[Vorbis-dev] How to get the actual bitrate?

[Silvia Pfeiffer]

On Tue, Jan 26, 2010 at 2:17 PM, Lucas Clemente Vella <lvella at gmail.com> wrote:
> 揭磊平 escreveu:
>> Dear all:
>>   I'm a developer in china, and i really want to know how to calculate a ogg audio file's bitrate and then i can get the duration by file size.
>>   thanks very much for your answer.
>
> See, most of ogg vorbis files have variable bitrate, so the way to
> calculate its mean bitrate -- the only significant bitrate when speaking
> of the whole stream -- is size/duration, what imply you must know the
> duration beforehand.
>
> I'm afraid you can't know the duration of the stream by just looking at
> the file size, since even libvorbis must be able to seek through the
> stream to be able to determine it's duration.

You can seek to the last page, decode the granulepos and calculate the
duration from that.

Cheers,
Silvia.