/**
* Removes the RTX encapsulation from a packet.
*
* @param pkt the packet to remove the RTX encapsulation from.
* @return the original media packet represented by {@code pkt}, or null if we couldn't
* reconstruct the original packet.
*/
private RawPacket deRtx(RawPacket pkt) {
boolean success = false;
if (pkt.getPayloadLength() - pkt.getPaddingSize() < 2) {
// We need at least 2 bytes to read the OSN field.
if (logger.isDebugEnabled()) {
logger.debug("Dropping an incoming RTX packet with padding only: " + pkt);
}
return null;
}
long mediaSsrc = getPrimarySsrc(pkt);
if (mediaSsrc != -1) {
if (rtxAssociatedPayloadType != -1) {
int osn = pkt.getOriginalSequenceNumber();
// Remove the RTX header by moving the RTP header two bytes
// right.
byte[] buf = pkt.getBuffer();
int off = pkt.getOffset();
System.arraycopy(buf, off, buf, off + 2, pkt.getHeaderLength());
pkt.setOffset(off + 2);
pkt.setLength(pkt.getLength() - 2);
pkt.setSSRC((int) mediaSsrc);
pkt.setSequenceNumber(osn);
pkt.setPayloadType(rtxAssociatedPayloadType);
success = true;
} else {
logger.warn(
"RTX packet received, but no APT is defined. Packet "
+ "SSRC "
+ pkt.getSSRCAsLong()
+ ", associated media"
+ " SSRC "
+ mediaSsrc);
}
}
// If we failed to handle the RTX packet, drop it.
return success ? pkt : null;
}
/**
* Encapsulates {@code pkt} in the RTX format, using {@code rtxSsrc} as its SSRC, and transmits it
* to {@link #channel} by injecting it in the {@code MediaStream}.
*
* @param pkt the packet to transmit.
* @param rtxSsrc the SSRC for the RTX stream.
* @param after the {@code TransformEngine} in the chain of {@code TransformEngine}s of the
* associated {@code MediaStream} after which the injection of {@code pkt} is to begin
* @return {@code true} if the packet was successfully retransmitted, {@code false} otherwise.
*/
private boolean encapsulateInRtxAndTransmit(RawPacket pkt, long rtxSsrc, TransformEngine after) {
byte[] buf = pkt.getBuffer();
int len = pkt.getLength();
int off = pkt.getOffset();
byte[] newBuf = new byte[len + 2];
RawPacket rtxPkt = new RawPacket(newBuf, 0, len + 2);
int osn = pkt.getSequenceNumber();
int headerLength = pkt.getHeaderLength();
int payloadLength = pkt.getPayloadLength();
// Copy the header.
System.arraycopy(buf, off, newBuf, 0, headerLength);
// Set the OSN field.
newBuf[headerLength] = (byte) ((osn >> 8) & 0xff);
newBuf[headerLength + 1] = (byte) (osn & 0xff);
// Copy the payload.
System.arraycopy(buf, off + headerLength, newBuf, headerLength + 2, payloadLength);
MediaStream mediaStream = channel.getStream();
if (mediaStream != null) {
rtxPkt.setSSRC((int) rtxSsrc);
rtxPkt.setPayloadType(rtxPayloadType);
// Only call getNextRtxSequenceNumber() when we're sure we're going
// to transmit a packet, because it consumes a sequence number.
rtxPkt.setSequenceNumber(getNextRtxSequenceNumber(rtxSsrc));
try {
mediaStream.injectPacket(rtxPkt, /* data */ true, after);
} catch (TransmissionFailedException tfe) {
logger.warn("Failed to transmit an RTX packet.");
return false;
}
}
return true;
}
/**
* Creates a {@code RawPacket} which represents the original packet encapsulated in {@code pkt}
* using the RTX format.
*
* @param pkt the packet from which to extract a media packet.
* @return the extracted media packet.
*/
private RawPacket createMediaPacket(RawPacket pkt) {
RawPacket mediaPacket = null;
long rtxSsrc = pkt.getSSRC() & 0xffffffffL;
// We need to know the SSRC paired with rtxSsrc *as seen by the
// receiver (i.e. this.channel)*. However, we only store SSRCs
// that endpoints *send* with.
// We therefore assume that SSRC re-writing has not introduced any
// new SSRCs and therefor the FID mappings known to the senders
// also apply to receivers.
RtpChannel sourceChannel = channel.getContent().findChannelByFidSsrc(rtxSsrc);
if (sourceChannel != null) {
long mediaSsrc = sourceChannel.getFidPairedSsrc(rtxSsrc);
if (mediaSsrc != -1) {
byte apt = sourceChannel.getRtxAssociatedPayloadType();
if (apt != -1) {
mediaPacket = new RawPacket(pkt.getBuffer().clone(), pkt.getOffset(), pkt.getLength());
// Remove the RTX header by moving the RTP header two bytes
// right.
byte[] buf = mediaPacket.getBuffer();
int off = mediaPacket.getOffset();
System.arraycopy(buf, off, buf, off + 2, mediaPacket.getHeaderLength());
mediaPacket.setOffset(off + 2);
mediaPacket.setLength(pkt.getLength() - 2);
mediaPacket.setSSRC((int) mediaSsrc);
mediaPacket.setSequenceNumber(pkt.getOriginalSequenceNumber());
mediaPacket.setPayloadType(apt);
}
}
}
return mediaPacket;
}