[opus] opus file trimming/clipping

[Matt Ruck]

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
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