/**
* Retransmits a packet to {@link #channel}. If the destination supports the RTX format, the
* packet will be encapsulated in RTX, otherwise, the packet will be retransmitted as-is.
*
* @param pkt the packet to retransmit.
* @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.
*/
public boolean retransmit(RawPacket pkt, TransformEngine after) {
boolean destinationSupportsRtx = rtxPayloadType != -1;
boolean retransmitPlain;
if (destinationSupportsRtx) {
long rtxSsrc = getRtxSsrc(pkt);
if (rtxSsrc == -1) {
logger.warn(
"Cannot find SSRC for RTX, retransmitting plain. " + "SSRC=" + pkt.getSSRCAsLong());
retransmitPlain = true;
} else {
retransmitPlain = !encapsulateInRtxAndTransmit(pkt, rtxSsrc, after);
}
} else {
retransmitPlain = true;
}
if (retransmitPlain) {
MediaStream mediaStream = channel.getStream();
if (mediaStream != null) {
try {
mediaStream.injectPacket(pkt, /* data */ true, after);
} catch (TransmissionFailedException tfe) {
logger.warn("Failed to retransmit a packet.");
return false;
}
}
}
return true;
}
/**
* Tries to find an SSRC paired with {@code ssrc} in an FID group in one of the channels from
* {@link #channel}'s {@code Content}. Returns -1 on failure.
*
* @param pkt the {@code RawPacket} that holds the RTP packet for which to find a paired SSRC.
* @return An SSRC paired with {@code ssrc} in an FID group, or -1.
*/
private long getRtxSsrc(RawPacket pkt) {
StreamRTPManager receiveRTPManager =
channel.getStream().getRTPTranslator().findStreamRTPManagerByReceiveSSRC(pkt.getSSRC());
MediaStreamTrackReceiver receiver = null;
if (receiveRTPManager != null) {
MediaStream receiveStream = receiveRTPManager.getMediaStream();
if (receiveStream != null) {
receiver = receiveStream.getMediaStreamTrackReceiver();
}
}
if (receiver == null) {
return -1;
}
RTPEncoding encoding = receiver.resolveRTPEncoding(pkt);
if (encoding == null) {
logger.warn(
"encoding_not_found"
+ ",stream_hash="
+ channel.getStream().hashCode()
+ " ssrc="
+ pkt.getSSRCAsLong());
return -1;
}
return encoding.getRTXSSRC();
}
/**
* 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;
}