public static DataPacket decode(ChannelBuffer buffer) throws IndexOutOfBoundsException {
        if (buffer.readableBytes() < 12) {
            throw new IllegalArgumentException("A RTP packet must be at least 12 octets long");
        }

        // Version, Padding, eXtension, CSRC Count
        DataPacket packet = new DataPacket();
        byte b = buffer.readByte();
        packet.version = RtpVersion.fromByte(b);
        boolean padding = (b & 0x20) > 0; // mask 0010 0000
        boolean extension = (b & 0x10) > 0; // mask 0001 0000
        int contributingSourcesCount = b & 0x0f; // mask 0000 1111

        // Marker, Payload Type
        b = buffer.readByte();
        packet.marker = (b & 0x80) > 0; // mask 0000 0001
        packet.payloadType = (b & 0x7f); // mask 0111 1111

        packet.sequenceNumber = buffer.readUnsignedShort();
        packet.timestamp = buffer.readUnsignedInt();
        packet.ssrc = buffer.readUnsignedInt();

        // Read extension headers & data
        if (extension) {
            packet.extensionHeaderData = buffer.readShort();
            packet.extensionData = new byte[buffer.readUnsignedShort()];
            buffer.readBytes(packet.extensionData);
        }

        // Read CCRC's
        if (contributingSourcesCount > 0) {
            packet.contributingSourceIds = new ArrayList<Long>(contributingSourcesCount);
            for (int i = 0; i < contributingSourcesCount; i++) {
                long contributingSource = buffer.readUnsignedInt();
                packet.contributingSourceIds.add(contributingSource);
            }
        }

        if (!padding) {
            // No padding used, assume remaining data is the packet
            byte[] remainingBytes = new byte[buffer.readableBytes()];
            buffer.readBytes(remainingBytes);
            packet.setData(remainingBytes);
        } else {
            // Padding bit was set, so last byte contains the number of padding octets that should be discarded.
            short lastByte = buffer.getUnsignedByte(buffer.readerIndex() + buffer.readableBytes() - 1);
            byte[] dataBytes = new byte[buffer.readableBytes() - lastByte];
            buffer.readBytes(dataBytes);
            packet.setData(dataBytes);
            // Discard rest of buffer.
            buffer.skipBytes(buffer.readableBytes());
        }

        return packet;
    }

java handler for RTP raw audio packet in:
com.biasedbit.com.efflux.packet.DataPacket

RTP packet handler

Java