LibVideo: Give Matroska duration an absolute value getter

Previously, the duration had to be multiplied by timestamp_scale and
converted to a Time object, now SegmentInformation::duration() does it
itself.

Userland/Libraries/LibVideo/Containers/Matroska/Document.h

@@ -31,14 +31,20 @@ 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); }
+    Optional<double> duration_unscaled() const { return m_duration_unscaled; }
+    void set_duration_unscaled(double duration) { m_duration_unscaled.emplace(duration); }
+    Optional<Time> duration() const
+    {
+        if (!duration_unscaled().has_value())
+            return {};
+        return Time::from_nanoseconds(static_cast<i64>(static_cast<double>(timestamp_scale()) * duration_unscaled().value()));
+    }
 
 private:
     u64 m_timestamp_scale { 1'000'000 };
     String m_muxing_app;
     String m_writing_app;
-    Optional<double> m_duration;
+    Optional<double> m_duration_unscaled;
 };
 
 class TrackEntry {

Userland/Libraries/LibVideo/Containers/Matroska/MatroskaDemuxer.cpp

@@ -82,10 +82,8 @@ DecoderErrorOr<NonnullOwnPtr<Sample>> MatroskaDemuxer::get_next_sample_for_track
 
 DecoderErrorOr<Time> MatroskaDemuxer::duration()
 {
-    auto segment_information = TRY(m_reader.segment_information());
-    if (!segment_information.duration().has_value())
-        return Time::zero();
-    return Time::from_nanoseconds(static_cast<i64>(segment_information.duration().value() * segment_information.timestamp_scale()));
+    auto duration = TRY(m_reader.segment_information()).duration();
+    return duration.value_or(Time::zero());
 }
 
 }

Userland/Libraries/LibVideo/Containers/Matroska/Reader.cpp

@@ -270,8 +270,8 @@ static DecoderErrorOr<SegmentInformation> parse_information(Streamer& streamer)
             dbgln_if(MATROSKA_DEBUG, "Read WritingApp attribute: {}", segment_information.writing_app().as_string());
             break;
         case DURATION_ID:
-            segment_information.set_duration(TRY_READ(streamer.read_float()));
-            dbgln_if(MATROSKA_DEBUG, "Read Duration attribute: {}", segment_information.duration().value());
+            segment_information.set_duration_unscaled(TRY_READ(streamer.read_float()));
+            dbgln_if(MATROSKA_DEBUG, "Read Duration attribute: {}", segment_information.duration_unscaled().value());
             break;
         default:
             TRY_READ(streamer.read_unknown_element());