From: Konrad Meyer <konrad@...>
Date: 2007-12-15T11:02:11+09:00
Subject: Re: Work with Audio Files

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Quoth John Joyce:
>=20
> On Dec 14, 2007, at 7:12 PM, Konrad Meyer wrote:
>=20
> > Quoth Petr Kout:
> >> Lloyd Linklater wrote:
> >>> Petr Kout wrote:
> >>>> Hi,
> >>>>
> >>>> I am new to Ruby on Rails and I consider converting my application
> >>>> written in Java into Ruby. The question is, however, is there =20
> >>>> any plugin
> >>>> or other way to handle MP3 and other audio files? I need to Ruby =20
> >>>> to be
> >>>> able to tell me how long the uploaded MP3 is and ideally, give =20
> >>>> me the
> >>>> possibility to cut the file on the server if it's too long. I =20
> >>>> looked all
> >>>> over Google, nothing found. Thank you very much for any advice.
> >>>
> >>> http://www.ruby-forum.com/topic/130804#new
> >>
> >> Hi,
> >>
> >> thank you for the link, but it's not what I was looking for. I do not
> >> need to play the mp3 file. I need to be able to analyze it on the
> >> backend; that is, to get its length in seconds, and possibly =20
> >> truncate it
> >> (not necessary). I was doing it in Java so far. If I can't do this on
> >> the backend, I can't switch to Ruby, which is what I would love to =20
> >> do.
> >>
> >> Thanks.
> >>
> >> Peter
> >
> > There is a great library out in the wild called "metadata" that you =20
> > can use to
> > get information about mp3s (as well as many other filetypes) that I =20
> > think is
> > available in gem form. You might take a look at that.
> >
> > If you want to truncate a constant bitrate mp3, AFAIK they are =20
> > structured such
> > that you *could* crudely lop off some bytes from the end (channels *
> > time_to_clip * bitrate bytes). If not, you'll need to use some sort of
> > external mp3 library. I don't know of any that exist with ruby =20
> > bindings. You
> > might look at LAME though I'm not sure how much that will do.
> >
> > HTH,
> > --=20
> > Konrad Meyer <konrad@tylerc.org> http://konrad.sobertillnoon.com/
> Remember, keyword there was CONSTANT bitrate, variable bitrate might =20
> give you more trouble doing that without more care.
> Be sure any meta data matches changes or some apps might complain =20
> about the audio file.

Well, no, mp3 is made such that it can be streamed over the internet. Apps=
=20
should behave nicely even if the stream ends before they expect it. Variabl=
e=20
bitrate will not work, of course. Better use a tool. (Note "crudely" in the=
=20
original email.)

Regards,
=2D-=20
Konrad Meyer <konrad@tylerc.org> http://konrad.sobertillnoon.com/

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