[LAU] Input to aplay to make a file instead?

[John Murphy]

On Sun, 19 Apr 2020 01:48:34 +0200 Gerhard Zintel wrote:

> Hi again,
> 
> On 19/04/2020 00:39, Gerhard Zintel wrote:
> > On 18/04/2020 12:05, John Murphy wrote:  
> >> If I simply '>' the input, which was going to aplay, to a file, it's
> >> done in a flash. Unplayable, but the file contains data. Could I write
> >> a header first somehow? Or a container format would be OK.  
> >
> > there are for sure "correct" ways to do it. If you want to use pure bash magic here you are:
> > Header of a wave file contains 44 byte. To extract it to a file use:
> >
> > head -c 44 original.wav > header.bin
> >
> > Now you can use your file from above (let's call it part.raw) and use:
> >
> > cat header.bin part.raw > newname.wav
> >
> > You should be able to play the new file. Be aware that the header is correct
> > except for the length information. You might fix this with
> > wavfix (https://github.com/agfline/wavfix). Furthermore if your parts are
> > not cut at a sample boundary (e.g. a normal wav file is stereo 16
> > bit per channel thus 4 byte per sample) you will get noise.  
> 
> One further remark. The wave header has two length information at byte offset 5 and 41
> (see http://www.topherlee.com/software/pcm-tut-wavformat.html). You can use dd like described
> here (https://unix.stackexchange.com/questions/214820/patching-a-binary-with-dd) to patch
> the created file newname.wav afterwards to inject the correct length information.
> 
> The length information has to be in binary representation. You could use the method described here
> (https://stackoverflow.com/questions/9955020/how-to-write-integer-to-binary-file-using-bash)
> to get the 4 byte representation of file newname.wav
> 
> A lot of shell magic but it seems to work.
> 
Hi Gerhard,

I thought I might need to abort attempts in that direction, as I used
Audacity to export exactly 5 seconds of audio from one of my files and
then used the player program to output a region of that's entire length
to a new file.

First I noticed the new file is much bigger than the file from Audacity
export, but then I saw it's actually exactly (Audacity_file - 44) * 2
so there's still hope.

Thanks a million for all the help. I had a quick look at using Python
to make files from region information lines. It has a wave module
which has 'setpos' and 'tell' methods which work in frames, so I'll
get there one way or another.

-- 
John.