Re: Truncating an audio file

Subject: Re: Truncating an audio file
From: Kevin Dixon <email@hidden>
Date: Wed, 31 Jul 2013 22:17:03 -0700

AIFF and WAV should also work perfectly, as they are flat files (header, header, PCM), though you will have to close/truncate the file, the open and update the header to have correct info about duration, etc.
I think you will find you need to update the header of MP3 as well, though "missing data", if it falls after a frame boundary, will probably just generate a warning in a decoder--then again, 60 seconds of silence should compress pretty well-- you'll have to update the header regardless if you want the length info to be right.

-Kevin

On Wed, Jul 31, 2013 at 10:06 PM, Jens Alfke <email@hidden> wrote:

On Jul 31, 2013, at 12:34 PM, patrick machielse <email@hidden> wrote:

In an application, I'm recording audio to file using the ExtAudioFile API. After recording is finished, there may be the need to chop off up to 60 seconds of audio from the end of the file (which will be silence).

ExtAudioFile doesn't seem to have functions that would support this type of operation.

It’s been a long time since I looked at the API; if it has a way to get the byte offset corresponding to a particular timestamp, you can then just pass that offset to the truncate() system call.

Whether this will actually work correctly depends on the file format, though. It should work with MPEG-type formats like MP3 and AAC because the decoder just looks for frames in the file and doesn’t expect anything else around them. It might not work for AIFF though. Experiment :)

—Jens

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References:
	>Truncating an audio file (From: patrick machielse <email@hidden>)
	>Re: Truncating an audio file (From: Jens Alfke <email@hidden>)

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