LibVideo: Add a fast seeking mode to seek only to keyframes

Now that we're able to find the nearest keyframe, we can have a fast
seeking mode that only seeks to keyframes, so that it doesn't have to
also decode inter frames until it reaches the timestamp.

The default is still accurate seeking, so that the entire seeking
implementation can be tested.

Userland/Libraries/LibVideo/Containers/Demuxer.h

@@ -28,7 +28,8 @@ public:
         return sample.release_nonnull<VideoSample>();
     }
 
-    virtual DecoderErrorOr<void> seek_to_most_recent_keyframe(Track track, Time timestamp) = 0;
+    // Returns the timestamp of the keyframe that was seeked to.
+    virtual DecoderErrorOr<Time> seek_to_most_recent_keyframe(Track track, Time timestamp) = 0;
 
     virtual DecoderErrorOr<Time> duration() = 0;
 

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

@@ -53,16 +53,17 @@ DecoderErrorOr<MatroskaDemuxer::TrackStatus*> MatroskaDemuxer::get_track_status(
     return &m_track_statuses.get(track).release_value();
 }
 
-DecoderErrorOr<void> MatroskaDemuxer::seek_to_most_recent_keyframe(Track track, Time timestamp)
+DecoderErrorOr<Time> MatroskaDemuxer::seek_to_most_recent_keyframe(Track track, Time timestamp)
 {
     // Removing the track status will cause us to start from the beginning.
     if (timestamp.is_zero()) {
         m_track_statuses.remove(track);
-        return {};
+        return timestamp;
     }
 
     auto& track_status = *TRY(get_track_status(track));
-    return m_reader.seek_to_random_access_point(track_status.iterator, timestamp);
+    TRY(m_reader.seek_to_random_access_point(track_status.iterator, timestamp));
+    return track_status.iterator.last_timestamp();
 }
 
 DecoderErrorOr<NonnullOwnPtr<Sample>> MatroskaDemuxer::get_next_sample_for_track(Track track)

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

@@ -27,7 +27,7 @@ public:
 
     DecoderErrorOr<Vector<Track>> get_tracks_for_type(TrackType type) override;
 
-    DecoderErrorOr<void> seek_to_most_recent_keyframe(Track track, Time timestamp) override;
+    DecoderErrorOr<Time> seek_to_most_recent_keyframe(Track track, Time timestamp) override;
 
     DecoderErrorOr<Time> duration() override;
 

Userland/Libraries/LibVideo/PlaybackManager.cpp

@@ -236,7 +236,10 @@ void PlaybackManager::seek_to_timestamp(Time timestamp)
     m_frame_queue->clear();
     m_next_frame.clear();
     m_skipped_frames = 0;
-    m_seek_to_media_time = timestamp;
+    if (m_seek_mode == SeekMode::Accurate)
+        m_seek_to_media_time = timestamp;
+    else
+        m_seek_to_media_time = result.release_value();
     m_last_present_in_media_time = Time::min();
     m_last_present_in_real_time = Time::zero();
     m_present_timer->stop();

Userland/Libraries/LibVideo/PlaybackManager.h

@@ -94,6 +94,13 @@ using VideoFrameQueue = Queue<FrameQueueItem, FRAME_BUFFER_COUNT>;
 
 class PlaybackManager {
 public:
+    enum class SeekMode {
+        Accurate,
+        Fast,
+    };
+
+    static constexpr SeekMode DEFAULT_SEEK_MODE = SeekMode::Accurate;
+
     static DecoderErrorOr<NonnullOwnPtr<PlaybackManager>> from_file(Core::Object& event_handler, StringView file);
     static DecoderErrorOr<NonnullOwnPtr<PlaybackManager>> from_data(Core::Object& event_handler, Span<u8> data);
 
@@ -108,6 +115,9 @@ public:
     bool is_buffering() const { return m_status == PlaybackStatus::Buffering; }
     bool is_stopped() const { return m_status == PlaybackStatus::Stopped || m_status == PlaybackStatus::Corrupted; }
 
+    SeekMode seek_mode() { return m_seek_mode; }
+    void set_seek_mode(SeekMode mode) { m_seek_mode = mode; }
+
     u64 number_of_skipped_frames() const { return m_skipped_frames; }
 
     void on_decoder_error(DecoderError error);
@@ -136,6 +146,7 @@ private:
     Time m_last_present_in_real_time = Time::zero();
 
     Time m_seek_to_media_time = Time::min();
+    SeekMode m_seek_mode = DEFAULT_SEEK_MODE;
 
     NonnullOwnPtr<Demuxer> m_demuxer;
     Track m_selected_video_track;