appending a string constant selectively within a while loop in bash - bash

Question

I have a script called automateutube that I edit in VIM and execute in the terminal with sh ./automateutube.sh This script pulls youtube links from a file called songs.txt and downloads the video from youtube then extracts the audio.
The songs.txt file looks like this
https://www.youtube.com/watch?v=IxQOlZ3pqtI
https://www.youtube.com/watch?v=IxQOlZ3pqtI
https://www.youtube.com/watch?v=IxQOlZ3pqtI
https://www.youtube.com/watch?v=IxQOlZ3pqtI
It is just a bunch of links, one per line.
The script looks like this
#!/bin/bash
while read p; do
x=/tmp/.youtube-dl-$(date +%y.%m.%d_%H.%M.%S)-$RANDOM.flv
youtube-dl --audio-quality 160k --output=$x --format=18 "$p"
ffmpeg -i $x -acodec libmp3lame -ac 2 -ab 128k -vn -y "$p"
rm $x
done <songs.txt
Now the first part executes. It downloads the video and starts to unpack it.
It is the second part that fails. ffmpeg -i $x -acodec libmp3lame -ac 2 -ab 128k -vn -y "$p"
This is because "$p" is supposed to be in format "filename.mp3" However as it is p takes the value of a youtube link, without ".mp3" appended.
This works for the first line
youtube-dl --audio-quality 160k --output=$x --format=18 "$p"
because "$p" is supposed to be in the form of a link there.
Now I have tried adding three lines in
a="$.mp3"
b="$p"
c=$b$a
and making ffmpeg -i $x -acodec libmp3lame -ac 2 -ab 128k -vn -y "$p"
into ffmpeg -i $x -acodec libmp3lame -ac 2 -ab 128k -vn -y "$c"
but I am still getting an error. Any ideas?
parse error, at least 3 arguments were expected, only 1 given in string 'om/watch?v=sOAHOxbMOJY'

Answer 1

So after some experimentation using advice from the comments, I came to this, which works.
#!/bin/sh
while read -r p; do
x=/tmp/.youtube-dl-$(date +%y.%m.%d_%H.%M.%S)-$RANDOM.flv
youtube-dl --audio-quality 160k --output="$x" --format=18 "$p"
SUBSTRING=$(echo "$p"| cut -c33-50)
ffmpeg -i "$x" -acodec libmp3lame -ac 2 -ab 128k -vn -y "$SUBSTRING.mp3" </dev/null
rm "$x"
done <songs.txt
What this fixes is keeping /'s out of the file name, and eliminating parser error.