Re: [Alsa-user] Recording raw audio, and encoding it later

[John H. <jc...@th...>]

On 14 Sep 2010, at 03:10, Sam Varshavchik wrote:

> I would like to capture raw audio, chew on it with my own code, then save the result into some common format, such as wav or mp3. I'm trying to understand the description of sample formats given in the arecord man page:
> 
>      -f --format=FORMAT
>             Sample format
>             Recognized sample formats are: S8 U8 S16_LE S16_BE U16_LE U16_BE
> 
> So, if I understand the man page correctly, then if I run "arecord -t raw -c 1 -f U16_LE -r 8000", then the resulting file will have, basically, raw 16 bit samples, mono, 8000 samples per second, is this correct?
> 

I believe so.   However, you're probably better off sticking with WAV format files.   The only difference between a wav file and a raw file with the same recording parameters is a 44 byte header.   It is possibly to produce wav files that are more complicated, and I'm sure they exist, but I've never seen one.

If you can't find that spec for the 44 byte header, let me know (off list) and I'll send you the sample program I wrote a while back.

The main reason that there's an advantage is that in order to insert the 44 byte header, you have to copy the entire audio file.   If it's short that's not an issue, but if it's long ....  The second reason is that you don't have to remember that you changed the recording parameters, they're recorded in the header.

jch