From 2b14e9044e2d93ea320146b27e09aaa1db0a9684 Mon Sep 17 00:00:00 2001
From: Isaac Connor <isaac@zoneminder.com>
Date: Thu, 26 Feb 2026 13:16:07 -0500
Subject: [PATCH] fix: improve montage review playback smoothness and fix video
 seek overshoot

Fix FFmpeg initial seek overshooting to a future keyframe when the
requested timestamp falls between keyframes. After the initial
AVSEEK_FLAG_FRAME seek, detect if the returned frame is past the
target and re-seek backward to get the correct keyframe before it.

On the JS side, preserve fractional seconds throughout the playback
pipeline: remove Math.floor() truncation in mmove() and setSpeed(),
and use parseFloat instead of parseInt for currentTimeSecs
initialization. Reduce initial display interval from 1000ms to 100ms
for ~10fps refresh rate during review playback.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
---
 src/zm_ffmpeg_input.cpp                         | 12 ++++++++++++
 web/skins/classic/views/js/montagereview.js     |  7 +++----
 web/skins/classic/views/js/montagereview.js.php |  4 ++--
 web/skins/classic/views/montagereview.php       |  2 +-
 4 files changed, 18 insertions(+), 7 deletions(-)

diff --git a/src/zm_ffmpeg_input.cpp b/src/zm_ffmpeg_input.cpp
index d0b469c89..130e54d32 100644
--- a/src/zm_ffmpeg_input.cpp
+++ b/src/zm_ffmpeg_input.cpp
@@ -283,6 +283,18 @@ AVFrame *FFmpeg_Input::get_frame(int stream_id, double at) {
       Warning("Unable to get frame.");
       return nullptr;
     }
+
+    // If the initial seek landed past the target (on a future keyframe),
+    // re-seek backward to get the keyframe before the target instead.
+    if (frame->pts > seek_target) {
+      Debug(1, "Initial seek overshot: frame pts %" PRId64 " > seek_target %" PRId64 ", seeking backward",
+            frame->pts, seek_target);
+      ret = av_seek_frame(input_format_context, stream_id, seek_target,
+                          AVSEEK_FLAG_BACKWARD);
+      if (ret >= 0) {
+        get_frame(stream_id);
+      }
+    }
   }  // end if ! frame
 
   if (
diff --git a/web/skins/classic/views/js/montagereview.js b/web/skins/classic/views/js/montagereview.js
index 0bb4f6412..fc6a80bdb 100644
--- a/web/skins/classic/views/js/montagereview.js
+++ b/web/skins/classic/views/js/montagereview.js
@@ -825,8 +825,8 @@ function mmove(event) {
   if ( mouseisdown ) {
     // only do anything if the mouse is depressed while on the sheet
     const relx = event.target.relMouseCoords(event).x;
-    const sec = Math.floor(minTimeSecs + rangeTimeSecs / event.target.width * relx);
-    if (parseInt(sec)) outputUpdate(sec);
+    const sec = minTimeSecs + rangeTimeSecs / event.target.width * relx;
+    if (sec) outputUpdate(sec);
   }
 }
 
@@ -890,7 +890,7 @@ function setSpeed(speed_index) {
   }
   currentSpeed = parseFloat(speeds[speed_index]);
   speedIndex = speed_index;
-  playSecsPerInterval = Math.floor( 1000 * currentSpeed * currentDisplayInterval ) / 1000000;
+  playSecsPerInterval = currentSpeed * currentDisplayInterval / 1000;
   setCookie('speed', speedIndex);
   showSpeed(speed_index);
   timerFire();
@@ -1475,7 +1475,6 @@ function loadFrames(zm_events) {
                 if (last_frame && (frame.EventId != last_frame.EventId)) {
                   last_frame = null;
                 }
-                //console.log(date, frame.TimeStamp, frame.Delta, frame.TimeStampSecs);
                 if (last_frame) {
                   frame.PrevFrameId = last_frame.Id;
                   last_frame.NextFrameId = frame.Id;
diff --git a/web/skins/classic/views/js/montagereview.js.php b/web/skins/classic/views/js/montagereview.js.php
index a62ae54d8..601f645f4 100644
--- a/web/skins/classic/views/js/montagereview.js.php
+++ b/web/skins/classic/views/js/montagereview.js.php
@@ -177,9 +177,9 @@ var maxTime='$maxTime';
 ";
 echo 'var rangeTimeSecs='.($maxTimeSecs - $minTimeSecs + 1).";\n";
 if ( isset($defaultCurrentTimeSecs) ) {
-  echo 'var currentTimeSecs=parseInt('.$defaultCurrentTimeSecs.");\n";
+  echo 'var currentTimeSecs=parseFloat('.$defaultCurrentTimeSecs.");\n";
 } else {
-  echo 'var currentTimeSecs=parseInt('.$minTimeSecs.");\n";
+  echo 'var currentTimeSecs=parseFloat('.$minTimeSecs.");\n";
 }
 
 echo 'var speeds=[';
diff --git a/web/skins/classic/views/montagereview.php b/web/skins/classic/views/montagereview.php
index 9fdaa658a..db9b91baf 100644
--- a/web/skins/classic/views/montagereview.php
+++ b/web/skins/classic/views/montagereview.php
@@ -243,7 +243,7 @@ for ( $i = 0; $i < count($speeds); $i++ ) {
   }
 }
 
-$initialDisplayInterval = 1000;
+$initialDisplayInterval = 100;
 if (isset($_REQUEST['displayinterval']))
   $initialDisplayInterval = validCardinal($_REQUEST['displayinterval']);