A class for high level Matroska reading including resync

src/common/kax_file.cpp

@@ -0,0 +1,190 @@
+/*
+   mkvmerge -- utility for splicing together matroska files
+   from component media subtypes
+
+   Distributed under the GPL
+   see the file COPYING for details
+   or visit http://www.gnu.org/copyleft/gpl.html
+
+   high level Matroska file reader
+
+   Written by Moritz Bunkus <moritz@bunkus.org>.
+*/
+
+#include "os.h"
+
+#include <ebml/EbmlStream.h>
+
+#include "common/kax_file.h"
+#include "common/vint.h"
+
+kax_file_c::kax_file_c(mm_io_cptr &in)
+  : m_in(in)
+  , m_resynced(false)
+  , m_resync_start_pos(0)
+  , m_file_size(m_in->get_size())
+  , m_es(counted_ptr<EbmlStream>(new EbmlStream(*m_in.get_object())))
+{
+}
+
+EbmlElement *
+kax_file_c::read_next_level1_element(uint32_t wanted_id) {
+  m_resynced         = false;
+  m_resync_start_pos = 0;
+
+  bool debug_this    = debugging_requested("kax_file") || debugging_requested("kax_file_read_next");
+
+  // Enough space left to read the ID?
+  int64_t remaining_size = m_file_size - m_in->getFilePointer();
+  if (4 > remaining_size)
+    return NULL;
+
+  // Easiest case: next level 1 element following the previous one
+  // without any element inbetween.
+  int64_t search_start_pos = m_in->getFilePointer();
+  uint32_t actual_id       = m_in->read_uint32_be();
+  m_in->setFilePointer(search_start_pos, seek_beginning);
+
+  if (debug_this)
+    mxinfo(boost::format("kax_file::read_next_level1_element(): SEARCH AT %1% ACT ID %|2$04x|\n") % search_start_pos % actual_id);
+
+  if ((wanted_id == actual_id) || ((0 == wanted_id) && is_level1_element_id(actual_id))) {
+    int upper_lvl_el = 0;
+    EbmlElement *l1  = m_es->FindNextElement(KaxSegment::ClassInfos.Context, upper_lvl_el, 0xFFFFFFFFL, true);
+    EbmlElement *l2  = NULL;
+
+    l1->Read(*m_es.get_object(), KaxCluster::ClassInfos.Context, upper_lvl_el, l2, true);
+    delete l2;
+
+    return l1;
+  }
+
+  // If a specific level 1 is wanted then look for next ID by skipping
+  // other known level 1 elements. If that files fallback to a
+  // byte-for-byte search for the ID.
+  if ((0 != wanted_id) && is_level1_element_id(actual_id)) {
+    m_in->setFilePointer(search_start_pos, seek_beginning);
+    int upper_lvl_el = 0;
+    EbmlElement *l1  = m_es->FindNextElement(KaxSegment::ClassInfos.Context, upper_lvl_el, 0xFFFFFFFFL, true);
+
+    if ((NULL != l1) && (EbmlId(*l1).Value == actual_id)) {
+      // Found another level 1 element, just as we thought we
+      // would. Seek to its end and restart the search from there.
+
+      int upper_lvl_el = 0;
+      EbmlElement *l2  = NULL;
+      l1->Read(*m_es.get_object(), KaxSegment::ClassInfos.Context, upper_lvl_el, l2, true);
+      bool ok = m_in->setFilePointer2(l1->GetElementPosition() + l1->ElementSize(), seek_beginning);
+      delete l2;
+
+      if (debug_this)
+        mxinfo(boost::format("kax_file::read_next_level1_element(): other level 1 element %1% new pos %2% fsize %3% epos %4% esize %5%\n")
+               % l1->Generic().DebugName  % (l1->GetElementPosition() + l1->ElementSize()) % m_file_size
+               % l1->GetElementPosition() % l1->ElementSize());
+
+      return ok ? read_next_level1_element(wanted_id) : NULL;
+    }
+  }
+
+  // Last case: no valid ID found. Try a byte-for-byte search for the
+  // next wanted/level 1 ID. Also try to locate at least three valid
+  // ID/sizes, not just one ID.
+  m_in->setFilePointer(search_start_pos, seek_beginning);
+  return resync_to_level1_element(wanted_id);
+}
+
+bool
+kax_file_c::is_level1_element_id(const EbmlId &id) const {
+  return is_level1_element_id(static_cast<uint32_t>(id.Value));
+}
+
+bool
+kax_file_c::is_level1_element_id(uint32_t id) const {
+  const EbmlSemanticContext &context = KaxSegment::ClassInfos.Context;
+  for (int segment_idx = 0; context.Size > segment_idx; ++segment_idx)
+    if (context.MyTable[segment_idx].GetCallbacks.GlobalId.Value == id)
+      return true;
+
+  return false;
+}
+
+EbmlElement *
+kax_file_c::resync_to_level1_element(uint32_t wanted_id) {
+  m_resynced         = true;
+  m_resync_start_pos = m_in->getFilePointer();
+
+  bool debug_this    = debugging_requested("kax_file") || debugging_requested("kax_file_resync");
+  uint32_t actual_id = m_in->read_uint32_be();
+
+  while (m_in->getFilePointer() < m_file_size) {
+    actual_id = (actual_id << 8) | m_in->read_uint8();
+
+    if (   ((0 != wanted_id) && (wanted_id != actual_id))
+        || ((0 == wanted_id) && !is_level1_element_id(actual_id)))
+      continue;
+
+    int64_t current_start_pos = m_in->getFilePointer() - 4;
+    int64_t element_pos       = current_start_pos;
+    unsigned int num_headers  = 1;
+
+    if (debug_this)
+      mxinfo(boost::format("kax_file::resync_to_level1_element(): byte-for-byte search, found level 1 ID %|2$04x| at %1%\n") % current_start_pos % actual_id);
+
+    try {
+      unsigned int idx;
+      for (idx = 0; 3 > idx; ++idx) {
+        vint_c length = vint_c::read(m_in);
+
+        if (debug_this)
+          mxinfo(boost::format("kax_file::resync_to_level1_element():   read ebml length %1%/%2% valid? %3%\n") % length.m_value % length.m_coded_size % length.is_valid());
+
+        if (   !length.is_valid()
+            || ((element_pos + length.m_value + length.m_coded_size + 2 * 4) >= m_file_size)
+            || !m_in->setFilePointer2(element_pos + 4 + length.m_value + length.m_coded_size, seek_beginning))
+          break;
+
+        element_pos      = m_in->getFilePointer();
+        uint32_t next_id = m_in->read_uint32_be();
+
+        if (debug_this)
+          mxinfo(boost::format("kax_file::resync_to_level1_element():   next ID is %|1$04x| at %2%\n") % next_id % element_pos);
+
+        if (   ((0 != wanted_id) && (wanted_id != next_id))
+            || ((0 == wanted_id) && !is_level1_element_id(next_id)))
+          break;
+
+        ++num_headers;
+      }
+    } catch (...) {
+    }
+
+    if (4 == num_headers) {
+      m_in->setFilePointer(current_start_pos, seek_beginning);
+      return read_next_level1_element(wanted_id);
+    }
+
+    m_in->setFilePointer(current_start_pos + 4, seek_beginning);
+  }
+
+  return NULL;
+}
+
+KaxCluster *
+kax_file_c::resync_to_cluster() {
+  return static_cast<KaxCluster *>(resync_to_level1_element(KaxCluster::ClassInfos.GlobalId.Value));
+}
+
+KaxCluster *
+kax_file_c::read_next_cluster() {
+  return static_cast<KaxCluster *>(read_next_level1_element(KaxCluster::ClassInfos.GlobalId.Value));
+}
+
+bool
+kax_file_c::was_resynced() const {
+  return m_resynced;
+}
+
+int64_t
+kax_file_c::get_resync_start_pos() const {
+  return m_resync_start_pos;
+}

src/common/kax_file.h

@@ -0,0 +1,51 @@
+/*
+   mkvmerge -- utility for splicing together matroska files
+   from component media subtypes
+
+   Distributed under the GPL
+   see the file COPYING for details
+   or visit http://www.gnu.org/copyleft/gpl.html
+
+   high level Matroska file reader
+
+   Written by Moritz Bunkus <moritz@bunkus.org>.
+*/
+
+#ifndef __MTX_COMMON_KAX_FILE_H
+#define __MTX_COMMON_KAX_FILE_H
+
+#include "os.h"
+
+#include <matroska/KaxSegment.h>
+#include <matroska/KaxCluster.h>
+
+#include "common/mm_io.h"
+
+using namespace libebml;
+using namespace libmatroska;
+
+class kax_file_c {
+protected:
+  mm_io_cptr m_in;
+  bool m_resynced;
+  int64_t m_resync_start_pos, m_file_size;
+  counted_ptr<EbmlStream> m_es;
+
+public:
+  kax_file_c(mm_io_cptr &in);
+
+
+  virtual bool was_resynced() const;
+  virtual int64_t get_resync_start_pos() const;
+  virtual bool is_level1_element_id(const EbmlId &id) const;
+  virtual bool is_level1_element_id(uint32_t id) const;
+
+  virtual EbmlElement *read_next_level1_element(uint32_t wanted_id = 0);
+  virtual KaxCluster *read_next_cluster();
+
+  virtual EbmlElement *resync_to_level1_element(uint32_t wanted_id = 0);
+  virtual KaxCluster *resync_to_cluster();
+};
+typedef counted_ptr<kax_file_c> kax_file_cptr;
+
+#endif  // __MTX_COMMON_KAX_FILE_H