LibVideo: Parse the duration of Matroska files

Author: https://github.com/Zaggy1024
Commit: https://github.com/SerenityOS/serenity/commit/3a2f6c700d
Pull-request: https://github.com/SerenityOS/serenity/pull/15851

Userland/Libraries/LibVideo/MatroskaDocument.h

@@ -30,11 +30,14 @@ public:
     void set_muxing_app(String muxing_app) { m_muxing_app = move(muxing_app); }
     Utf8View writing_app() const { return Utf8View(m_writing_app); }
     void set_writing_app(String writing_app) { m_writing_app = move(writing_app); }
+    Optional<double> duration() const { return m_duration; }
+    void set_duration(double duration) { m_duration.emplace(duration); }
 
 private:
     u64 m_timestamp_scale { 1'000'000 };
     String m_muxing_app;
     String m_writing_app;
+    Optional<double> m_duration;
 };
 
 class TrackEntry {

Userland/Libraries/LibVideo/MatroskaReader.cpp

@@ -26,6 +26,7 @@ constexpr u32 CLUSTER_ELEMENT_ID = 0x1F43B675;
 constexpr u32 TIMESTAMP_SCALE_ID = 0x2AD7B1;
 constexpr u32 MUXING_APP_ID = 0x4D80;
 constexpr u32 WRITING_APP_ID = 0x5741;
+constexpr u32 DURATION_ID = 0x4489;
 
 // Tracks
 constexpr u32 TRACK_ENTRY_ID = 0xAE;
@@ -195,6 +196,11 @@ OwnPtr<SegmentInformation> MatroskaReader::parse_information()
             CHECK_HAS_VALUE(writing_app);
             segment_information->set_writing_app(writing_app.value());
             dbgln_if(MATROSKA_DEBUG, "Read WritingApp attribute: {}", writing_app.value());
+        } else if (element_id == DURATION_ID) {
+            auto duration = read_float_element();
+            CHECK_HAS_VALUE(duration);
+            segment_information->set_duration(duration.value());
+            dbgln_if(MATROSKA_DEBUG, "Read Duration attribute: {}", duration.value());
         } else {
             return read_unknown_element();
         }
@@ -516,6 +522,30 @@ Optional<u64> MatroskaReader::read_u64_element()
     return result;
 }
 
+Optional<double> MatroskaReader::read_float_element()
+{
+    auto length = m_streamer.read_variable_size_integer();
+    if (!length.has_value() || m_streamer.remaining() < length.value())
+        return {};
+    if (length != 4u && length != 8u)
+        return {};
+
+    union {
+        u64 value;
+        float float_value;
+        double double_value;
+    } read_data;
+    read_data.value = 0;
+    for (size_t i = 0; i < length.value(); i++) {
+        if (!m_streamer.has_octet())
+            return {};
+        read_data.value = (read_data.value << 8u) + m_streamer.read_octet();
+    }
+    if (length == 4u)
+        return read_data.float_value;
+    return read_data.double_value;
+}
+
 bool MatroskaReader::read_unknown_element()
 {
     auto element_length = m_streamer.read_variable_size_integer();

Userland/Libraries/LibVideo/MatroskaReader.h

@@ -166,6 +166,7 @@ private:
 
     Optional<String> read_string_element();
     Optional<u64> read_u64_element();
+    Optional<double> read_float_element();
     bool read_unknown_element();
 
     Streamer m_streamer;