/// <summary>
/// Parses the given scalabilityMode string according to the rules in webrtc-svc.
/// </summary>
/// <param name="scalabilityMode"></param>
/// <returns></returns>
public static ScalabilityMode Parse(string scalabilityMode)
{
var match = ScalabilityModeRegex.Match(scalabilityMode);
var result = new ScalabilityMode();
if (match.Success)
{
result.SpatialLayers = int.Parse(match.Groups[1].Value);
result.TemporalLayers = int.Parse(match.Groups[2].Value);
result.Ksvc = match.Groups.Count >= 4 && match.Groups[3].Value == "_KEY";
}
else
{
result.SpatialLayers = 1;
result.TemporalLayers = 1;
result.Ksvc = false;
}
return(result);
}
/// <summary>
/// Generate RTP parameters for a specific Consumer.
///
/// It reduces encodings to just one and takes into account given RTP capabilities
/// to reduce codecs, codecs' RTCP feedback and header extensions, and also enables
/// or disabled RTX.
/// </summary>
public static RtpParameters GetConsumerRtpParameters(RtpParameters consumableParams, RtpCapabilities caps)
{
var consumerParams = new RtpParameters
{
Codecs = new List <RtpCodecParameters>(),
HeaderExtensions = new List <RtpHeaderExtensionParameters>(),
Encodings = new List <RtpEncodingParameters>(),
Rtcp = consumableParams.Rtcp
};
foreach (var capCodec in caps.Codecs) // TODO: (alby)注意 null 引用
{
ValidateRtpCodecCapability(capCodec);
}
var consumableCodecs = consumableParams.Codecs.DeepClone <List <RtpCodecParameters> >();
var rtxSupported = false;
foreach (var codec in consumableCodecs)
{
var matchedCapCodec = caps.Codecs
.Where(capCodec => MatchCodecs(capCodec, codec, true))
.FirstOrDefault();
if (matchedCapCodec == null)
{
continue;
}
codec.RtcpFeedback = matchedCapCodec.RtcpFeedback;
consumerParams.Codecs.Add(codec);
if (!rtxSupported && IsRtxMimeType(codec.MimeType))
{
rtxSupported = true;
}
}
// Ensure there is at least one media codec.
if (consumerParams.Codecs.Count == 0 || IsRtxMimeType(consumerParams.Codecs[0].MimeType))
{
throw new Exception("no compatible media codecs");
}
consumerParams.HeaderExtensions = consumableParams.HeaderExtensions
.Where(ext =>
caps.HeaderExtensions
.Any(capExt => capExt.PreferredId == ext.Id && capExt.Uri == ext.Uri)
).ToList();
// Reduce codecs' RTCP feedback. Use Transport-CC if available, REMB otherwise.
if (consumerParams.HeaderExtensions.Any(ext => ext.Uri == "http://www.ietf.org/id/draft-holmer-rmcat-transport-wide-cc-extensions-01"))
{
foreach (var codec in consumerParams.Codecs)
{
codec.RtcpFeedback = codec.RtcpFeedback.Where(fb => fb.Type != "goog-remb").ToArray();
}
}
else if (consumerParams.HeaderExtensions.Any(ext => ext.Uri == "http://www.webrtc.org/experiments/rtp-hdrext/abs-send-time"))
{
foreach (var codec in consumerParams.Codecs)
{
codec.RtcpFeedback = codec.RtcpFeedback.Where(fb => fb.Type != "transport-cc").ToArray();
}
}
else
{
foreach (var codec in consumerParams.Codecs)
{
codec.RtcpFeedback = codec.RtcpFeedback.Where(fb => fb.Type != "transport-cc" && fb.Type != "goog-remb").ToArray();
}
}
var consumerEncoding = new RtpEncodingParameters
{
Ssrc = Utils.GenerateRandomNumber()
};
if (rtxSupported)
{
consumerEncoding.Rtx = new Rtx {
Ssrc = Utils.GenerateRandomNumber()
};
}
// If any in the consumableParams.Encodings has scalabilityMode, process it
// (assume all encodings have the same value).
var encodingWithScalabilityMode = consumableParams.Encodings.Where(encoding => !encoding.ScalabilityMode.IsNullOrWhiteSpace()).FirstOrDefault();
var scalabilityMode = encodingWithScalabilityMode?.ScalabilityMode;
// If there is simulast, mangle spatial layers in scalabilityMode.
if (consumableParams.Encodings.Count > 1) // TODO: (alby)注意 null 引用
{
var scalabilityModeObject = ScalabilityMode.Parse(scalabilityMode); // TODO: (alby)注意 null 引用
scalabilityMode = $"S{ consumableParams.Encodings.Count }T{ scalabilityModeObject.TemporalLayers }";
}
if (!scalabilityMode.IsNullOrWhiteSpace())
{
consumerEncoding.ScalabilityMode = scalabilityMode;
}
// Use the maximum maxBitrate in any encoding and honor it in the Consumer's
// encoding.
var maxEncodingMaxBitrate = consumableParams.Encodings.Max(m => m.MaxBitrate);
if (maxEncodingMaxBitrate.HasValue && maxEncodingMaxBitrate.Value > 0)
{
consumerEncoding.MaxBitrate = maxEncodingMaxBitrate;
}
// Set a single encoding for the Consumer.
consumerParams.Encodings.Add(consumerEncoding);
// Copy verbatim.
consumerParams.Rtcp = consumableParams.Rtcp;
return(consumerParams);
}
