opus - May 2013 - opus file trimming/clipping

Hello,

I am new to opus and C, so please forgive my basic question. I am trying to
trim a file to remove an extract at a specified starting and ending time --
an example would be to save an excerpt from a song as a ringtone. What is
the best way to accomplish this?


I have been trying to use op_pcm_seek, and the documentation for
op_pcm_seek says "Seek to the specified PCM offset, such that decoding will
begin at exactly the requested position."

Question: Is this the right approach and how do I then specify where the
decoding is supposed to stop?


I will describe the steps I've tried so far (maybe not the best approach):

I have tried modifying the opusfile-1.0.2/examples/seeking_example.c as a
base, replacing

            pcm_offset=(ogg_int64_t)(rand()/(double)RAND_MAX*pcm_length);

with

            pcm_offset=(ogg_int64_t)((double)pcm_length/2.0);

presumably to start the decoding at the middle of the file by:

             ret=op_pcm_seek(of,pcm_offset);

However, when I save the file using the
write_samples(buffer,nsamples,nchannels) function, the file is unreadable,
and the resulting file is less than half the size of the original file.

Thanks,
Matt
-------------- next part --------------
An HTML attachment was scrubbed...
URL:
http://lists.xiph.org/pipermail/opus/attachments/20130508/ac753dcf/attachment.htm

Matt Ruck wrote:
> I am new to opus and C, so please forgive my basic question. I am trying
> to trim a file to remove an extract at a specified starting and ending
> time -- an example would be to save an excerpt from a song as a
> ringtone. What is the best way to accomplish this?
Are you trying to produce a WAV file with the decoded output of just a 
segment of the input file, or are you trying to produce a new .opus file 
without re-encoding that segment?

I think producing a new .opus file would be ideal to maintain the benefits
of using the opus codec for transmission over the Internet, and I have had
success encoding to and decoding from .opus to .wav using opus-tools.

Thanks,
Matt


On Wed, May 8, 2013 at 8:41 PM, Timothy B. Terriberry <tterribe at
xiph.org>wrote:
> Matt Ruck wrote:
> > I am new to opus and C, so please forgive my basic question. I am
trying
> > to trim a file to remove an extract at a specified starting and ending
> > time -- an example would be to save an excerpt from a song as a
> > ringtone. What is the best way to accomplish this?
>
> Are you trying to produce a WAV file with the decoded output of just a
> segment of the input file, or are you trying to produce a new .opus file
> without re-encoding that segment?
>
> _______________________________________________
> opus mailing list
> opus at xiph.org
> http://lists.xiph.org/mailman/listinfo/opus
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL:
http://lists.xiph.org/pipermail/opus/attachments/20130508/e30ae885/attachment.htm