Vorbis - Apr 2004 - Streaming ogg from filepointer pointing to archive of many oggs. Ogg stream does not stop after end of one ogg file - what to do ?

Hello,
I'm currently trying to implement streaming off ogg-files out of an archive
file using SDL and SDL_mixer for playback. Therefore i create a FILE *
filepointer, place it to the beginning of an ogg file inside the archive and
hand over the filepointer to ov_open. ( command: ov_open(fp, &music->vf,
NULL, 0) ). This works fine so far. The problem is: if i put many oggs
together in one archive, the playback stops only after the last ogg file.
Why is this a problem ? Suppose i want to play the ogg files in random
order. The playback must end after the current ogg, so the user can select a
random new ogg file, place the filepointer to it and play the ogg. 

So is there a method to determine when one ogg file ended and the other
begins ?

Current code looks like this:

/* Load an OGG stream from the given file pointer */
OGG_music *OGG_new(FILE *fp)
{
        OGG_music *music;int xx;

        music = (OGG_music *)malloc(sizeof *music);
        if ( music ) {
                /* Initialize the music structure */
                memset(music, 0, (sizeof *music));
                OGG_stop(music);
                OGG_setvolume(music, MIX_MAX_VOLUME);
                music->section = -1;

                if ( ov_open(fp, &music->vf, NULL, 0) < 0 ) {
                        SDL_SetError("Not an Ogg Vorbis audio
stream");
                        free(music);
                        return(NULL);
.....

<p>And playing the ogg:

/* Read some Ogg stream data and convert it for output */
static void OGG_getsome(OGG_music *music)
{
        int section;
        int len;
        char data[4096];
        SDL_AudioCVT *cvt;

        len = ov_read(&music->vf, data, sizeof(data), 0, 2, 1,
&section);
        if ( len <= 0 ) {
                if ( len == 0 ) {
                        music->playing = 0;
                }
                return;
        }
.....

<p><p>Any idea please ?

Thanks, andre

<p><p><p>_________________________________________
Andre Krause
Dipl. Inform.
Department of Biological Cybernetics
Faculty of Biology
University of Bielefeld
PO Box 10 01 31
33501 Bielefeld
Germany

Phone: +49-521-106-5519
Mobil: +49-177-7465055
Home : +49-521-3044776

Email: post@andre-krause.net

ICQ# : 68306404
More ways to contact me: http://wwp.icq.com/68306404

Homepage: http://www.andre-krause.net
http://www.andre-krause.de
_________________________________________
War isn't politics, my dear. It is indeed he only human activity that is
rottener than politics. RexStout
_________________________________________

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Hello,
I'm currently trying to implement streaming off ogg-files out of an archive
file using SDL and SDL_mixer for playback. Therefore i create a FILE *
filepointer, place it to the beginning of an ogg file inside the archive and
hand over the filepointer to ov_open. ( command: ov_open(fp, &music->vf,
NULL, 0) ). This works fine so far. The problem is: if i put many oggs
together in one archive, the playback stops only after the last ogg file.
Why is this a problem ? Suppose i want to play the ogg files in random
order. The playback must end after the current ogg, so the user can select a
random new ogg file, place the filepointer to it and play the ogg. 

So is there a method to determine when one ogg file ended and the other
begins ?

Current code looks like this:

/* Load an OGG stream from the given file pointer */ OGG_music *OGG_new(FILE
*fp) {
        OGG_music *music;int xx;

        music = (OGG_music *)malloc(sizeof *music);
        if ( music ) {
                /* Initialize the music structure */
                memset(music, 0, (sizeof *music));
                OGG_stop(music);
                OGG_setvolume(music, MIX_MAX_VOLUME);
                music->section = -1;

                if ( ov_open(fp, &music->vf, NULL, 0) < 0 ) {
                        SDL_SetError("Not an Ogg Vorbis audio
stream");
                        free(music);
                        return(NULL);
.....

<p>And playing the ogg:

/* Read some Ogg stream data and convert it for output */ static void
OGG_getsome(OGG_music *music) {
        int section;
        int len;
        char data[4096];
        SDL_AudioCVT *cvt;

        len = ov_read(&music->vf, data, sizeof(data), 0, 2, 1,
&section);
        if ( len <= 0 ) {
                if ( len == 0 ) {
                        music->playing = 0;
                }
                return;
        }
.....

<p><p>Any idea please ?

Thanks, andre

<p><p><p>_________________________________________
Andre Krause
Dipl. Inform.
Department of Biological Cybernetics
Faculty of Biology
University of Bielefeld
PO Box 10 01 31
33501 Bielefeld
Germany

Phone: +49-521-106-5519
Mobil: +49-177-7465055
Home : +49-521-3044776

Email: post@andre-krause.net

ICQ# : 68306404
More ways to contact me: http://wwp.icq.com/68306404

Homepage: http://www.andre-krause.net
http://www.andre-krause.de
_________________________________________
War isn't politics, my dear. It is indeed he only human activity that is
rottener than politics. RexStout _________________________________________

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Ogg project homepage: http://www.xiph.org/ogg/
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On Wed, Apr 21, 2004 at 09:01:31PM +0200, Andre Krause wrote:
> I'm currently trying to implement streaming off ogg-files out of an
archive
> file using SDL and SDL_mixer for playback. Therefore i create a FILE *
> filepointer, place it to the beginning of an ogg file inside the archive
and
> hand over the filepointer to ov_open. ( command: ov_open(fp,
&music->vf,
> NULL, 0) ). This works fine so far. The problem is: if i put many oggs
> together in one archive, the playback stops only after the last ogg file.
> Why is this a problem ? Suppose i want to play the ogg files in random
> order. The playback must end after the current ogg, so the user can select
a
> random new ogg file, place the filepointer to it and play the ogg.
The ogg vorbis libraries are written to 'do their best' when presented 
with corrupt data streams. Likely what's happening is that after 
reaching the end of the whatever segment you've started playback of, it 
just scans ahead and continues playing with the next valid ogg vorbis 
data it finds, and so on until EOF.
> So is there a method to determine when one ogg file ended and the other
> begins ?
This information is available from the vorbisfile internals (the ogg 
layer reports the gaps and segment changes). However, in an application 
where you've packed multiple independent files together in a wrapper, 
the best approach is probably to use the vorbisfile callback interface 
to just unwrap and hand it the data for the segment you want to play.

HTH,
 -r
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On Thursday 22 April 2004 05:01, Andre Krause wrote:
> Hello,
> I'm currently trying to implement streaming off ogg-files out of an
archive
> file using SDL and SDL_mixer for playback. Therefore i create a FILE *
> filepointer, place it to the beginning of an ogg file inside the archive
> and hand over the filepointer to ov_open. ( command: ov_open(fp,
> &music->vf, NULL, 0) ). This works fine so far. The problem is: if i
put
> many oggs together in one archive, the playback stops only after the last
> ogg file. Why is this a problem ? Suppose i want to play the ogg files in
> random order. The playback must end after the current ogg, so the user can
> select a random new ogg file, place the filepointer to it and play the ogg.
>
> So is there a method to determine when one ogg file ended and the other
> begins ?
>
There are two ways you can do this:

1) Check the 'section' variable after each call to ov_read(). If it has 
changed, then you've moved to a new ogg stream.

2) Use ov_open_callbacks() rather than ov_open(), and provide appropriate 
callbacks. The close callback can just do nothing (because you probably want 
to keep it open for playing some other file from the archive. The 
seek/tell/read callbacks should be simple wrappers, they just have to take 
into account the offset from the start of the archive that the individual 
file starts/ends. You'll want to return EOF appropriately from the read 
callback when you get to the end.

I'd recommend option 2.

Mike

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