Internet Radio to Podcast with Shell Tools

Once I had a script that did all I wanted it to do, I sent it in to LJ along with a first version of this article. LJ Editor in Chief Don Marti pointed out that I was missing one key component: my program was generating an RSS version 1.0 feed, but all the podcast-aware programs look for a version 2.0 feed—specifically for an XML tag named enclosure. Naturally, I assumed it would be a trivial change to my software, merely switching versions and adding the enclosure tag. I soon learned, however, that the XML::RSS Perl module can write RSS 2.0 but cannot read it. Several sleepless nights ensued, until I determined that Perl tools were available that could read RSS 2.0 but not write it. So, it was time to add some glue.

I started by adding two Perl modules to my system—you can install them (as root) with:

perl -e "install XML::RSS,XML::Simple" -MCPAN

You probably will be okay with answering any questions it asks with the default. If you haven't used the Comprehensive Perl Archive Network (CPAN) yet, it asks quite a few setup questions, such as choosing several mirror sites that are close to you. Otherwise, it simply asks about a dependency or two; say yes.

After the two modules and their required dependencies are installed, you need to create a new XML file with information about the show you want to capture. The great thing about XML is you can use any text editor to make a file that is readable by both humans and machines, making it easy to create, view, test and modify RSS feed files. Let's start with this skeleton, containing a basic title section:

<?xml version="1.0" encoding="UTF-8"?>

<rss version="2.0">

<channel>
<title>Hour of the Wolf</title>
<link>http://www.hourwolf.com</link>
<description>Science Fiction Talk Radio
  with Jim Freund</description>
<generator>WBAI Stream Capture
  using Linux shell tools</generator>
</channel>
</rss>

If you never have played with XML before, this is a good time to get your feet wet. A quick look at the file shows data items surrounded by HTML-like tags, where each <something> tag has a corresponding </something> to close the something section. This becomes more confusing later, though, when we add the alternate syntax, which looks like <tagname a=“A” b=“B” />.

Once I had gathered all the tools I needed, I added a few droplets of shell magic to arrive at this simple script:

#!/bin/bash
# catchthewolf - capture "Hour of the Wolf"

# For capturing the stream
DATE=`date +%F`  # Save the date as YYYY-MM-DD
YEAR=`date +%Y` # Save just the year as YYYY
FILE=/home/phil/wolf.$DATE.mp3 # Where to save it
STREAM=http://www.2600.com/wbai/wbai.m3u
DURATION=2.1h # enough to catch the show, plus a bit
#DURATION=30s # a quick run, just for testing

# For the RSS syndication
XML="/home/phil/wolfrss.xml" # file for the RSS feed
ITEMS=15  # Maximum items in RSS list
XTITLE="Hour of the Wolf - $DATE Broadcast"
XDATE=`date -R` # Date in RFC 822 format for RSS
i=\$i;o=\$o;m=\$m # replace "$" in the perl script

# For the id3v2 Tags
AUTHOR="Jim Freund"
ALBUM="WBAI Stream Rip"
TITLE="Hour of the Wolf - $DATE"

# Use mplayer to capture the stream
# at $STREAM to the file $FILE
/usr/local/bin/mplayer -really-quiet -cache 128 \
    -dumpfile $FILE -dumpaudio -playlist $STREAM &
# the & turns the capture into a background job

sleep $DURATION  # wait for the show to be over

kill $! # end the stream capture

# Tag the resulting captured .mp3
id3v2 -a "$AUTHOR" -A "$ALBUM" \
    -t "$TITLE" -y $YEAR -T 1/1 -g 255 \
    --TCON "Radio" $FILE

# Add a new entry in the rss file,
# keep the file to a max of $ITEMS entries,
# and change the file's date to right now.
/usr/bin/perl -e "use XML::RSS; use XML::Simple; \
    $i=XMLin('$XML');$o=$i;bless $o,XML::RSS; \
    $m=$i->{channel}{item};if((ref $m)ne ARRAY) \
    {$o->add_item(%$m);} else \
    {foreach $m (@{$m}) {$o->add_item(%$m);}} \
    $o->channel(lastBuildDate=>'$XDATE', \
    pubDate=>'$XDATE'); \
    $o->add_item(title=>'$XTITLE', \
    link=>$o->{'channel'}{'link'}, \
    pubDate=>'$XDATE', \
    enclosure=>{url=>'file://$FILE', \
    length=>(stat('$FILE'))[7], \
    type=>'audio/mpeg'}, mode=>'insert'); \
    pop(@{$o->{'items'}}) \
    while (@{$o->{'items'}}>$ITEMS); \
    $o->{encoding}='UTF-8'; $o->save('$XML');"

echo "Caught the wolf."

This doesn't look too simple, though. Let's dissect this script a bit to see how it all works. Notice the back-ticks (`) around the date commands. They take whatever is enclosed in the `` marks and run it as a command and then replace the entire `whatevercommand` with the output from that command. If I had needed the date only once, I could have written:

FILE=wolf.`/bin/date +%F`.mp3