closes issue #216

Unosquare.FFME.Common/Decoding/SubtitleComponent.cs

@@ -20,9 +20,15 @@ internal sealed unsafe class SubtitleComponent : MediaComponent
         internal SubtitleComponent(MediaContainer container, int streamIndex)
             : base(container, streamIndex)
         {
-            // placeholder. Nothing else to change here.
+            // Adjust the offset according to options
+            Delay = container.MediaOptions.SubtitlesDelay;
         }
 
+        /// <summary>
+        /// Gets the amount of time to offset the subtitles by for this component
+        /// </summary>
+        public TimeSpan Delay { get; } = TimeSpan.Zero;
+
         /// <summary>
         /// Converts decoded, raw frame data in the frame source into a a usable frame. <br />
         /// The process includes performing picture, samples or text conversions
@@ -50,6 +56,14 @@ public override MediaBlock MaterializeFrame(MediaFrame input, ref MediaBlock out
             target.Duration = source.Duration;
             target.StreamIndex = input.StreamIndex;
 
+            // Process time offsets
+            if (Delay != TimeSpan.Zero)
+            {
+                target.StartTime = TimeSpan.FromTicks(target.StartTime.Ticks + Delay.Ticks);
+                target.EndTime = TimeSpan.FromTicks(target.EndTime.Ticks + Delay.Ticks);
+                target.Duration = TimeSpan.FromTicks(target.EndTime.Ticks - target.StartTime.Ticks);
+            }
+
             target.OriginalText.Clear();
             if (source.Text.Count > 0)
                 target.OriginalText.AddRange(source.Text);

Unosquare.FFME.Common/Decoding/VideoComponent.cs

@@ -206,10 +206,12 @@ public override MediaBlock MaterializeFrame(MediaFrame input, ref MediaBlock out
                 target.SmtpeTimecode = source.SmtpeTimecode;
             }
 
+            // Fill out other properties
             target.CodedPictureNumber = source.CodedPictureNumber;
             target.StreamIndex = source.StreamIndex;
             target.ClosedCaptions = new ReadOnlyCollection<ClosedCaptions.ClosedCaptionPacket>(source.ClosedCaptions);
 
+            // Process the aspect ratio
             var aspectRatio = source.Pointer->sample_aspect_ratio;
             if (aspectRatio.num == 0 || aspectRatio.den == 0)
             {

Unosquare.FFME.Common/MediaEngine.Workers.cs

@@ -223,6 +223,20 @@ internal void PreloadSubtitles()
                 try
                 {
                     m_PreloadedSubtitles = LoadBlocks(subtitlesUrl, MediaType.Subtitle, this);
+
+                    // Process and adjust subtitle delays if necessary
+                    if (Container.MediaOptions.SubtitlesDelay != TimeSpan.Zero)
+                    {
+                        var delay = Container.MediaOptions.SubtitlesDelay;
+                        for (var i = 0; i < m_PreloadedSubtitles.Count; i++)
+                        {
+                            var target = m_PreloadedSubtitles[i];
+                            target.StartTime = TimeSpan.FromTicks(target.StartTime.Ticks + delay.Ticks);
+                            target.EndTime = TimeSpan.FromTicks(target.EndTime.Ticks + delay.Ticks);
+                            target.Duration = TimeSpan.FromTicks(target.EndTime.Ticks - target.StartTime.Ticks);
+                        }
+                    }
+
                     Container.MediaOptions.IsSubtitleDisabled = true;
                 }
                 catch (MediaContainerException mex)

Unosquare.FFME.Common/Primitives/MediaBlockBuffer.cs

@@ -255,8 +255,11 @@ public MediaBlock Next(MediaBlock current)
         {
             using (Locker.AcquireReaderLock())
             {
-                var currentIndex = PlaybackBlocks.IndexOf(current);
-                if (currentIndex < 0) return null;
+                var currentIndex = current == null && PlaybackBlocks.Count > 0 ?
+                    0 : PlaybackBlocks.IndexOf(current);
+
+                if (currentIndex < 0)
+                    return null;
 
                 if (currentIndex + 1 < PlaybackBlocks.Count)
                     return PlaybackBlocks[currentIndex + 1];

Unosquare.FFME.Common/Shared/MediaOptions.cs

@@ -1,5 +1,6 @@
 namespace Unosquare.FFME.Shared
 {
+    using System;
     using System.Collections.Generic;
 
     /// <summary>
@@ -26,7 +27,13 @@ internal MediaOptions()
         /// This is equivalent to the -codec Main option.
         /// See: https://www.ffmpeg.org/ffmpeg-all.html#Main-options (-codec option)
         /// </summary>
-        public Dictionary<int, string> DecoderCodec { get; } = new Dictionary<int, string>();
+        public Dictionary<int, string> DecoderCodec { get; } = new Dictionary<int, string>(32);
+
+        /// <summary>
+        /// Gets or sets the amount of time to offset the subtitles by
+        /// This is an FFME-only property -- Not a port of ffmpeg.
+        /// </summary>
+        public TimeSpan SubtitlesDelay { get; set; } = TimeSpan.Zero;
 
         /// <summary>
         /// Use Stream's HardwareDevices property to get a list of

Unosquare.FFME.Windows.Sample/MainWindow.MediaEvents.cs

@@ -104,6 +104,9 @@ private void OnMediaInitializing(object sender, MediaInitializingRoutedEventArgs
         /// <param name="e">The <see cref="MediaOpeningRoutedEventArgs"/> instance containing the event data.</param>
         private void OnMediaOpening(object sender, MediaOpeningRoutedEventArgs e)
         {
+            // You can start off by adjusting subtitles delay
+            // e.Options.SubtitlesDelay = TimeSpan.FromSeconds(7); // See issue #216
+
             // Example of automatically side-loading SRT subs
             try
             {
@@ -126,7 +129,9 @@ private void OnMediaOpening(object sender, MediaOpeningRoutedEventArgs e)
             var subtitleStreams = e.Info.Streams.Where(kvp => kvp.Value.CodecType == AVMediaType.AVMEDIA_TYPE_SUBTITLE).Select(kvp => kvp.Value);
             var englishSubtitleStream = subtitleStreams.FirstOrDefault(s => s.Language.StartsWith("en"));
             if (englishSubtitleStream != null)
+            {
                 e.Options.SubtitleStream = englishSubtitleStream;
+            }
 
             var videoStream = e.Options.VideoStream;
             if (videoStream != null)

Unosquare.FFME.Windows/Rendering/SubtitleRenderer.cs

@@ -109,15 +109,25 @@ public void Render(MediaBlock mediaBlock, TimeSpan clockPosition)
                 var subtitleBlock = mediaBlock as SubtitleBlock;
                 if (subtitleBlock == null) return;
 
-                // Save the start and end times. We will need
-                // them in order to make the subtitles disappear
-                StartTime = subtitleBlock.StartTime;
-                EndTime = subtitleBlock.EndTime;
-
                 // Raise the subtitles event and keep track of the text.
-                BlockText = MediaElement.RaiseRenderingSubtitlesEvent(subtitleBlock, clockPosition)
-                    ? string.Empty
-                    : string.Join("\r\n", subtitleBlock.Text);
+                var cancelRender = MediaElement.RaiseRenderingSubtitlesEvent(subtitleBlock, clockPosition);
+
+                if (cancelRender)
+                {
+                    BlockText = string.Empty;
+                    StartTime = null;
+                    EndTime = null;
+                }
+                else
+                {
+                    // Save the block text lines to display
+                    BlockText = string.Join("\r\n", subtitleBlock.Text);
+
+                    // Save the start and end times. We will need
+                    // them in order to make the subtitles disappear
+                    StartTime = subtitleBlock.StartTime;
+                    EndTime = subtitleBlock.EndTime;
+                }
 
                 // Call the selective update method
                 Update(clockPosition);