Inotify is a Linux kernel framework that notifies userspace applications of filesystem events. The iprocess program subscribes to inotify events on directories and executes commands when events are received. For example, iprocess can be used to automatically compress and move MP3 files when they are added to a watched directory. Id3v2 is a standard for embedding metadata like album art in MP3 files. The id3image program can extract or embed album art images in MP3 files. Together these tools allow automating workflows like compressing songs for a mobile phone with limited storage when the songs are downloaded.

1. inotify
Inotify is a framework inside Linux kernel which will notify filesystem
events to subscribed userspace applications.
We will explore briefly about how we can use these notifications to
automate workflows in a production system (or in a home system)
By Mohan R
Session at ILUGC meet on 2012.08.11

2. programming with inotify
● #include <sys/inotify.h>
●inotify_init() to get file descriptor (in other terms, a pipeline from
kernel).
●inotify_add_watch() to get watch file descriptor for each directory
you want to listen for events.
● inotify_rm_watch() to remove directories from watching
● read() to get event data from kernel

3. iprocess
●A simple program which subscribes to inotify with set of directories
and then execute commands whenever it gets event data from
kernel.
● Capable of using your multi-core cpu with full advantage as it uses
threads.
● Source code lives at github.

4. Iprocess in action
$ iprocess -d /work/ftp_downloads -m IN_CREATE,IN_MODIFY
“gzip [fullname] && mv [fullname].gz
/work/ftp_downloads_gzipped” -n 2
This above command will listen for changes in /work/ftp_downloads
directory, if a new file arrives to that directory, it will be automatically
compressed using gzip and moved to another directory called
/work/ftp_downloads_gzipped.
Above command can compress 2 files at a time using 2 of
machine's cpu cores.

5. Use Case
Requirement: I have a mobile with limited memory (1GB). I want my
favourite songs but dont want to give up my memory only for mp3
songs because I surf through my opera when I get bored and
sometime I download interesting things if I come across.
As per today's standard, one 320kbps mp3 song file of a tamil movie
will come around 10MB. By average, one tamil movie contains 5
songs. So, If I want 2 tamil movie songs into my mobile, I need to give
up 100MB.
There is a way to reduce size of mp3 files by reducing it's bitrate to
128kbps trading off it's quality for size. So, If I reduce 10MB file to
5MB, then I need to give up only 50MB.
is the killer for these kind of compression/conversion tasks. Some
bureaucracy happened and nowadays, major distros pack libav instead
of ffmpeg.

6. Contd..
I wrote a script called mobilecompress.sh which will take a mp3
song's filename, reduce its bitrate and produces an output with
given output filename. It uses avconv(ffmpeg) to reduce the bitrate.
Combining the power of iprocess with mobilecompress.sh, I'm
going to automate compression flow, Lets go to the command line,
$ iprocess -d /home/mohan/Music/ToConvert -m
IN_CREATE,IN_MODIFY
“/home/mohan/Development/scripts/mobilecompress.sh
[fullname] /home/mohan/Music/Converted/[name]”
Above command will convert any file arrives at ToConvert directory
and produces output in Converted directory
All I need to do is, download the mp3 files from Internet and put it
inside ToConvert directory, iprocess+mobilecompress.sh will take
care of reducing its size for my mobile.

7. Id3v2 and id3image
● Id3v2 is a standard to embed additional information to mp3 files
like composer, album, singers etc.,
●We can also embed Album posters directly into mp3 files. Music
players capable of reading id3v2 information can display that poster
whenever it plays that mp3 file.
●Id3lib is a open source c++ library which can operate on id3v2
data.
●Id3image is a program which can extract the poster image from
mp3 file or can embed new image into the mp3 file.
● Source is currently lives inside github.

8. Id3v2 and id3image
$ id3image -i /home/mohan/Downloads/AvanIvan.jpg
/home/mohan/Music/YuvanHits/AvanIvan/DiaDiaDole.mp3
Above command will extract AvanIvan.jpg file from
DiaDiaDole.mp3.
$ id3image -l -i /home/mohan/Downloads/Billa2.jpg
/home/mohan/Music/Converted/Billa2/*
Above command will embed Billa2.img into all the files inside
Converted/Billa2 directory.

9. Finally..
Lets play the songs..

10. Question Time
Any Question???