Ogg media container file: C++/STL parsing library

Ogg is a popular media container format, which provides basic streaming / buffering mechanisms and is content-agnostic. Most popular codecs that are used within Ogg streams are Vorbis (thus making Ogg/Vorbis streams) and Theora (Ogg/Theora).

Ogg stream is a sequence Ogg pages. They can be read sequentially, or one can jump into arbitrary stream location and scan for "OggS" sync code to find the beginning of a new Ogg page and continue decoding the stream contents from that one.

File extension

["ogg", "ogv", "oga", "spx", "ogx"]

KS implementation details

License: CC0-1.0

This page hosts a formal specification of Ogg media container file using Kaitai Struct. This specification can be automatically translated into a variety of programming languages to get a parsing library.

Usage

Using Kaitai Struct in C++/STL usually consists of 3 steps.

  1. We need to create an STL input stream (std::istream).
    • One can open a stream for reading from a local file:
      #include <fstream>
      
      std::ifstream is("path/to/local/file.["ogg", "ogv", "oga", "spx", "ogx"]", std::ifstream::binary);
    • Or one can prepare a stream for reading from existing std::string str:
      #include <sstream>
      
      std::istringstream is(str);
    • Or one can parse arbitrary char* buffer in memory, given that we know its size:
      #include <sstream>
      
      const char buf[] = { ... };
      std::string str(buf, sizeof buf);
      std::istringstream is(str);
  2. We need to wrap our input stream into Kaitai stream:
    #include <kaitai/kaitaistream.h>
    
    kaitai::kstream ks(&is);
  3. And finally, we can invoke the parsing:
    ogg_t data(&ks);

After that, one can get various attributes from the structure by invoking getter methods like:

data.pages() // => get pages

C++/STL source code to parse Ogg media container file

ogg.h

#ifndef OGG_H_
#define OGG_H_

// This is a generated file! Please edit source .ksy file and use kaitai-struct-compiler to rebuild

#include "kaitai/kaitaistruct.h"

#include <stdint.h>
#include <vector>

#if KAITAI_STRUCT_VERSION < 7000L
#error "Incompatible Kaitai Struct C++/STL API: version 0.7 or later is required"
#endif

/**
 * Ogg is a popular media container format, which provides basic
 * streaming / buffering mechanisms and is content-agnostic. Most
 * popular codecs that are used within Ogg streams are Vorbis (thus
 * making Ogg/Vorbis streams) and Theora (Ogg/Theora).
 * 
 * Ogg stream is a sequence Ogg pages. They can be read sequentially,
 * or one can jump into arbitrary stream location and scan for "OggS"
 * sync code to find the beginning of a new Ogg page and continue
 * decoding the stream contents from that one.
 */

class ogg_t : public kaitai::kstruct {

public:
    class page_t;

    ogg_t(kaitai::kstream* p__io, kaitai::kstruct* p__parent = 0, ogg_t* p__root = 0);

private:
    void _read();

public:
    ~ogg_t();

    /**
     * Ogg page is a basic unit of data in an Ogg bitstream, usually
     * it's around 4-8 KB, with a maximum size of 65307 bytes.
     */

    class page_t : public kaitai::kstruct {

    public:

        page_t(kaitai::kstream* p__io, ogg_t* p__parent = 0, ogg_t* p__root = 0);

    private:
        void _read();

    public:
        ~page_t();

    private:
        std::string m_sync_code;
        std::string m_version;
        uint64_t m_reserved1;
        bool m_is_end_of_stream;
        bool m_is_beginning_of_stream;
        bool m_is_continuation;
        uint64_t m_granule_pos;
        uint32_t m_bitstream_serial;
        uint32_t m_page_seq_num;
        uint32_t m_crc32;
        uint8_t m_num_segments;
        std::vector<uint8_t>* m_len_segments;
        std::vector<std::string>* m_segments;
        ogg_t* m__root;
        ogg_t* m__parent;

    public:
        std::string sync_code() const { return m_sync_code; }

        /**
         * Version of the Ogg bitstream format. Currently must be 0.
         */
        std::string version() const { return m_version; }
        uint64_t reserved1() const { return m_reserved1; }

        /**
         * EOS (End Of Stream) mark. This page is the last page in the
         * logical bitstream. The EOS flag must be set on the final page of
         * every logical bitstream, and must not be set on any other page.
         */
        bool is_end_of_stream() const { return m_is_end_of_stream; }

        /**
         * BOS (Beginning Of Stream) mark. This page is the first page in
         * the logical bitstream. The BOS flag must be set on the first
         * page of every logical bitstream, and must not be set on any
         * other page.    
         */
        bool is_beginning_of_stream() const { return m_is_beginning_of_stream; }

        /**
         * The first packet on this page is a continuation of the previous
         * packet in the logical bitstream.
         */
        bool is_continuation() const { return m_is_continuation; }

        /**
         * "Granule position" is the time marker in Ogg files. It is an
         * abstract value, whose meaning is determined by the codec. It
         * may, for example, be a count of the number of samples, the
         * number of frames or a more complex scheme.
         */
        uint64_t granule_pos() const { return m_granule_pos; }

        /**
         * Serial number that identifies a page as belonging to a
         * particular logical bitstream. Each logical bitstream in a file
         * has a unique value, and this field allows implementations to
         * deliver the pages to the appropriate decoder. In a typical
         * Vorbis and Theora file, one stream is the audio (Vorbis), and
         * the other is the video (Theora).
         */
        uint32_t bitstream_serial() const { return m_bitstream_serial; }

        /**
         * Sequential number of page, guaranteed to be monotonically
         * increasing for each logical bitstream. The first page is 0, the
         * second 1, etc. This allows implementations to detect when data
         * has been lost.
         */
        uint32_t page_seq_num() const { return m_page_seq_num; }

        /**
         * This field provides a CRC32 checksum of the data in the entire
         * page (including the page header, calculated with the checksum
         * field set to 0). This allows verification that the data has not
         * been corrupted since it was created. Pages that fail the
         * checksum should be discarded. The checksum is generated using a
         * polynomial value of 0x04C11DB7.
         */
        uint32_t crc32() const { return m_crc32; }

        /**
         * The number of segments that exist in this page. There can be a
         * maximum of 255 segments in any one page.
         */
        uint8_t num_segments() const { return m_num_segments; }

        /**
         * Table of lengths of segments.
         */
        std::vector<uint8_t>* len_segments() const { return m_len_segments; }

        /**
         * Segment content bytes make up the rest of the Ogg page.
         */
        std::vector<std::string>* segments() const { return m_segments; }
        ogg_t* _root() const { return m__root; }
        ogg_t* _parent() const { return m__parent; }
    };

private:
    std::vector<page_t*>* m_pages;
    ogg_t* m__root;
    kaitai::kstruct* m__parent;

public:
    std::vector<page_t*>* pages() const { return m_pages; }
    ogg_t* _root() const { return m__root; }
    kaitai::kstruct* _parent() const { return m__parent; }
};

#endif  // OGG_H_

ogg.cpp

// This is a generated file! Please edit source .ksy file and use kaitai-struct-compiler to rebuild

#include "ogg.h"



ogg_t::ogg_t(kaitai::kstream* p__io, kaitai::kstruct* p__parent, ogg_t* p__root) : kaitai::kstruct(p__io) {
    m__parent = p__parent;
    m__root = this;
    _read();
}

void ogg_t::_read() {
    m_pages = new std::vector<page_t*>();
    {
        int i = 0;
        while (!m__io->is_eof()) {
            m_pages->push_back(new page_t(m__io, this, m__root));
            i++;
        }
    }
}

ogg_t::~ogg_t() {
    for (std::vector<page_t*>::iterator it = m_pages->begin(); it != m_pages->end(); ++it) {
        delete *it;
    }
    delete m_pages;
}

ogg_t::page_t::page_t(kaitai::kstream* p__io, ogg_t* p__parent, ogg_t* p__root) : kaitai::kstruct(p__io) {
    m__parent = p__parent;
    m__root = p__root;
    _read();
}

void ogg_t::page_t::_read() {
    m_sync_code = m__io->ensure_fixed_contents(std::string("\x4F\x67\x67\x53", 4));
    m_version = m__io->ensure_fixed_contents(std::string("\x00", 1));
    m_reserved1 = m__io->read_bits_int(5);
    m_is_end_of_stream = m__io->read_bits_int(1);
    m_is_beginning_of_stream = m__io->read_bits_int(1);
    m_is_continuation = m__io->read_bits_int(1);
    m__io->align_to_byte();
    m_granule_pos = m__io->read_u8le();
    m_bitstream_serial = m__io->read_u4le();
    m_page_seq_num = m__io->read_u4le();
    m_crc32 = m__io->read_u4le();
    m_num_segments = m__io->read_u1();
    int l_len_segments = num_segments();
    m_len_segments = new std::vector<uint8_t>();
    m_len_segments->reserve(l_len_segments);
    for (int i = 0; i < l_len_segments; i++) {
        m_len_segments->push_back(m__io->read_u1());
    }
    int l_segments = num_segments();
    m_segments = new std::vector<std::string>();
    m_segments->reserve(l_segments);
    for (int i = 0; i < l_segments; i++) {
        m_segments->push_back(m__io->read_bytes(len_segments()->at(i)));
    }
}

ogg_t::page_t::~page_t() {
    delete m_len_segments;
    delete m_segments;
}