shaka-packager/packager/mpd/base/mpd_builder.cc

// Copyright 2014 Google Inc. All rights reserved.
//
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file or at
// https://developers.google.com/open-source/licenses/bsd

#include "packager/mpd/base/mpd_builder.h"

#include "packager/base/files/file_path.h"
#include "packager/base/logging.h"
#include "packager/base/strings/string_number_conversions.h"
#include "packager/base/strings/stringprintf.h"
#include "packager/base/synchronization/lock.h"
#include "packager/base/time/default_clock.h"
#include "packager/base/time/time.h"
#include "packager/mpd/base/adaptation_set.h"
#include "packager/mpd/base/mpd_utils.h"
#include "packager/mpd/base/period.h"
#include "packager/mpd/base/xml/xml_node.h"
#include "packager/version/version.h"

namespace shaka {

using base::FilePath;
using xml::XmlNode;

namespace {

void AddMpdNameSpaceInfo(XmlNode* mpd) {
  DCHECK(mpd);

  static const char kXmlNamespace[] = "urn:mpeg:dash:schema:mpd:2011";
  static const char kXmlNamespaceXsi[] =
      "http://www.w3.org/2001/XMLSchema-instance";
  static const char kXmlNamespaceXlink[] = "http://www.w3.org/1999/xlink";
  static const char kDashSchemaMpd2011[] =
      "urn:mpeg:dash:schema:mpd:2011 DASH-MPD.xsd";
  static const char kCencNamespace[] = "urn:mpeg:cenc:2013";

  mpd->SetStringAttribute("xmlns", kXmlNamespace);
  mpd->SetStringAttribute("xmlns:xsi", kXmlNamespaceXsi);
  mpd->SetStringAttribute("xmlns:xlink", kXmlNamespaceXlink);
  mpd->SetStringAttribute("xsi:schemaLocation", kDashSchemaMpd2011);
  mpd->SetStringAttribute("xmlns:cenc", kCencNamespace);
}

bool IsPeriodNode(xmlNodePtr node) {
  DCHECK(node);
  int kEqual = 0;
  return xmlStrcmp(node->name, reinterpret_cast<const xmlChar*>("Period")) ==
         kEqual;
}

// Find the first <Period> element. This does not recurse down the tree,
// only checks direct children. Returns the pointer to Period element on
// success, otherwise returns false.
// As noted here, we must traverse.
// http://www.xmlsoft.org/tutorial/ar01s04.html
xmlNodePtr FindPeriodNode(XmlNode* xml_node) {
  for (xmlNodePtr node = xml_node->GetRawPtr()->xmlChildrenNode; node != NULL;
       node = node->next) {
    if (IsPeriodNode(node))
      return node;
  }

  return NULL;
}

bool Positive(double d) {
  return d > 0.0;
}

// Return current time in XML DateTime format. The value is in UTC, so the
// string ends with a 'Z'.
std::string XmlDateTimeNowWithOffset(
    int32_t offset_seconds,
    base::Clock* clock) {
  base::Time time = clock->Now();
  time += base::TimeDelta::FromSeconds(offset_seconds);
  base::Time::Exploded time_exploded;
  time.UTCExplode(&time_exploded);

  return base::StringPrintf("%4d-%02d-%02dT%02d:%02d:%02dZ", time_exploded.year,
                            time_exploded.month, time_exploded.day_of_month,
                            time_exploded.hour, time_exploded.minute,
                            time_exploded.second);
}

void SetIfPositive(const char* attr_name, double value, XmlNode* mpd) {
  if (Positive(value)) {
    mpd->SetStringAttribute(attr_name, SecondsToXmlDuration(value));
  }
}

std::string MakePathRelative(const std::string& media_path,
                             const FilePath& parent_path) {
  FilePath relative_path;
  const FilePath child_path = FilePath::FromUTF8Unsafe(media_path);
  const bool is_child =
      parent_path.AppendRelativePath(child_path, &relative_path);
  if (!is_child)
    relative_path = child_path;
  return relative_path.NormalizePathSeparatorsTo('/').AsUTF8Unsafe();
}

// Spooky static initialization/cleanup of libxml.
class LibXmlInitializer {
 public:
  LibXmlInitializer() : initialized_(false) {
    base::AutoLock lock(lock_);
    if (!initialized_) {
      xmlInitParser();
      initialized_ = true;
    }
  }

  ~LibXmlInitializer() {
    base::AutoLock lock(lock_);
    if (initialized_) {
      xmlCleanupParser();
      initialized_ = false;
    }
  }

 private:
  base::Lock lock_;
  bool initialized_;

  DISALLOW_COPY_AND_ASSIGN(LibXmlInitializer);
};

}  // namespace

MpdBuilder::MpdBuilder(const MpdOptions& mpd_options)
    : mpd_options_(mpd_options), clock_(new base::DefaultClock()) {}

MpdBuilder::~MpdBuilder() {}

void MpdBuilder::AddBaseUrl(const std::string& base_url) {
  base_urls_.push_back(base_url);
}

Period* MpdBuilder::AddPeriod() {
  periods_.emplace_back(new Period(mpd_options_, &adaptation_set_counter_,
                                   &representation_counter_));
  return periods_.back().get();
}

bool MpdBuilder::ToString(std::string* output) {
  DCHECK(output);
  static LibXmlInitializer lib_xml_initializer;

  xml::scoped_xml_ptr<xmlDoc> doc(GenerateMpd());
  if (!doc)
    return false;

  static const int kNiceFormat = 1;
  int doc_str_size = 0;
  xmlChar* doc_str = nullptr;
  xmlDocDumpFormatMemoryEnc(doc.get(), &doc_str, &doc_str_size, "UTF-8",
                            kNiceFormat);
  output->assign(doc_str, doc_str + doc_str_size);
  xmlFree(doc_str);

  // Cleanup, free the doc.
  doc.reset();
  return true;
}

xmlDocPtr MpdBuilder::GenerateMpd() {
  // Setup nodes.
  static const char kXmlVersion[] = "1.0";
  xml::scoped_xml_ptr<xmlDoc> doc(xmlNewDoc(BAD_CAST kXmlVersion));
  XmlNode mpd("MPD");

  // Add baseurls to MPD.
  for (const std::string& base_url : base_urls_) {
    XmlNode xml_base_url("BaseURL");
    xml_base_url.SetContent(base_url);

    if (!mpd.AddChild(xml_base_url.PassScopedPtr()))
      return nullptr;
  }

  for (const auto& period : periods_) {
    xml::scoped_xml_ptr<xmlNode> period_node(period->GetXml());
    if (!period_node || !mpd.AddChild(std::move(period_node)))
      return nullptr;
  }

  AddMpdNameSpaceInfo(&mpd);

  static const char kOnDemandProfile[] =
      "urn:mpeg:dash:profile:isoff-on-demand:2011";
  static const char kLiveProfile[] =
      "urn:mpeg:dash:profile:isoff-live:2011";
  switch (mpd_options_.dash_profile) {
    case DashProfile::kOnDemand:
      mpd.SetStringAttribute("profiles", kOnDemandProfile);
      break;
    case DashProfile::kLive:
      mpd.SetStringAttribute("profiles", kLiveProfile);
      break;
    default:
      NOTREACHED() << "Unknown DASH profile: "
                   << static_cast<int>(mpd_options_.dash_profile);
      break;
  }

  AddCommonMpdInfo(&mpd);
  switch (mpd_options_.mpd_type) {
    case MpdType::kStatic:
      AddStaticMpdInfo(&mpd);
      break;
    case MpdType::kDynamic:
      AddDynamicMpdInfo(&mpd);
      break;
    default:
      NOTREACHED() << "Unknown MPD type: "
                   << static_cast<int>(mpd_options_.mpd_type);
      break;
  }

  DCHECK(doc);
  const std::string version = GetPackagerVersion();
  if (!version.empty()) {
    std::string version_string =
        base::StringPrintf("Generated with %s version %s",
                           GetPackagerProjectUrl().c_str(), version.c_str());
    xml::scoped_xml_ptr<xmlNode> comment(
        xmlNewDocComment(doc.get(), BAD_CAST version_string.c_str()));
    xmlDocSetRootElement(doc.get(), comment.get());
    xmlAddSibling(comment.release(), mpd.Release());
  } else {
    xmlDocSetRootElement(doc.get(), mpd.Release());
  }
  return doc.release();
}

void MpdBuilder::AddCommonMpdInfo(XmlNode* mpd_node) {
  if (Positive(mpd_options_.mpd_params.min_buffer_time)) {
    mpd_node->SetStringAttribute(
        "minBufferTime",
        SecondsToXmlDuration(mpd_options_.mpd_params.min_buffer_time));
  } else {
    LOG(ERROR) << "minBufferTime value not specified.";
    // TODO(tinskip): Propagate error.
  }
}

void MpdBuilder::AddStaticMpdInfo(XmlNode* mpd_node) {
  DCHECK(mpd_node);
  DCHECK_EQ(MpdType::kStatic, mpd_options_.mpd_type);

  static const char kStaticMpdType[] = "static";
  mpd_node->SetStringAttribute("type", kStaticMpdType);
  mpd_node->SetStringAttribute(
      "mediaPresentationDuration",
      SecondsToXmlDuration(GetStaticMpdDuration(mpd_node)));
}

void MpdBuilder::AddDynamicMpdInfo(XmlNode* mpd_node) {
  DCHECK(mpd_node);
  DCHECK_EQ(MpdType::kDynamic, mpd_options_.mpd_type);

  static const char kDynamicMpdType[] = "dynamic";
  mpd_node->SetStringAttribute("type", kDynamicMpdType);

  // No offset from NOW.
  mpd_node->SetStringAttribute("publishTime",
                               XmlDateTimeNowWithOffset(0, clock_.get()));

  // 'availabilityStartTime' is required for dynamic profile. Calculate if
  // not already calculated.
  if (availability_start_time_.empty()) {
    double earliest_presentation_time;
    if (GetEarliestTimestamp(&earliest_presentation_time)) {
      availability_start_time_ = XmlDateTimeNowWithOffset(
          -std::ceil(earliest_presentation_time), clock_.get());
    } else {
      LOG(ERROR) << "Could not determine the earliest segment presentation "
                    "time for availabilityStartTime calculation.";
      // TODO(tinskip). Propagate an error.
    }
  }
  if (!availability_start_time_.empty())
    mpd_node->SetStringAttribute("availabilityStartTime",
                                 availability_start_time_);

  if (Positive(mpd_options_.mpd_params.minimum_update_period)) {
    mpd_node->SetStringAttribute(
        "minimumUpdatePeriod",
        SecondsToXmlDuration(mpd_options_.mpd_params.minimum_update_period));
  } else {
    LOG(WARNING) << "The profile is dynamic but no minimumUpdatePeriod "
                    "specified.";
  }

  SetIfPositive("timeShiftBufferDepth",
                mpd_options_.mpd_params.time_shift_buffer_depth, mpd_node);
  SetIfPositive("suggestedPresentationDelay",
                mpd_options_.mpd_params.suggested_presentation_delay, mpd_node);
}

float MpdBuilder::GetStaticMpdDuration(XmlNode* mpd_node) {
  DCHECK(mpd_node);
  DCHECK_EQ(MpdType::kStatic, mpd_options_.mpd_type);

  // Attribute mediaPresentationDuration must be present for 'static' MPD. So
  // setting "PT0S" is required even if none of the representaions have duration
  // attribute.
  float max_duration = 0.0f;

  xmlNodePtr period_node = FindPeriodNode(mpd_node);
  if (!period_node) {
    LOG(WARNING) << "No Period node found. Set MPD duration to 0.";
    return 0.0f;
  }

  DCHECK(IsPeriodNode(period_node));
  // TODO(kqyang): Why don't we iterate the C++ classes instead of iterating XML
  // elements?
  // TODO(kqyang): Verify if this works for static + live profile.
  for (xmlNodePtr adaptation_set = xmlFirstElementChild(period_node);
       adaptation_set; adaptation_set = xmlNextElementSibling(adaptation_set)) {
    for (xmlNodePtr representation = xmlFirstElementChild(adaptation_set);
         representation;
         representation = xmlNextElementSibling(representation)) {
      float duration = 0.0f;
      if (GetDurationAttribute(representation, &duration)) {
        max_duration = max_duration > duration ? max_duration : duration;

        // 'duration' attribute is there only to help generate MPD, not
        // necessary for MPD, remove the attribute.
        xmlUnsetProp(representation, BAD_CAST "duration");
      }
    }
  }

  return max_duration;
}

bool MpdBuilder::GetEarliestTimestamp(double* timestamp_seconds) {
  DCHECK(timestamp_seconds);
  DCHECK(!periods_.empty());
  return periods_.front()->GetEarliestTimestamp(timestamp_seconds);
}

void MpdBuilder::MakePathsRelativeToMpd(const std::string& mpd_path,
                                        MediaInfo* media_info) {
  DCHECK(media_info);
  const std::string kFileProtocol("file://");
  std::string mpd_file_path = (mpd_path.find(kFileProtocol) == 0)
                                  ? mpd_path.substr(kFileProtocol.size())
                                  : mpd_path;

  if (!mpd_file_path.empty()) {
    const FilePath mpd_dir(FilePath::FromUTF8Unsafe(mpd_file_path)
                               .DirName()
                               .AsEndingWithSeparator());
    if (!mpd_dir.empty()) {
      if (media_info->has_media_file_name()) {
        media_info->set_media_file_name(
            MakePathRelative(media_info->media_file_name(), mpd_dir));
      }
      if (media_info->has_init_segment_name()) {
        media_info->set_init_segment_name(
            MakePathRelative(media_info->init_segment_name(), mpd_dir));
      }
      if (media_info->has_segment_template()) {
        media_info->set_segment_template(
            MakePathRelative(media_info->segment_template(), mpd_dir));
      }
    }
  }
}

}  // namespace shaka