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import fractions
import logging
import math
from itertools import tee
from struct import pack, unpack_from
from typing import Iterator, List, Optional, Sequence, Tuple, Type, TypeVar, cast
import av
from av.frame import Frame
from av.packet import Packet
from av.video.codeccontext import VideoCodecContext
from ..jitterbuffer import JitterFrame
from ..mediastreams import VIDEO_TIME_BASE, convert_timebase
from .base import Decoder, Encoder
logger = logging.getLogger(__name__)
DEFAULT_BITRATE = 1000000 # 1 Mbps
MIN_BITRATE = 500000 # 500 kbps
MAX_BITRATE = 3000000 # 3 Mbps
MAX_FRAME_RATE = 30
PACKET_MAX = 1300
NAL_TYPE_FU_A = 28
NAL_TYPE_STAP_A = 24
NAL_HEADER_SIZE = 1
FU_A_HEADER_SIZE = 2
LENGTH_FIELD_SIZE = 2
STAP_A_HEADER_SIZE = NAL_HEADER_SIZE + LENGTH_FIELD_SIZE
DESCRIPTOR_T = TypeVar("DESCRIPTOR_T", bound="H264PayloadDescriptor")
T = TypeVar("T")
def pairwise(iterable: Sequence[T]) -> Iterator[Tuple[T, T]]:
a, b = tee(iterable)
next(b, None)
return zip(a, b)
class H264PayloadDescriptor:
def __init__(self, first_fragment):
self.first_fragment = first_fragment
def __repr__(self):
return f"H264PayloadDescriptor(FF={self.first_fragment})"
@classmethod
def parse(cls: Type[DESCRIPTOR_T], data: bytes) -> Tuple[DESCRIPTOR_T, bytes]:
output = bytes()
# NAL unit header
if len(data) < 2:
raise ValueError("NAL unit is too short")
nal_type = data[0] & 0x1F
f_nri = data[0] & (0x80 | 0x60)
pos = NAL_HEADER_SIZE
if nal_type in range(1, 24):
# single NAL unit
output = bytes([0, 0, 0, 1]) + data
obj = cls(first_fragment=True)
elif nal_type == NAL_TYPE_FU_A:
# fragmentation unit
original_nal_type = data[pos] & 0x1F
first_fragment = bool(data[pos] & 0x80)
pos += 1
if first_fragment:
original_nal_header = bytes([f_nri | original_nal_type])
output += bytes([0, 0, 0, 1])
output += original_nal_header
output += data[pos:]
obj = cls(first_fragment=first_fragment)
elif nal_type == NAL_TYPE_STAP_A:
# single time aggregation packet
offsets = []
while pos < len(data):
if len(data) < pos + LENGTH_FIELD_SIZE:
raise ValueError("STAP-A length field is truncated")
nalu_size = unpack_from("!H", data, pos)[0]
pos += LENGTH_FIELD_SIZE
offsets.append(pos)
pos += nalu_size
if len(data) < pos:
raise ValueError("STAP-A data is truncated")
offsets.append(len(data) + LENGTH_FIELD_SIZE)
for start, end in pairwise(offsets):
end -= LENGTH_FIELD_SIZE
output += bytes([0, 0, 0, 1])
output += data[start:end]
obj = cls(first_fragment=True)
else:
raise ValueError(f"NAL unit type {nal_type} is not supported")
return obj, output
class H264Decoder(Decoder):
def __init__(self) -> None:
self.codec = cast(VideoCodecContext, av.CodecContext.create("h264", "r"))
def decode(self, encoded_frame: JitterFrame) -> List[Frame]:
try:
packet = av.Packet(encoded_frame.data)
packet.pts = encoded_frame.timestamp
packet.time_base = VIDEO_TIME_BASE
return cast(List[Frame], self.codec.decode(packet))
except av.AVError as e:
logger.warning(
"H264Decoder() failed to decode, skipping package: " + str(e)
)
return []
def create_encoder_context(
codec_name: str, width: int, height: int, bitrate: int
) -> Tuple[VideoCodecContext, bool]:
codec = cast(VideoCodecContext, av.CodecContext.create(codec_name, "w"))
codec.width = width
codec.height = height
codec.bit_rate = bitrate
codec.pix_fmt = "yuv420p"
codec.framerate = fractions.Fraction(MAX_FRAME_RATE, 1)
codec.time_base = fractions.Fraction(1, MAX_FRAME_RATE)
codec.options = {
"profile": "baseline",
"level": "31",
"tune": "zerolatency", # does nothing using h264_omx
}
codec.open()
return codec, codec_name == "h264_omx"
class H264Encoder(Encoder):
def __init__(self) -> None:
self.buffer_data = b""
self.buffer_pts: Optional[int] = None
self.codec: Optional[VideoCodecContext] = None
self.codec_buffering = False
self.__target_bitrate = DEFAULT_BITRATE
@staticmethod
def _packetize_fu_a(data: bytes) -> List[bytes]:
available_size = PACKET_MAX - FU_A_HEADER_SIZE
payload_size = len(data) - NAL_HEADER_SIZE
num_packets = math.ceil(payload_size / available_size)
num_larger_packets = payload_size % num_packets
package_size = payload_size // num_packets
f_nri = data[0] & (0x80 | 0x60) # fni of original header
nal = data[0] & 0x1F
fu_indicator = f_nri | NAL_TYPE_FU_A
fu_header_end = bytes([fu_indicator, nal | 0x40])
fu_header_middle = bytes([fu_indicator, nal])
fu_header_start = bytes([fu_indicator, nal | 0x80])
fu_header = fu_header_start
packages = []
offset = NAL_HEADER_SIZE
while offset < len(data):
if num_larger_packets > 0:
num_larger_packets -= 1
payload = data[offset : offset + package_size + 1]
offset += package_size + 1
else:
payload = data[offset : offset + package_size]
offset += package_size
if offset == len(data):
fu_header = fu_header_end
packages.append(fu_header + payload)
fu_header = fu_header_middle
assert offset == len(data), "incorrect fragment data"
return packages
@staticmethod
def _packetize_stap_a(
data: bytes, packages_iterator: Iterator[bytes]
) -> Tuple[bytes, bytes]:
counter = 0
available_size = PACKET_MAX - STAP_A_HEADER_SIZE
stap_header = NAL_TYPE_STAP_A | (data[0] & 0xE0)
payload = bytes()
try:
nalu = data # with header
while len(nalu) <= available_size and counter < 9:
stap_header |= nalu[0] & 0x80
nri = nalu[0] & 0x60
if stap_header & 0x60 < nri:
stap_header = stap_header & 0x9F | nri
available_size -= LENGTH_FIELD_SIZE + len(nalu)
counter += 1
payload += pack("!H", len(nalu)) + nalu
nalu = next(packages_iterator)
if counter == 0:
nalu = next(packages_iterator)
except StopIteration:
nalu = None
if counter <= 1:
return data, nalu
else:
return bytes([stap_header]) + payload, nalu
@staticmethod
def _split_bitstream(buf: bytes) -> Iterator[bytes]:
# Translated from: https://github.com/aizvorski/h264bitstream/blob/master/h264_nal.c#L134
i = 0
while True:
# Find the start of the NAL unit.
#
# NAL Units start with the 3-byte start code 0x000001 or
# the 4-byte start code 0x00000001.
i = buf.find(b"\x00\x00\x01", i)
if i == -1:
return
# Jump past the start code
i += 3
nal_start = i
# Find the end of the NAL unit (end of buffer OR next start code)
i = buf.find(b"\x00\x00\x01", i)
if i == -1:
yield buf[nal_start : len(buf)]
return
elif buf[i - 1] == 0:
# 4-byte start code case, jump back one byte
yield buf[nal_start : i - 1]
else:
yield buf[nal_start:i]
@classmethod
def _packetize(cls, packages: Iterator[bytes]) -> List[bytes]:
packetized_packages = []
packages_iterator = iter(packages)
package = next(packages_iterator, None)
while package is not None:
if len(package) > PACKET_MAX:
packetized_packages.extend(cls._packetize_fu_a(package))
package = next(packages_iterator, None)
else:
packetized, package = cls._packetize_stap_a(package, packages_iterator)
packetized_packages.append(packetized)
return packetized_packages
def _encode_frame(
self, frame: av.VideoFrame, force_keyframe: bool
) -> Iterator[bytes]:
if self.codec and (
frame.width != self.codec.width
or frame.height != self.codec.height
# we only adjust bitrate if it changes by over 10%
or abs(self.target_bitrate - self.codec.bit_rate) / self.codec.bit_rate
> 0.1
):
self.buffer_data = b""
self.buffer_pts = None
self.codec = None
if force_keyframe:
# force a complete image
frame.pict_type = av.video.frame.PictureType.I
else:
# reset the picture type, otherwise no B-frames are produced
frame.pict_type = av.video.frame.PictureType.NONE
if self.codec is None:
try:
self.codec, self.codec_buffering = create_encoder_context(
"h264_omx", frame.width, frame.height, bitrate=self.target_bitrate
)
except Exception:
self.codec, self.codec_buffering = create_encoder_context(
"libx264",
frame.width,
frame.height,
bitrate=self.target_bitrate,
)
data_to_send = b""
for package in self.codec.encode(frame):
package_bytes = bytes(package)
if self.codec_buffering:
# delay sending to ensure we accumulate all packages
# for a given PTS
if package.pts == self.buffer_pts:
self.buffer_data += package_bytes
else:
data_to_send += self.buffer_data
self.buffer_data = package_bytes
self.buffer_pts = package.pts
else:
data_to_send += package_bytes
if data_to_send:
yield from self._split_bitstream(data_to_send)
def encode(
self, frame: Frame, force_keyframe: bool = False
) -> Tuple[List[bytes], int]:
assert isinstance(frame, av.VideoFrame)
packages = self._encode_frame(frame, force_keyframe)
timestamp = convert_timebase(frame.pts, frame.time_base, VIDEO_TIME_BASE)
return self._packetize(packages), timestamp
def pack(self, packet: Packet) -> Tuple[List[bytes], int]:
assert isinstance(packet, av.Packet)
packages = self._split_bitstream(bytes(packet))
timestamp = convert_timebase(packet.pts, packet.time_base, VIDEO_TIME_BASE)
return self._packetize(packages), timestamp
@property
def target_bitrate(self) -> int:
"""
Target bitrate in bits per second.
"""
return self.__target_bitrate
@target_bitrate.setter
def target_bitrate(self, bitrate: int) -> None:
bitrate = max(MIN_BITRATE, min(bitrate, MAX_BITRATE))
self.__target_bitrate = bitrate
def h264_depayload(payload: bytes) -> bytes:
descriptor, data = H264PayloadDescriptor.parse(payload)
return data
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