核心參考 xiph官網(wǎng)

ogg 數(shù)據(jù)結構

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以上ogg中最大的結構為ogg流，對比ogg的存儲結構來說都是以ogg_page來進行數(shù)據(jù)分頁，但是對于用于來說是以ogg_packet來對數(shù)據(jù)進行裝載和解析。

編碼相關

概覽

When encoding, the encoding engine will output raw packets which must be placed into an Ogg bitstream. Raw packets are inserted into the stream, and an ogg_page is output when enough packets have been written to create a full page. The pages output are pointers to buffered packet segments, and can then be written out and saved as an ogg stream. There are a couple of basic steps: Use the encoding engine to produce a raw packet of data. Call ogg_stream_packetin to submit a raw packet to the stream. Use ogg_stream_pageout to output a page, if enough data has been submitted. Otherwise, continue submitting data.
意思就是原始數(shù)據(jù)要封裝在ogg_packet中通過ogg_stream_packetin方法寫入到ogg_stream_state中，如果包足夠通過ogg_stream_pageout方法將數(shù)據(jù)寫在ogg_page中

創(chuàng)建與銷毀

創(chuàng)建
ogg_stream_init(&stream_, 0 /* serial number */);
銷毀
ogg_stream_clear(&stream_);

編碼數(shù)據(jù)封裝

typedef struct {
  unsigned char *packet;//數(shù)據(jù)
  long  bytes;//數(shù)據(jù)大小
  long  b_o_s;//1代表開始包
  long  e_o_s;//1代表結束包
  //A number indicating the position of this packet in the decoded data. This is the last sample, frame or other unit of information ('granule') that can be completely decoded from this packet.
  ogg_int64_t  granulepos;
  ogg_int64_t  packetno;//Sequential number of this packet in the ogg bitstream.

} ogg_packet;

單流數(shù)據(jù)寫入

// Write the most recent buffer of Opus data into an Ogg packet.
  ogg_packet frame_packet;
  frame_packet.b_o_s = 0;
  frame_packet.e_o_s = flush ? 1 : 0;
  // According to
  // https://tools.ietf.org/html/draft-ietf-codec-oggopus-14#section-4 the
  // granule position should include all samples up to the last packet completed
  // on the page, so we need to update granule_position_ before assigning it to
  // the packet.  If we're closing the stream, we don't assume that the last
  // packet includes a full frame.
  if (flush) {
    granule_position_ += (elements_in_pcm_frame_ / num_channels_);
  } else {
    granule_position_ += frame_size_;
  }
  frame_packet.granulepos = granule_position_;
  frame_packet.packetno = packet_count_;
  frame_packet.packet = opus_frame_bytes;
  frame_packet.bytes = opus_bytes_length;
  // Add the data packet into the stream.
  packet_count_++;
  ogg_stream_packetin(&stream_, &frame_packet);

獲取輸出數(shù)據(jù)

void OggOpusEncoder::AppendOggStateToBuffer(std::vector<unsigned char>* buffer,
                                            bool flush_ogg_stream) {
  int (*write_fun)(ogg_stream_state*, ogg_page*) =
      flush_ogg_stream ? &ogg_stream_flush : &ogg_stream_pageout;
  while (write_fun(&stream_, &page_) != 0) {
    const int initial_size = buffer->size();
    buffer->resize(buffer->size() + page_.header_len + page_.body_len);
    memcpy(buffer->data() + initial_size, page_.header, page_.header_len);
    memcpy(buffer->data() + initial_size + page_.header_len, page_.body,
           page_.body_len);
  }
}

解碼相關

基本方法

創(chuàng)建與銷毀

創(chuàng)建
ogg_sync_state ogsync; ogg_sync_init(&ogsync);
銷毀
ogg_sync_clear

遍歷處理數(shù)據(jù)

處理結構

ogg_sync_init(&ogsync);
while(get_next_page(file, &ogsync, &page, &written)) {
    ...
    p->process_page(p, &page);
    ...
    
}
ogg_sync_clear(&ogsync)

寫數(shù)據(jù)到同步器

while((ret = ogg_sync_pageseek(ogsync, page)) <= 0) {
    if(ret < 0) {
        /* unsynced, we jump over bytes to a possible capture - we don't need to read more just yet */
        oi_warn(_("WARNING: Hole in data (%d bytes) found at approximate offset %" I64FORMAT " bytes. Corrupted Ogg.\n"), -ret, *written);
        continue;
    }

    /* zero return, we didn't have enough data to find a whole page, read */
    buffer = ogg_sync_buffer(ogsync, CHUNK);
    bytes = fread(buffer, 1, CHUNK, f);
    if(bytes <= 0) {
        ogg_sync_wrote(ogsync, 0);
        return 0;
    }
    ogg_sync_wrote(ogsync, bytes);
    *written += bytes;
}

文件頭處理示例

//初始化流
ogg_stream_init(&stream->os, serial);
//ogg_stream_init
ogg_stream_pagein(&stream->os, page);
res = ogg_stream_packetout(&stream->os, &packet);
if(res <= 0) {
    oi_warn(_("WARNING: Invalid header page, no packet found\n"));
    null_start(stream);
}
else if(packet.bytes >= 19 && memcmp(packet.packet, "OpusHead", 8)==0)
...

/* re-init, ready for processing */
ogg_stream_clear(&stream->os);
ogg_stream_init(&stream->os, serial);
//此處是為了下次重新解析頭

音頻數(shù)據(jù)解析

音頻數(shù)據(jù)的解析根據(jù)ogg格式也是每個page進行解析

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