Provide better seeking and position display for some videos.

Specifically, there are examples of poorly-encoded avi files that
report a video frame rate of 30fps but the video stream is actually
24fps.  Because frame intervals are actually encoded as 30fps, every
4th frame has to be repeated.  Without an adjustment to framesPlayed,
translations between MythPlayer's frame-based seeking/display and
ffmpeg's timecode-based seeking drift out of sync.

Note: Similar adjustments may be necessary if frames have to be
dropped due to a frame rate mismatch.

Refs #11415.

mythtv/libs/libmythtv/mythplayer.cpp

@@ -165,6 +165,7 @@ MythPlayer::MythPlayer(PlayerFlags flags)
       fftime(0),
       // Playback misc.
       videobuf_retries(0),          framesPlayed(0),
+      framesPlayedExtra(0),
       totalFrames(0),               totalLength(0),
       totalDuration(0),
       rewindtime(0),
@@ -376,7 +377,7 @@ bool MythPlayer::Pause(void)
         if (FlagIsSet(kVideoIsNull) && decoder)
             decoder->UpdateFramesPlayed();
         else if (videoOutput && !FlagIsSet(kVideoIsNull))
-            framesPlayed = videoOutput->GetFramesPlayed();
+            framesPlayed = videoOutput->GetFramesPlayed() + framesPlayedExtra;
     }
     pauseLock.unlock();
     return already_paused;
@@ -1025,6 +1026,7 @@ int MythPlayer::OpenFile(uint retries)
 void MythPlayer::SetFramesPlayed(uint64_t played)
 {
     framesPlayed = played;
+    framesPlayedExtra = 0;
     if (videoOutput)
         videoOutput->SetFramesPlayed(played);
 }
@@ -1995,6 +1997,13 @@ void MythPlayer::AVSync(VideoFrame *buffer, bool limit_delay)
                     LOG(VB_PLAYBACK | VB_TIMESTAMP, LOG_INFO, LOC +
                         QString("A/V delay %1").arg(delta));
                     avsync_adjustment += frame_interval;
+                    // If we're duplicating a frame, it may be because
+                    // the container frame rate doesn't match the
+                    // stream frame rate.  In this case, we increment
+                    // the fake frame counter so that avformat
+                    // timestamp-based seeking will work.
+                    if (!decoder->HasPositionMap())
+                        ++framesPlayedExtra;
                 }
             }
             prevtc = timecode;
@@ -2402,7 +2411,7 @@ bool MythPlayer::VideoLoop(void)
     else if (decoder && decoder->GetEof() != kEofStateNone)
         ++framesPlayed;
     else
-        framesPlayed = videoOutput->GetFramesPlayed();
+        framesPlayed = videoOutput->GetFramesPlayed() + framesPlayedExtra;
     return !IsErrored();
 }
 
@@ -2488,7 +2497,7 @@ void MythPlayer::ResetPlaying(bool resetframes)
     ClearAfterSeek();
     ffrew_skip = 1;
     if (resetframes)
-        framesPlayed = 0;
+        framesPlayed = framesPlayedExtra = 0;
     if (decoder)
     {
         decoder->Reset(true, true, true);
@@ -2761,6 +2770,7 @@ bool MythPlayer::StartPlaying(void)
     }
 
     framesPlayed = 0;
+    framesPlayedExtra = 0;
     rewindtime = fftime = 0;
     next_play_speed = audio.GetStretchFactor();
     jumpchapter = 0;
@@ -4541,6 +4551,7 @@ void MythPlayer::InitForTranscode(bool copyaudio, bool copyvideo)
     }
 
     framesPlayed = 0;
+    framesPlayedExtra = 0;
     ClearAfterSeek();
 
     if (copyvideo && decoder)

mythtv/libs/libmythtv/mythplayer.h

@@ -681,6 +681,9 @@ class MTV_PUBLIC MythPlayer
     /// How often we have tried to wait for a video output buffer and failed
     int       videobuf_retries;
     uint64_t  framesPlayed;
+    // "Fake" frame counter for when the container frame rate doesn't
+    // match the stream frame rate.
+    uint64_t  framesPlayedExtra;
     uint64_t  totalFrames;
     long long totalLength;
     int64_t   totalDuration;