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//
// SDLRTPH264Packetizer.m
// SmartDeviceLink-iOS
//
// Created by Sho Amano on 4/11/17.
// Copyright © 2017 Xevo Inc. All rights reserved.
//
/*
* Note for testing.
* The RTP stream generated by this packetizer can be tested with GStreamer (1.4 or later).
* Assuming that "VideoStreamPort" is configured as 5050 in smartDeviceLink.ini, here is the
* GStreamer pipeline that receives the stream, decode it and render it:
*
* $ gst-launch-1.0 souphttpsrc location=http://127.0.0.1:5050 ! "application/x-rtp-stream" ! rtpstreamdepay ! "application/x-rtp,media=(string)video,clock-rate=90000,encoding-name=(string)H264" ! rtph264depay ! "video/x-h264, stream-format=(string)avc, alignment=(string)au" ! avdec_h264 ! autovideosink sync=false
*/
#import <Foundation/Foundation.h>
#import "SDLRTPH264Packetizer.h"
#import "SDLLogMacros.h"
const NSUInteger FRAME_LENGTH_LEN = 2;
const NSUInteger MAX_RTP_PACKET_SIZE = 65535; // because length field is two bytes (RFC 4571)
const NSUInteger RTP_HEADER_LEN = 12;
const UInt8 DEFAULT_PAYLOAD_TYPE = 96;
const NSUInteger FU_INDICATOR_LEN = 1;
const NSUInteger FU_HEADER_LEN = 1;
const UInt8 TYPE_FU_A = 0x1C;
const NSUInteger CLOCK_RATE = 90000; // we use 90 kHz clock rate ([5.1] in RFC 6184)
// write 2-byte value in network byte order
static inline void writeShortInNBO(UInt8 *p, UInt16 value) {
p[0] = (value >> 8) & 0xFF;
p[1] = value & 0xFF;
}
// write 4-byte value in network byte order
static inline void writeLongInNBO(UInt8 *p, UInt32 value) {
p[0] = (value >> 24) & 0xFF;
p[1] = (value >> 16) & 0xFF;
p[2] = (value >> 8) & 0xFF;
p[3] = value & 0xFF;
}
NS_ASSUME_NONNULL_BEGIN
@interface SDLRTPH264Packetizer ()
@property (assign, nonatomic) UInt32 initialTimestamp;
@property (assign, nonatomic) UInt16 sequenceNum;
@end
@implementation SDLRTPH264Packetizer
- (instancetype)init {
if (self = [super init]) {
_payloadType = DEFAULT_PAYLOAD_TYPE;
// initial value of the sequence number and timestamp should be random ([5.1] in RFC3550)
_initialTimestamp = arc4random_uniform(UINT32_MAX);
_sequenceNum = (UInt16)arc4random_uniform(UINT16_MAX);
_ssrc = arc4random_uniform(UINT32_MAX);
}
return self;
}
- (void)setPayloadType:(UInt8)payloadType {
if (payloadType <= 127) {
_payloadType = payloadType;
} else {
_payloadType = DEFAULT_PAYLOAD_TYPE;
}
}
- (nullable NSArray<NSData *> *)createPackets:(NSArray<NSData *> *)nalUnits
presentationTimestamp:(double)presentationTimestamp {
NSMutableArray *rtpFrames = [NSMutableArray array];
NSUInteger nalUnitsCount = [nalUnits count];
for (NSUInteger i = 0; i < nalUnitsCount; i++) {
NSData *nalUnit = nalUnits[i];
NSUInteger nalUnitLength = [nalUnit length];
BOOL isLast = (i + 1) == nalUnitsCount;
if (RTP_HEADER_LEN + nalUnitLength > MAX_RTP_PACKET_SIZE) {
// Split into multiple Fragmentation Units ([5.8] in RFC 6184)
UInt8 firstByte;
[nalUnit getBytes:&firstByte length:1];
BOOL isFirstFragment = YES;
BOOL isLastFragment = NO;
NSUInteger offset = 1; // we have already read the first byte
while (offset < nalUnitLength) {
NSUInteger payloadLength = MAX_RTP_PACKET_SIZE - (RTP_HEADER_LEN + FU_INDICATOR_LEN + FU_HEADER_LEN);
if (nalUnitLength - offset <= payloadLength) {
payloadLength = nalUnitLength - offset;
isLastFragment = YES;
}
NSUInteger packetSize = RTP_HEADER_LEN + FU_INDICATOR_LEN + FU_HEADER_LEN + payloadLength;
NSUInteger frameSize = FRAME_LENGTH_LEN + packetSize;
UInt8 *buffer = malloc(frameSize);
if (buffer == NULL) {
SDLLogE(@"malloc() error");
return nil;
}
UInt8 *p = buffer;
p += [self writeFrameHeader:p packetSize:packetSize];
p += [self writeRTPHeader:p marker:isLast pts:presentationTimestamp];
// FU indicator
*p++ = (firstByte & 0xE0) | TYPE_FU_A;
// FU header
*p++ = (isFirstFragment ? 0x80 : isLastFragment ? 0x40 : 0) | (firstByte & 0x1F);
// FU payload
[nalUnit getBytes:p range:NSMakeRange(offset, payloadLength)];
offset += payloadLength;
NSData *rtpFrame = [NSData dataWithBytesNoCopy:buffer length:frameSize];
[rtpFrames addObject:rtpFrame];
isFirstFragment = NO;
}
} else {
// Use Single NAL Unit Packet ([5.6] in RFC 6184)
NSUInteger packetSize = RTP_HEADER_LEN + nalUnitLength;
NSUInteger frameSize = FRAME_LENGTH_LEN + packetSize;
UInt8 *buffer = malloc(frameSize);
if (buffer == NULL) {
SDLLogE(@"malloc() error");
return nil;
}
UInt8 *p = buffer;
p += [self writeFrameHeader:p packetSize:packetSize];
p += [self writeRTPHeader:p marker:isLast pts:presentationTimestamp];
[nalUnit getBytes:p length:nalUnitLength];
NSData *rtpFrame = [NSData dataWithBytesNoCopy:buffer length:frameSize];
[rtpFrames addObject:rtpFrame];
}
}
return rtpFrames;
}
/**
* Write RTP Frame header (length field) to supplied buffer.
*
* @param p the buffer in which a header is written.
* @param packetSize size of a RTP packet that follows to this frame header.
*
* @return number of bytes written, which is always 2.
*/
- (NSUInteger)writeFrameHeader:(UInt8 *)p packetSize:(NSUInteger)packetSize {
NSAssert(packetSize <= MAX_RTP_PACKET_SIZE, @"RTP packet is too big");
writeShortInNBO(p, (UInt16)packetSize);
return FRAME_LENGTH_LEN;
}
/**
* Write RTP header to supplied buffer.
*
* @param p the buffer in which a header is written.
* @param isLast whether this is the last packet of an access unit.
* @param pts presentation timestamp in seconds.
*
* @return number of bytes written, which is always 12.
*/
- (NSUInteger)writeRTPHeader:(UInt8 *)p marker:(BOOL)isLast pts:(double)pts {
UInt32 ptsIn90kHz = pts * CLOCK_RATE;
// Version = 2, Padding = 0, Extension = 0, CSRC count = 0
p[0] = 0x80;
// Marker = isLast, Payload type = self.payloadType
p[1] = (isLast ? 0x80 : 0) | (self.payloadType & 0x7F);
writeShortInNBO(p + 2, self.sequenceNum);
writeLongInNBO(p + 4, self.initialTimestamp + ptsIn90kHz);
writeLongInNBO(p + 8, self.ssrc);
self.sequenceNum++;
return RTP_HEADER_LEN;
}
@end
NS_ASSUME_NONNULL_END
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