Re: [Mpg123-users] Decoding small clip of mpeg audio

[Thomas O. <tho...@or...>]

Am Sun, 29 Jun 2008 23:22:05 +0100
schrieb Nicholas J Humfrey <nj...@ec...>: 

> Has anyone tried using mpg123 to decode small sections of a large MP3  
> to Wave file?

I'd bet on it;-)

> I have some MPEG Audio files, that I want to extract 30 second clips  
> from. It would be nice if I could give mpg123 the time ranges that I  
> want to extract.

In a way, you can.

> I guess with CBR files, I could do it using frame  
> counting, but it would be nice to just pass the times directly to  
> mpg123.

Oh, that has nothing to do with CBR. A file can as VBR as it likes, the time per frame (number of samples) is fixed, as long as the file doesn't vary between MPEG versions/layers.
So for a off-the-street mp3 you can calculate

	time = frames * 1152 / samplingrate

> Before I start looking at hacking support into mpg123

There is not much hacking needed... the control interface already knows a command to seek to a specific position in seconds.
The libmpg123 API actually has a seek function using samples.
We just need to settle on the names for the new command line parameters;-)

Suggestions?


>         -k num, --skip num
>         -n num, --frames num

Right, you can already use that to get 10 frames from the 100th frame on... the inconveniency is to have some knowledge about what a frame means.


Alrighty then,

Thomas (who is reworking httpget.c with the added goal of IPv6 at the moment).