Implement seamless ffmpeg playback looping

Users need seamless looping, in other words, looping without
little delays on jumping from the media end to the start.

The only way to make it seamles and smooth is to intrude into the
playback engine. As result, we have just a regular delay between frames
on shifting.

Also, a bunch of adjuscent small improvements have been introduced:
- simplify criteria of the demuxer's buffer size, it was more complex
  and a bit not relevant before. Actually, we need to check
  only max buffering time.
- Improve handling of media with streams of different length.
- Fix setting of the playback rate before opening sources.
- Add new auto tests for looping.
- Add debug logs.

Pick-to: 6.5
Task-number: QTBUG-112305
Change-Id: Ic9073d77535f5aae19f9ea48d4e745c9f2fa9ea3
Reviewed-by: Lars Knoll <lars@knoll.priv.no>

1 files changed, 5 insertions, 2 deletions

diff --git a/src/plugins/multimedia/ffmpeg/playbackengine/qffmpegstreamdecoder_p.h b/src/plugins/multimedia/ffmpeg/playbackengine/qffmpegstreamdecoder_p.h
index cc12b1e9a..001ec6b90 100644
--- a/src/plugins/multimedia/ffmpeg/playbackengine/qffmpegstreamdecoder_p.h
+++ b/src/plugins/multimedia/ffmpeg/playbackengine/qffmpegstreamdecoder_p.h
@@ -16,6 +16,7 @@
 #include "playbackengine/qffmpegplaybackengineobject_p.h"
 #include "playbackengine/qffmpegframe_p.h"
 #include "playbackengine/qffmpegpacket_p.h"
+#include "playbackengine/qffmpegpositionwithoffset_p.h"
 #include "private/qplatformmediaplayer_p.h"
 
 #include <optional>
@@ -28,7 +29,7 @@ class StreamDecoder : public PlaybackEngineObject
 {
     Q_OBJECT
 public:
-    StreamDecoder(const Codec &codec, qint64 seekPos);
+    StreamDecoder(const Codec &codec, qint64 absSeekPos);
 
     ~StreamDecoder();
 
@@ -64,11 +65,13 @@ private:
 
 private:
     Codec m_codec;
-    qint64 m_seekPos = 0;
+    const qint64 m_absSeekPos = 0;
     const QPlatformMediaPlayer::TrackType m_trackType;
 
     qint32 m_pendingFramesCount = 0;
 
+    LoopOffset m_offset;
+
     QQueue<Packet> m_packets;
 };