Re: How to use this AudioFile info thing?
Re: How to use this AudioFile info thing?
- Subject: Re: How to use this AudioFile info thing?
- From: David Duncan <email@hidden>
- Date: Thu, 5 May 2005 14:54:57 -0400
On May 5, 2005, at 02:42 PM, Richard Dobson wrote:
That isn't what I asked. Your previous post implied that there are
file formats of which you can only determine the duration by
"parsing the entire file". This is never required for WAVE or AIFF,
or for any sane soundfile format, because the length in sample
frames can be directly got from the header (at the beginning of the
file, we hope!).
VBR MP3 would be a format that requires you to parse the entire file
to know the time. I don't know how Vorbis does it, but the Ogg
container might store such information (I haven't looked). There are
probably other formats out there that have this issue as well.
A file doesn't "fill out" anything; some software algorithm has to
do that (is this some as yet undocumented element of the elusive
CAF format?).
CAF seems to be fairly straight forward to me. AudioToolbox/CAFFile.h
seems to document the format fairly well IMHO. It idea basically
seems to be 64-bit AIFF.
I want to know what file formats (compressed? headerless?) have to
be parsed over their entirety to know the duration. So I know to
avoid them, basically!
Any VBR format that isn't in a sane container generally. CBR formats
don't have this problem, regardless of the container (or lack
thereof) they are in (since you can do datasize/bitrate). I only know
of VBR MP3 for certain, someone else might know others.
And in any case, the calculation TotalFrames/SampleRate will only
be accurate to some number of decimal places. What would cause it
to be more approximate than this?
Generally, if TotalFrames is not exactly known. The accuracy is only
as good as the estimate of TotalFrames. The sample rate has to
obviously be known.
--
Reality is what, when you stop believing in it, doesn't go away.
Failure is not an option. It is a privilege reserved for those who try.
David Duncan
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