Mp3 Aggregation with EWA

Author:	Jacob Smullyan
Date:	2007-02-08

Introduction to East-West Audio, an mp3-splicing system.

Promos: A Podcaster's Pickle

Podcasters want to lard their podcasts with not-so-evergreen promotional material (intros, ads, outros) which should periodically be rotated.

Remastering scales poorly; it is slow and CPU-intensive, and requires that lossless masters be available.

If remastered files need to be uploaded to a web server, every changed file needs to be transferred, even if only one promo has changed -- a big waste of bandwidth.

EWA: A Solution to Promo Rotation

• Builds the composite mp3s on the fly on the web server.
• Add any number of promos before and/or after the main content file.
• The content file's ID3 tags are copied to the composite file.
• Splicing just works: no bad frames at splice points.
• Fast: little performance difference from serving static files in typical use.
• Featureful, extensible rule system for determining what files get aggregated for a particular request.
• EWA is free software released under the Gnu Public License.

Limitations

• MP3s only (and currently only CBR).
• Only one content file per composite file.
• Not intended to do personalization.

Requirements

• A modern UNIX (Linux, *BSD, OS X) operating system -- Windows currently not supported.
• Ewa caches the composite files on disk, so requires (in the worst case) roughly twice the amount of disk space requires for the mp3 masters alone. (In practice, you can use much less cache space.)
• a web server that supports X-Sendfile: lighttpd or Apache with mod_xsendfile.
• Python 2.4 or better.
• Some Python dependencies: eyeD3, flup, ply.
• LAME

Rule Configuration Example

02/08/2007 - 02/17/2007: [

  and(< 02-06-2007 [F, fmt=MMDDYY],
      regex:"^(radiolab|otm)/\1\d{6}"):
    pre: [pledge.wav]
    post: []

  default
]

regex:"^(radiolab|otm)/\1\d{6}":
  pre: ["${1}_intro.wav", ad.wav],
  post: ["${1}_outro.wav"]

default

More Information

• Website: http://eastwestaudio.wnyc.org/
• the EWA Manual
• ewa-discuss Google Group