[SciPy-User] RIFF header vs Scipy for odd length payloads

[Warren Weckesser]

On Tue, Sep 1, 2015 at 5:58 PM, Joseph Codadeen <jdmc80 at hotmail.com> wrote:

> Hi,
>
> Sample file is 16 bits
>
> As for a sample, not with me no. But you may create one simply by taking
> any HFP sample and playing with the RIFF
>



What is an "HFP sample"?




> header. Make the payload length an odd number adjusting the data, add a
> pad byte and adjust only the file length to represent this now even
> numbered file length, i.e. 36 byte header offset + odd payload length + 1
> pad byte.
>
> I amend mine easily in notepad++ .
>
> Read in the file;
>     scipy.io.wavfile.read(filepath)
>
> and scipy should complain as numpy doesn't like odd length files.
>
> I will try to share a sample tomorrow but it is simply an audio tone being
> played.
>
> As for the link on github, that was my original posting.
>
> Thanks.
> Joseph
>
>
> ------------------------------
> Date: Tue, 1 Sep 2015 14:20:00 -0400
> From: warren.weckesser at gmail.com
> To: scipy-user at scipy.org
> Subject: Re: [SciPy-User] RIFF header vs Scipy for odd length payloads
>
>
>
>
> On Tue, Sep 1, 2015 at 10:23 AM, Joseph Codadeen <jdmc80 at hotmail.com>
> wrote:
>
> Hi,
>
> (tried posting this before with no luck, retrying)
>
> I am a scipy newbie.
>
> The RIFF specification states;
>
> http://www.kk.iij4u.or.jp/~kondo/wave/mpidata.txt (definitive guide?)
>
>      ckSize    A 32-bit unsigned value identifying the
>                size of ckData. This size value does not
>                include the size of the ckID or ckSize
>                fields or the pad byte at the end of
>                ckData.
>      ckData    Binary data of fixed or variable size. The
>                start of ckData is word-aligned with
>                respect to the start of the RIFF file. If
>                the chunk size is an odd number of bytes, a
>                pad byte with value zero is written after
>                ckData. Word aligning improves access speed
>                (for chunks resident in memory) and
>                maintains compatibility with EA IFF. The
>                ckSize value does not include the pad byte.
>
>      <WORD>    16-bit unsigned        unsigned int
>                quantity in Intel
>                format
>
> However, if I do this and read my HFP wav file via scipy,
> <pre>framerate, data = scipy.io.wavfile.read(filepath)</pre>
>
>  it complains with;
> <pre>string size must be a multiple of element size</pre>
>
> A bit more debugging added to my test code and numpy (multiarray/ctors.c)
> gives:
>
> Sample file is 16 bits, note that 24 bit samples do not work in scipy
> Got error type "ValueError"
> Analysis of the wav file encountered a problem: "slen: 48683, itemsize: 2
> - string size must be a multiple of element size"
>
> i.e. my payload length is odd, reflecting the actual payload as per the
> the spec. The length of the file reflects the additional pad byte.
>
> So for odd length payloads;
> * we have the spec saying do not add the pad byte to the payload length,
> but only to the file length,
> * scipy likes the payload length to be even.
> * If I add the pad byte to to the payload length and the file length,
> scipy is happy.
> * If I want to follow the spec then no one can load my files into scipy.
>
> Am I misunderstanding something?
>
> What is the correct thing to do in this case?
> * Follow the spec
> * Follow scipy
> * Fix scipy
>
> I believe it should be to fix scipy unless I am looking at the wrong spec.
> The spec came from
> http://www.digitalpreservation.gov/formats/fdd/fdd000001.shtml
>
> I have tried this on scipy version 0.16.0 on Ubuntu 14.04 LTS
>
> Thanks.
>
>
>
> Could you provide a link to a wav file that demonstrates the problem?
>
> How many bits per sample is your file?  (Sorry, the answer is not clear to
> me from your email.)  Scipy's wav reader does not support 24 bit files.
> If your file is 24 bit, you can try wavio, a small module I wrote
> specifically to read 24 bit wav files into a numpy array:
> https://github.com/WarrenWeckesser/wavio
>
>
> Warren
>
> P.S. For anyone reading this, there is also an issue on github:
> https://github.com/scipy/scipy/issues/5175
>
>
>
>
>
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