/// <summary>
/// Writes captions into a text in WebVTT format.
/// </summary>
/// <param name="captions">Caption blocks to serialize.</param>
/// <param name="writer">Text writer to write into.</param>
/// <remarks>See http://www.w3.org/TR/webvtt1/ for more details.</remarks>
public static Task SerializeAsync(
MediaCaptions captions,
TextWriter writer)
{
return(WebVttSerializer.SerializeAsync(
WebVttSerializer.GetMediaCaptionBlocks(captions),
writer));
}
/// <summary>
/// Utility method to return all parts of media captions are a sequence of blocks.
/// </summary>
/// <param name="captions">Captions to process.</param>
/// <returns>Sequence of blocks.</returns>
private static IEnumerable <BaseBlock> GetMediaCaptionBlocks(
MediaCaptions captions)
{
if (captions != null)
{
if (captions.Styles != null && captions.Styles.Length > 0)
{
foreach (var style in captions.Styles)
{
if (style != null)
{
yield return(style);
}
}
}
if (captions.Regions != null && captions.Regions.Length > 0)
{
foreach (var region in captions.Regions)
{
if (region != null)
{
yield return(region);
}
}
}
if (captions.Cues != null && captions.Cues.Length > 0)
{
bool needSort = false;
Cue previous = null;
foreach (var cue in captions.Cues)
{
if (cue != null)
{
needSort = previous != null && cue.Start < previous.Start;
previous = cue;
}
if (needSort)
{
break;
}
}
if (needSort)
{
var tmp = new List <Cue>(captions.Cues.Length);
foreach (var cue in captions.Cues)
{
if (cue != null)
{
tmp.Add(cue);
}
}
if (tmp.Count > 0)
{
tmp.Sort((c1, c2) => c1.Start < c2.Start
? -1
: (c1.Start > c2.Start ? 1 : c1.End.CompareTo(c2.End)));
foreach (var cue in tmp)
{
yield return(cue);
}
}
}
else
{
foreach (var cue in captions.Cues)
{
yield return(cue);
}
}
}
}
}
/// <summary>
/// Reads WebVTT media captions from a given <see cref="TextReader"/>.
/// </summary>
/// <param name="reader">Text reader to read the captions.</param>
/// <returns>A task that represents the asynchronous read operation.</returns>
public static async Task <MediaCaptions> ReadMediaCaptionsAsync(
TextReader reader)
{
if (reader == null)
{
throw new ArgumentNullException("reader");
}
// Process stream header line
var line = await reader.ReadLineAsync()
.ConfigureAwait(false);
if (string.IsNullOrWhiteSpace(line) ||
line.Length < 6 ||
false == line.StartsWith(Constants.WebVttHeaderToken) ||
line.Length >= 7 && line[6] != '\t' && line[6] != ' ')
{
throw new InvalidDataException("The stream does not start with the correct WebVTT file signature.");
}
var result = new MediaCaptions();
// Process (skip over) optional headers from the stream
while (false == string.IsNullOrEmpty(line))
{
line = await reader.ReadLineAsync()
.ConfigureAwait(false);
}
// Process media caption blocks.
List <RegionDefinition> regions = new List <RegionDefinition>();
List <Style> styles = new List <Style>();
List <Cue> cues = new List <Cue>();
BaseBlock block;
do
{
block = await WebVttParser.ReadBlockAsync(reader)
.ConfigureAwait(false);
RegionDefinition region = block as RegionDefinition;
Style style = block as Style;
Cue cue = block as Cue;
if (cues.Count == 0)
{
if (region != null)
{
regions.Add(region);
}
else if (style != null)
{
styles.Add(style);
}
}
else if (region != null || style != null)
{
throw new InvalidDataException("Region or style blocks cannot be mixed with cue blocks.");
}
if (cue != null)
{
cues.Add(cue);
}
}while (block != null);
if (regions.Count > 0)
{
result.Regions = regions.ToArray();
}
if (styles.Count > 0)
{
result.Styles = styles.ToArray();
}
if (cues.Count > 0)
{
result.Cues = cues.ToArray();
}
return(result);
}
