[Discuss-gnuradio] Re: gr.wavfile_source

[Martin Braun]

On Wed, Dec 17, 2008 at 11:17:11AM +0100, Dimitrios Symeonidis wrote:
> Hi Martin, I am trying to read a stereo wav file converted from an mp3 
> using audacity on ubuntu, and I get the error
> "RuntimeError: is not a valid wav file"
>
> I looked at the code
> http://gnuradio.org/trac/browser/gnuradio/branches/releases/3.1/gnuradio-core/src/lib/io/gr_wavfile_source.cc?rev=7808
> and I can see that it comes from
>         if (!gri_wavheader_parse(d_fp,
>                                  d_sample_rate,
>                                  d_nchans,
>                                  d_bytes_per_sample,
>                                  d_first_sample_pos,
>                                  d_samples_per_chan))
>
> how do you propose i create the wav file from mp3 on linux, in order to 
> have a valid wavheader?

Hi Dimitrios and whoever it may interest on the GR list,

the gr_wav* blocks only accept WAV if:

- They are uncompressed (RIFF/WAV supports some kind of compression)
- Samples are saved as integers, 8 or 16 bit resolution
- They must have a valid header (i.e. begin with 'RIFF....WAVEfmt ')

The latter should not be a problem with any audio program, including
audacity. I know audacity uses a proprietary floating point format
internally, so possibly one of the first conditions was violated?

An easy way to convert an mp3 to a GR-compatible WAV file is to use sox:

$ sox infile.mp3 -2 outfile.wav

The -2 switch converts the output to 16-bit samples.

Hope this helps,
Martin


> thank you in advance for your help
>
> ps you might want to publish your answer to discuss-gnuradio for future 
> reference...


-- 
Dipl.-Ing. Martin Braun           Phone: +49-(0)721-608 3790
Institut fuer Nachrichtentechnik  Fax:   +49-(0)721-608 6071
Universitaet Karlsruhe (TH)       http://www.int.uni-karlsruhe.de/

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