Make the tool ready to hook a list of fragblobs for vtt file generati…

contracts/ClientManifest.cs

@@ -216,7 +216,9 @@ public class ClientManifest
         {
             foreach (var stream in Streams)
             {
-                if (stream.Type == track.Type)
+                var streamName = stream.Name ?? stream.Type.ToString();
+
+                if (stream.Type == track.Type && streamName == track.TrackName)
                 {
                     for (var i = 0; i < stream.TrackCount; ++i)
                     {

contracts/Manifest.cs

@@ -52,6 +52,8 @@ public Track(StreamType type)
         public bool IsMultiFile => string.IsNullOrEmpty(Path.GetExtension(Source));
 
         public uint TrackID => uint.Parse(Parameters.Single(p => p.Name == "trackID").Value);
+
+        public string TrackName => Parameters.SingleOrDefault(p => p.Name == "trackName")?.Value ?? Type.ToString();
     }
 
     public class VideoTrack : Track

pipes/MultiFileStream.cs

@@ -16,6 +16,7 @@ public class MultiFileStream
         private readonly ILogger _logger;
         private readonly MediaStream _track;
         private readonly string _trackPrefix;
+        private readonly bool _isCloseCaption;
         private readonly StorageEncryptedAssetDecryptionInfo? _decryptInfo;
 
         public MultiFileStream(
@@ -30,6 +31,8 @@ public MultiFileStream(
             (_track, _) = manifest.GetStream(track);
             _trackPrefix = track.Source;
             _decryptInfo = decryptInfo;
+
+            _isCloseCaption = _track.Type == StreamType.Text && _track.SubType == "SUBT";
         }
 
         public async Task DownloadAsync(Stream stream, CancellationToken cancellationToken)
@@ -38,9 +41,16 @@ public async Task DownloadAsync(Stream stream, CancellationToken cancellationTok
             try
             {
                 _logger.LogDebug("Begin downloading track: {name}", _trackPrefix);
-                chunkName = $"{_trackPrefix}/header";
-                var blob = _container.GetBlockBlobClient(chunkName);
-                await DownloadClearBlobContent(blob, stream, cancellationToken);
+
+                BlockBlobClient blob;           
+
+                if (!_isCloseCaption)
+                {
+                    // Header blob is needed only for audio/video cmaf.
+                    chunkName = $"{_trackPrefix}/header";
+                    blob = _container.GetBlockBlobClient(chunkName);
+                    await DownloadClearBlobContent(blob, stream, cancellationToken);
+                }
 
                 // Report progress every 10%.
                 var i = 0;
@@ -133,6 +143,38 @@ private void GenerateCmafFragment(IList<Box> inputBoxes, MP4Writer mp4Writer)
             }
         }
 
+        /// <summary>
+        /// A helper function to generate VTT text for a specific fragblob
+        /// </summary>
+        /// <param name="inputBoxes">A list of boxes for an close caption fragblob.</param>
+        /// <param name="mp4Writer">The writer for the output stream. </param>
+        private void GenerateVttContent(IList<Box> inputBoxes, MP4Writer mp4Writer)
+        {
+            if (inputBoxes.Count != 2)
+            {
+                throw new ArgumentException("A live fragment for close caption must contain two mp4-boxes.", nameof(inputBoxes));
+            }
+
+            var moofBox = inputBoxes[0] as moofBox;
+            var mdatBox = inputBoxes[1] as mdatBox;
+
+            if (moofBox == null || mdatBox == null)
+            {
+                throw new ArgumentException("A live fragment must contain moof box and mdat box.", nameof(inputBoxes));
+            }
+
+            var ttmlText = mdatBox.SampleData;
+
+            byte[] vttText = { 0 };
+
+            // Call API to convert ttmlText to VTT text.
+
+            // Uncomment this line, it was put here to pass the compiler.
+            vttText = ttmlText!;
+
+            mp4Writer.Write(vttText);
+        }
+
         private async Task DownloadClearBlobContent(BlockBlobClient sourceBlob, Stream outputStream, CancellationToken cancellationToken)
         {
             using var tmpStream = new MemoryStream();            
@@ -177,9 +219,16 @@ private async Task DownloadClearBlobContent(BlockBlobClient sourceBlob, Stream o
             }
             else
             {
-                // It is for a fragment generated by a live channel.
-                // Generate cmaf fragment from the input stream.
-                GenerateCmafFragment(boxes, writer);
+                if (_isCloseCaption)
+                {
+                    GenerateVttContent(boxes, writer);
+                }
+                else
+                {
+                    // It is for a fragment generated by a live channel.
+                    // Generate cmaf fragment from the input stream.
+                    GenerateCmafFragment(boxes, writer);
+                }
              }
 
             writer.Flush();

transform/BasePackager.cs

@@ -1,7 +1,6 @@
 using AMSMigrate.Contracts;
 using AMSMigrate.Pipes;
 using Azure.Storage.Blobs.Specialized;
-using FFMpegCore.Pipes;
 using Microsoft.Extensions.Logging;
 using System.Diagnostics;
 
@@ -54,7 +53,23 @@ public BasePackager(AssetDetails assetDetails, TransMuxer transMuxer, ILogger lo
             SelectedTracks = manifest.Tracks.Where(t  => {
                 if (t is TextTrack)
                 {
-                    return !TransmuxedDownload && !t.IsMultiFile && (t.Source.EndsWith(VTT_FILE) || t.Parameters.Any(t => t.Name == TRANSCRIPT_SOURCE));
+                    bool pickThisTextTrack = !TransmuxedDownload && !t.IsMultiFile && (t.Source.EndsWith(VTT_FILE) || t.Parameters.Any(t => t.Name == TRANSCRIPT_SOURCE));
+
+                    if (manifest.IsLiveArchive)
+                    {
+                        pickThisTextTrack = false;
+
+                        if (t.IsMultiFile)
+                        {
+                            // Choose the text track with a list of fragblobs for close captions.
+                            pickThisTextTrack = assetDetails.ClientManifest!.Streams.Any(
+                                                              stream => (stream.Type == StreamType.Text && 
+                                                                         stream.SubType == "SUBT")      &&
+                                                                         stream.Name == t.TrackName);
+                        }                        
+                    }
+
+                    return pickThisTextTrack;
                 }
                 return true;
             }).ToList();
@@ -66,7 +81,14 @@ public BasePackager(AssetDetails assetDetails, TransMuxer transMuxer, ILogger lo
                 string input;
                 if (track is TextTrack)
                 {
-                    input = track.Source.EndsWith(VTT_FILE) ? track.Source : track.Parameters.Single(p => p.Name == TRANSCRIPT_SOURCE).Value;
+                    if (manifest.IsLiveArchive)
+                    {
+                        input = $"{track.Source}{VTT_FILE}";
+                    }
+                    else
+                    {
+                        input = track.Source.EndsWith(VTT_FILE) ? track.Source : track.Parameters.Single(p => p.Name == TRANSCRIPT_SOURCE).Value;
+                    }
                 }
                 else
                 {

transform/FfmpegPackager.cs

@@ -52,7 +52,7 @@ public override async Task<bool> RunAsync(
                 {
                     foreach (var track in SelectedTracks)
                     {
-                        var ext = track.IsMultiFile ? MEDIA_FILE : string.Empty;
+                        var ext = track.IsMultiFile ? (track is TextTrack ? VTT_FILE : MEDIA_FILE) : string.Empty;
                         var index = Inputs.IndexOf($"{track.Source}{ext}");
                         options.SelectStream(0, index, track is VideoTrack ? Channel.Video : Channel.Audio);
                     }

transform/ShakaPackager.cs

@@ -59,7 +59,7 @@ private IEnumerable<string> GetArguments(IList<string> inputs, IList<string> out
 
             List<string> arguments = new(SelectedTracks.Select((t, i) =>
             {
-                var ext = t.IsMultiFile ? MEDIA_FILE : string.Empty;
+                var ext = t.IsMultiFile ? (t is TextTrack ? VTT_FILE : MEDIA_FILE) : string.Empty;
                 var file = $"{t.Source}{ext}";
                 var index = Inputs.IndexOf(file);
                 var multiTrack = TransmuxedDownload && FileToTrackMap[file].Count > 1;