internal void PreparePacket(ReadOnlySpan <byte> pcm, ref Memory <byte> target)
{
var audioFormat = AudioFormat;
var packetArray = ArrayPool <byte> .Shared.Rent(Rtp.CalculatePacketSize(audioFormat.SampleCountToSampleSize(audioFormat.CalculateMaximumFrameSize()), SelectedEncryptionMode));
var packet = packetArray.AsSpan();
Rtp.EncodeHeader(Sequence, Timestamp, SSRC, packet);
var opus = packet.Slice(Rtp.HeaderSize, pcm.Length);
Opus.Encode(pcm, ref opus);
Sequence++;
Timestamp += (uint)audioFormat.CalculateFrameSize(audioFormat.CalculateSampleDuration(pcm.Length));
Span <byte> nonce = new byte[Sodium.NonceSize];
switch (SelectedEncryptionMode)
{
case EncryptionMode.XSalsa20_Poly1305:
Sodium.GenerateNonce(packet.Slice(0, Rtp.HeaderSize), nonce);
break;
case EncryptionMode.XSalsa20_Poly1305_Suffix:
Sodium.GenerateNonce(nonce);
break;
case EncryptionMode.XSalsa20_Poly1305_Lite:
Sodium.GenerateNonce(Nonce++, nonce);
break;
default:
ArrayPool <byte> .Shared.Return(packetArray);
throw new Exception("Unsupported encryption mode.");
}
Span <byte> encrypted = new byte[Sodium.CalculateTargetSize(opus)];
Sodium.Encrypt(opus, encrypted, nonce);
encrypted.CopyTo(packet.Slice(Rtp.HeaderSize));
packet = packet.Slice(0, Rtp.CalculatePacketSize(encrypted.Length, SelectedEncryptionMode));
Sodium.AppendNonce(nonce, packet, SelectedEncryptionMode);
target = target.Slice(0, packet.Length);
packet.CopyTo(target.Span);
ArrayPool <byte> .Shared.Return(packetArray);
}