[Octave-bug-tracker] [bug #49927] audioread slow when extracting only part of a file

[Rik]

Update of bug #49927 (project octave):

                  Status:               Need Info => Confirmed              
                 Release:                   4.0.0 => dev                    
        Operating System:       Microsoft Windows => Any                    
                 Summary: wavread/audioread refuses to continue reading
wav-file => audioread slow when extracting only part of a file

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Follow-up Comment #12:

kbhit is a separate issue.  That was fixed in 4.0.1, another reason why it's
important to run a supported version of Octave.

I think you're right that the problem is the straightforward, but
memory-intensive, strategy in audioread.cc of reading in the WHOLE file and
then extracting just the relevant bit.

This is the ine that does it


  OCTAVE_LOCAL_BUFFER (float, data, info.frames * info.channels);


OCTAVE_LOCAL_BUFFER uses new or malloc underneath to try and get a contiguous
block of memory.  Even if you have a fair amount of memory, it could be rare
to have a 575MB contiguous chunk.

The API for libsndfile is at http://www.mega-nerd.com/libsndfile/api.html.  In
particular, it looks like the input parsing for the second input which
determines which samples to extract could be moved up earlier.  Then the
OCTAVE_LOCAL_BUFFER call could be sized to a smaller value, the file pointer
could be advanced using sf_seek(), and sf_read_float() could be called with
only the number of items to read.

Re-titling bug report to reflect the underlying issue.


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