Split ogg vorbis stream without BOS

Question

Input: a stream of ogg/vorbis coming from an encoder chip of an embedded system.

Problem: create output chunks of one second without transcoding.

Issue: the stream is being read "in the middle", so the first page with BOS (Beginning of Stream) is not available. Since the encoder chip has always the same parameters, I'd like to recreate the BOS page using the BOS page of a stream that was read from the start (reference stream).

I am trying to use vcut. I modified it so that it creates infinite chunks of one second. It was easy, and it works with files and streams with BOS. I also hacked it so that I wrote to a file the first pages of the reference stream and then read them before reading the production stream with no BOS. In this way, vs->headers are populated. When I detect a page serial number change, I change it so that vcut and libogg do not freak:

int process_page(vcut_state *s, ogg_page *page) {
    ...
    else if(vs->serial != ogg_page_serialno(page))
    {
        // fprintf(stderr, _("Multiplexed bitstreams are not supported.\n"));

        vs->stream_in.serialno = ogg_page_serialno(page);
        vs->serial = ogg_page_serialno(page);
        vs->granulepos = -1;
        vs->initial_granpos = 0;
        // ogg_stream_init(&vs->stream_in, vs->serial);
        // vorbis_info_init(&vs->vi);
        // vorbis_comment_init(&vs->vc);
        s->vorbis_init = 1;
    }

However, this gigantic hack does not work. How to solve this issue?

Answer 1

It actually works: see VS1053 split ogg.

What I needed to do was to consider that starting reading in the middle of the stream, granulepos was naturally high. So it was mine logical mistake.

In process_audio_packet, I added:

int process_audio_packet(vcut_state *s,
        vcut_vorbis_stream *vs, ogg_packet *packet)
{
    ...

    if(packet->granulepos >= 0)
    {

        if (!firstNonZeroGranule) { // my addition
            firstNonZeroGranule = 1;
            vs->initial_granpos = packet->granulepos - bs;
            if(vs->initial_granpos < 0)
                vs->initial_granpos = 0;
        } else if(vs->granulepos == 0 && packet->granulepos != bs) {
...