the strings together.

If so then the added complexity of using an array is not required.

rtmistler · 07-02-2020, 06:42 PM

The best suggestion, since you know how to do nearly all of it, is to start writing a script and post it.

See my blog, in my signature for tips.

GPGAgent · 07-03-2020, 03:12 AM

Cheers all

ondoho · 07-03-2020, 04:39 AM

That is a script I would love to use myself!
Have you written it yet? Can you share it?

GPGAgent · 07-03-2020, 06:37 AM

Quote:

Originally Posted by ondoho

That is a script I would love to use myself!
Have you written it yet? Can you share it?

In progress - and yes I will share it

GPGAgent · 07-03-2020, 10:31 AM

Quote:

Originally Posted by ondoho

That is a script I would love to use myself!
Have you written it yet? Can you share it?

Here it is, a bit crude, but it works

Code:

#!/bin/bash
finished=false
while ! $finished; do
read -e -p "Movie To cut up: " FN
if [ ! -f "$FN" ]; then
    echo "File not found - try again"
    echo "=========================="
else
    finished=true
fi
done

echo "Now get on with the script"
unset T1
unset T2
finished=false
COUNT=0
while ! $finished; do
read -p "start cut - (0 to finish): " START
if [ "$START" -eq "0"  ]; then 
    break 
fi

read -p "end cut: "   END
((COUNT++))     ## iNCREMENT A COUNTER
echo $COUNT $START $END 
T1+="[0:v]trim=start=$START:end=$END,setpts=PTS-STARTPTS[pv$COUNT];[0:a]atrim=start=$START:end=$END,asetpts=PTS-STARTPTS[pa$COUNT];"
T2+="[pv$COUNT][pa$COUNT]"
done
echo "Now get on with the script again"
T2+="concat=n=$COUNT:v=1:a=1[VV][AA]"
echo $T1$T2
echo "/usr/bin/ffmpeg -y -i "$FN" -filter_complex "$T1""$T2" -map \"[VV]\" -map \"[AA]\" outx.mp4" > CutOutBits.txt
 /usr/bin/ffmpeg -y -i "$FN" -filter_complex "$T1""$T2" -map "[VV]" -map "[AA]" outx.mp4

I just need to prompt for an output filename

GPGAgent · 07-03-2020, 11:10 AM

I should add that the script does not do any validation other than the existance of the input file. It should check the start point is less than the end point, it should check it's not overwriting a file on output, and maybe it should let you input the start and end points in hh:mm:ss.s format, at the moment it expects seconds - I think.

ondoho · 07-04-2020, 03:40 AM

On modern ffmpeg versions I think one should use the '-ss' and '-t' options, along with '-c:a copy -c:v copy' to avoid re-encoding.

GPGAgent · 07-04-2020, 05:21 AM

Quote:

Originally Posted by ondoho

On modern ffmpeg versions I think one should use the '-ss' and '-t' options, along with '-c:a copy -c:v copy' to avoid re-encoding.

I do that when I just want one clip, I'll try it doing multiple clips. And yes I know I could clip the pieces I want to keep in a nuber if ffmpeg runs and then joining them with another ffmpeg command, followed by deleting the clips.

I really want to do this with a single ffmpeg command.

And in some instances my input file is a .mts file (video recorded on a cheap chinese set top box) and I do want to re-encoe it to .mp4.

Cheers

ondoho · 07-04-2020, 05:30 AM

Quote:

Originally Posted by GPGAgent

I really want to do this with a single ffmpeg command.

I understand.
But avoiding re-encoding is the more important thing here IMO. Snipping together bits from one video file should not require that.
I do not know whether your command does that or not; I suspect your "filter_complex" option does re-encode. Quick test: How long does it take (on a fairly recent consumer device), for a few minutes of video?

GPGAgent · 07-04-2020, 06:10 AM

Quote:

Originally Posted by ondoho

I understand.
But avoiding re-encoding is the more important thing here IMO. Snipping together bits from one video file should not require that.
I do not know whether your command does that or not; I suspect your "filter_complex" option does re-encode. Quick test: How long does it take (on a fairly recent consumer device), for a few minutes of video?

I need to re-encode from .mts to .mp4, and yes it does in fact re-encode

I'll do a test of .mp4 to .mp4 and report back - cheers

pan64 · 07-04-2020, 09:01 AM

I would try to use array[s] when I construct a command like this.
www.shellcheck.net will give you some additional hints.

GPGAgent · 07-04-2020, 09:55 AM

Quote:

Originally Posted by pan64

I would try to use array[s] when I construct a command like this.
www.shellcheck.net will give you some additional hints.

Cheers pan64, but using a variable is working just fine.

GPGAgent · 07-04-2020, 10:18 AM

My cutting script is working just fine, but for one final tweak, always the case innit!

I've added -s WxH so I can change the output size to suit where I'm going to be playing the video. I hold this in a variable called SIZE

This is the relevant bit of the bash script with the variable SIZE

Code:

SIZE="-s 512x288"
echo SIZE: $SIZE
echo "/usr/bin/ffmpeg -y -i ${FN} -filter_complex \"${T1}\"${T2} -map \"[VV]\" -map \"[AA]\" $SIZE ${OFN}" > CutOutBits.txt
/usr/bin/ffmpeg -y -i "${FN}" -filter_complex "${T1}""${T2}" -map "[VV]" -map "[AA]"  $SIZE "${OFN}"
exit

This is the problem - the - gets dropped from -s 512x288 on the ffmpeg command but you can see it's there when I echo it before executing the ffmpeg command
Terminal output:

Code:

charlie@charlie-machine:~/000TEST/Cutting$ ./CutOutBits.sh 
Movie To cut up: beach.mp4 
Output filename example.mp4: rtyu.mp4
start cut (h:mm:ss) - (e to finish) : 0:0:10
end cut (h:mm:ss): 0:0:50
1 10 50
start cut (h:mm:ss) - (e to finish) : e
Now get on with the script again
SIZE: -s 512x288
      ==========
    ffmpeg messages follow and removed
Unrecognized option 's 512x288'.
Error splitting the argument list: Option not found
charlie@charlie-machine:~/000TEST/Cutting$

And you can see in the script I save the command to a file which is this and you can see $SIZE has been expanded correctly i.e. -s 512x288

Code:

/usr/bin/ffmpeg -y -i beach.mp4 -filter_complex "[0:v]trim=start=10:end=50,setpts=PTS-STARTPTS[pv1];[0:a]atrim=start=10:end=50,asetpts=PTS-STARTPTS[pa1];"[pv1][pa1]concat=n=1:v=1:a=1[VV][AA] -map "[VV]" -map "[AA]" -s 512x288 rtyu.mp4

I can paste the above code into a terminal and works just fine, no reason why it shouldn't.
Whats causing the SIZE variable to expand incorrectly? How can i preserve the minus sign?

Breaking news - a workround - of sorts

I removed the -s from the variable so SIZE only has WxH, and the -s is in command line now -s $SIZE

Code:

SIZE="448x252"
/usr/bin/ffmpeg -y -i "${FN}" -filter_complex "${T1}""${T2}" -map "[VV]" -map "[AA]" -s $SIZE "${OFN}"
                                                                                     =========
exit