如何从ogg/opus文件中逐个读取OPUS数据包

Question

我需要从ogg/opus文件中一个接一个地读取OPUS数据包，并在没有解码的情况下以OPUS格式进一步发送它们。我正在研究PCM库，但是opusfile和示例相当复杂，并且更多地集中在解码文件和获得结果的PCM上。有没有办法用这个库实现我想要的东西？如果不是，我还有其他选择吗？

Answer 1

libogg可以用来解析Ogg Opus文件的“页面”，然后可以从这些页面中提取操作“数据包”。请注意，数据包可能会跨越多个页面，但我个人在测试opusenc创建的文件时没有遇到过这种情况。您也可以手动解析页面(请参阅Splitting an Ogg Opus File stream)

我建议先阅读Opus文件规范(RFC7845)的基础知识，以了解文件结构。https://opus-codec.org/docs/

Answer 2

我想我来晚了一点。我有非常相似的用例，我想从ogg opus文件中提取opus包。我找到了这个答案

https://stackoverflow.com/a/26285277/10110652

下面的代码将帮助您在while循环内的'nextPacket‘byteArray中获得opus数据包(没有解码为pcm)

File audioFile = null; 
    try {
        audioFile = new File("xyz.ogg"); //input ogg opus file
        oggFile = new FileStream(new RandomAccessFile(audioFile, "r"));

        for (LogicalOggStream stream : (Collection<LogicalOggStream>) oggFile.getLogicalStreams()) {
            byte[] nextPacket = stream.getNextOggPacket();
            while (nextPacket != null) {
                    //nextPacket here contains opus packet
                    //do what ever you want to do with this packet
                 
                nextPacket = stream.getNextOggPacket();
            }
        }

    } catch (EndOfOggStreamException e) {
        System.out.println("End of File");
        //file usually get over by raising this exception while execution getNextOggPacket()
    }

同样的程序可以用来提取ogg容器中的vorbis编码的数据包，即ogg vorbis文件。

编码快乐！

Answer 3

您可以使用libogg访问Opus数据包。不幸的是，它并不比opusfile简单得多。在C-ish伪代码中，一般流程是：

readPage(ogg_sync_state* syncState, ogg_page* page, file) {
  while ((ogg_sync_pageout(syncState, page) != 1) && file is good) {
    buffer = ogg_sync_buffer(syncState, yourMaxReadSize);
    bytesActuallyRead = read(file, buffer, yourMaxReadSize);
    ogg_sync_wrote(syncState, bytesActuallyReadFromFile); //tell the syncState how many bytes were actually read
  } //now we have a page, or the file is done
}

read() {
  ogg_sync_state oggSyncState;
  ogg_stream_state oggStreamState;
  ogg_page oggPage;
  ogg_packet oggPacket;

  open file;

  while (file is good) {
    readPage(&oggSyncState, &oggPage);
    if (ogg_page_bos(&oggPage)) {
      sn = ogg_page_serialno(&oggPage); //you can remember this serial number and check it on every page for robustness
      ogg_stream_init(&oggStreamState, sn);
    } 
    ogg_stream_pagein(&oggStreamState, &oggPage);
    while (ogg_stream_packetout(&oggStreamState, &oggPacket) != 0) {
      //check if it's a header packet, skip if so.
      //See https://tools.ietf.org/html/rfc7845.html#section-5 to see how to identify a header packet
      //Else it must be data
      do something with the buffer oggPacket.packet with size oggPacket.bytes
    }
    readPage(&oggSyncState, &oggPage, file);
    ogg_stream_pagein(&oggStreamState, &oggPage_);
  }
}

readPage从文件中提取一串字节(yourMaxReadSize)到oggSyncState结构中，然后逐个提取页面。在read中，数据包是逐个从页面中提取的。