From 789bc99b8d417f3698f6012f34da3f67d0b07dc8 Mon Sep 17 00:00:00 2001
From: Zaggy1024 <zaggy1024@gmail.com>
Date: Sun, 12 Feb 2023 00:48:27 -0600
Subject: [PATCH] LibVideo: Add StartingStateHandler to prepare the first
 frames of video

This new state handler will retrieve and display the first frame, while
ensuring that playback can start as soon as possible by buffering two
frames on top of the first frame for the PlayingStateHandler to set its
next frame timer by.
---
 .../Libraries/LibVideo/PlaybackManager.cpp    | 59 ++++++++++++++++++-
 Userland/Libraries/LibVideo/PlaybackManager.h |  1 +
 2 files changed, 58 insertions(+), 2 deletions(-)

diff --git a/Userland/Libraries/LibVideo/PlaybackManager.cpp b/Userland/Libraries/LibVideo/PlaybackManager.cpp
index 777f654449..f854dd43a7 100644
--- a/Userland/Libraries/LibVideo/PlaybackManager.cpp
+++ b/Userland/Libraries/LibVideo/PlaybackManager.cpp
@@ -277,6 +277,61 @@ PlaybackManager& PlaybackManager::PlaybackStateHandler::manager() const
     return m_manager;
 }
 
+class PlaybackManager::StartingStateHandler : public PlaybackManager::PlaybackStateHandler {
+public:
+    StartingStateHandler(PlaybackManager& manager, bool playing)
+        : PlaybackStateHandler(manager)
+        , m_playing(playing)
+    {
+    }
+    ~StartingStateHandler() override = default;
+
+private:
+    ErrorOr<void> on_enter() override
+    {
+        return on_timer_callback();
+    }
+
+    StringView name() override { return "Starting"sv; }
+
+    ErrorOr<void> on_timer_callback() override
+    {
+        // Once we're threaded, instead of checking for the count here we can just mutex
+        // in the queue until we display the first and then again for the second to store it.
+        if (manager().m_frame_queue->size() < 3) {
+            manager().m_decode_timer->start(0);
+            manager().start_timer(0);
+            return {};
+        }
+
+        auto frame_to_display = manager().m_frame_queue->dequeue();
+        manager().m_last_present_in_media_time = frame_to_display.timestamp();
+        if (manager().dispatch_frame_queue_item(move(frame_to_display)))
+            return {};
+
+        manager().m_next_frame.emplace(manager().m_frame_queue->dequeue());
+        manager().m_decode_timer->start(0);
+        dbgln_if(PLAYBACK_MANAGER_DEBUG, "Displayed frame at {}ms, emplaced second frame at {}ms, finishing start now", manager().m_last_present_in_media_time.to_milliseconds(), manager().m_next_frame->timestamp().to_milliseconds());
+        if (!m_playing)
+            return replace_handler_and_delete_this<PausedStateHandler>();
+        return replace_handler_and_delete_this<PlayingStateHandler>();
+    }
+
+    ErrorOr<void> play() override
+    {
+        m_playing = true;
+        return {};
+    }
+    bool is_playing() override { return m_playing; };
+    ErrorOr<void> pause() override
+    {
+        m_playing = false;
+        return {};
+    }
+
+    bool m_playing;
+};
+
 class PlaybackManager::PlayingStateHandler : public PlaybackManager::PlaybackStateHandler {
 public:
     PlayingStateHandler(PlaybackManager& manager)
@@ -320,7 +375,7 @@ private:
             manager().start_timer(max(static_cast<int>(frame_time_ms), 0));
         };
 
-        if (manager().m_next_frame.has_value() && manager().m_next_frame->timestamp() < current_time()) {
+        if (manager().m_next_frame.has_value() && current_time() < manager().m_next_frame->timestamp()) {
             dbgln_if(PLAYBACK_MANAGER_DEBUG, "Current time {}ms is too early to present the next frame at {}ms, delaying", current_time().to_milliseconds(), manager().m_next_frame->timestamp().to_milliseconds());
             set_presentation_timer();
             return {};
@@ -600,7 +655,7 @@ private:
         auto start_timestamp = manager().seek_demuxer_to_most_recent_keyframe(Time::zero());
         VERIFY(start_timestamp.has_value());
         manager().m_last_present_in_media_time = start_timestamp.release_value();
-        return replace_handler_and_delete_this<PlayingStateHandler>();
+        return replace_handler_and_delete_this<StartingStateHandler>(true);
     }
     bool is_playing() override { return false; };
 };
diff --git a/Userland/Libraries/LibVideo/PlaybackManager.h b/Userland/Libraries/LibVideo/PlaybackManager.h
index 5082049afe..f71cfbb726 100644
--- a/Userland/Libraries/LibVideo/PlaybackManager.h
+++ b/Userland/Libraries/LibVideo/PlaybackManager.h
@@ -114,6 +114,7 @@ public:
 
 private:
     class PlaybackStateHandler;
+    class StartingStateHandler;
     class PlayingStateHandler;
     class PausedStateHandler;
     class BufferingStateHandler;