worker.py

"""Provides the worker thread needed for processing streams."""
from __future__ import annotations

from collections import deque
from collections.abc import Iterator, Mapping
from io import BytesIO
import itertools
import logging
from threading import Event
from typing import Any, Callable, cast

import av

from . import redact_credentials
from .const import (
    AUDIO_CODECS,
    MAX_MISSING_DTS,
    MAX_TIMESTAMP_GAP,
    MIN_SEGMENT_DURATION,
    PACKETS_TO_WAIT_FOR_AUDIO,
    SEGMENT_CONTAINER_FORMAT,
    SOURCE_TIMEOUT,
    TARGET_PART_DURATION,
)
from .core import Part, Segment, StreamOutput

_LOGGER = logging.getLogger(__name__)


class SegmentBuffer:
    """Buffer for writing a sequence of packets to the output as a segment."""

    def __init__(
        self, outputs_callback: Callable[[], Mapping[str, StreamOutput]]
    ) -> None:
        """Initialize SegmentBuffer."""
        self._stream_id: int = 0
        self._outputs_callback: Callable[
            [], Mapping[str, StreamOutput]
        ] = outputs_callback
        # sequence gets incremented before the first segment so the first segment
        # has a sequence number of 0.
        self._sequence = -1
        self._segment_start_dts: int = cast(int, None)
        self._memory_file: BytesIO = cast(BytesIO, None)
        self._av_output: av.container.OutputContainer = None
        self._input_video_stream: av.video.VideoStream = None
        self._input_audio_stream: av.audio.stream.AudioStream | None = None
        self._output_video_stream: av.video.VideoStream = None
        self._output_audio_stream: av.audio.stream.AudioStream | None = None
        self._segment: Segment | None = None
        # the following 3 member variables are used for Part formation
        self._memory_file_pos: int = cast(int, None)
        self._part_start_dts: int = cast(int, None)
        self._part_has_keyframe = False

    @staticmethod
    def make_new_av(
        memory_file: BytesIO, sequence: int, input_vstream: av.video.VideoStream
    ) -> av.container.OutputContainer:
        """Make a new av OutputContainer."""
        return av.open(
            memory_file,
            mode="w",
            format=SEGMENT_CONTAINER_FORMAT,
            container_options={
                # Removed skip_sidx - see https://github.com/home-assistant/core/pull/39970
                # "cmaf" flag replaces several of the movflags used, but too recent to use for now
                "movflags": "empty_moov+default_base_moof+frag_discont+negative_cts_offsets+skip_trailer",
                # Sometimes the first segment begins with negative timestamps, and this setting just
                # adjusts the timestamps in the output from that segment to start from 0. Helps from
                # having to make some adjustments in test_durations
                "avoid_negative_ts": "make_non_negative",
                "fragment_index": str(sequence + 1),
                "video_track_timescale": str(int(1 / input_vstream.time_base)),
                # Create a fragments every TARGET_PART_DURATION. The data from each fragment is stored in
                # a "Part" that can be combined with the data from all the other "Part"s, plus an init
                # section, to reconstitute the data in a "Segment".
                "frag_duration": str(int(TARGET_PART_DURATION * 1e6)),
            },
        )

    def set_streams(
        self,
        video_stream: av.video.VideoStream,
        audio_stream: Any,
        # no type hint for audio_stream until https://github.com/PyAV-Org/PyAV/pull/775 is merged
    ) -> None:
        """Initialize output buffer with streams from container."""
        self._input_video_stream = video_stream
        self._input_audio_stream = audio_stream

    def reset(self, video_dts: int) -> None:
        """Initialize a new stream segment."""
        # Keep track of the number of segments we've processed
        self._sequence += 1
        self._segment_start_dts = video_dts
        self._segment = None
        self._memory_file = BytesIO()
        self._memory_file_pos = 0
        self._av_output = self.make_new_av(
            memory_file=self._memory_file,
            sequence=self._sequence,
            input_vstream=self._input_video_stream,
        )
        self._output_video_stream = self._av_output.add_stream(
            template=self._input_video_stream
        )
        # Check if audio is requested
        self._output_audio_stream = None
        if self._input_audio_stream and self._input_audio_stream.name in AUDIO_CODECS:
            self._output_audio_stream = self._av_output.add_stream(
                template=self._input_audio_stream
            )

    def mux_packet(self, packet: av.Packet) -> None:
        """Mux a packet to the appropriate output stream."""

        # Check for end of segment
        if packet.stream == self._input_video_stream:

            if (
                packet.is_keyframe
                and (packet.dts - self._segment_start_dts) * packet.time_base
                >= MIN_SEGMENT_DURATION
            ):
                # Flush segment (also flushes the stub part segment)
                self.flush(packet, last_part=True)
                # Reinitialize
                self.reset(packet.dts)

            # Mux the packet
            packet.stream = self._output_video_stream
            self._av_output.mux(packet)
            self.check_flush_part(packet)
            self._part_has_keyframe |= packet.is_keyframe

        elif packet.stream == self._input_audio_stream:
            packet.stream = self._output_audio_stream
            self._av_output.mux(packet)

    def check_flush_part(self, packet: av.Packet) -> None:
        """Check for and mark a part segment boundary and record its duration."""
        if self._memory_file_pos == self._memory_file.tell():
            return
        if self._segment is None:
            # We have our first non-zero byte position. This means the init has just
            # been written. Create a Segment and put it to the queue of each output.
            self._segment = Segment(
                sequence=self._sequence,
                stream_id=self._stream_id,
                init=self._memory_file.getvalue(),
            )
            self._memory_file_pos = self._memory_file.tell()
            self._part_start_dts = self._segment_start_dts
            # Fetch the latest StreamOutputs, which may have changed since the
            # worker started.
            for stream_output in self._outputs_callback().values():
                stream_output.put(self._segment)
        else:  # These are the ends of the part segments
            self.flush(packet, last_part=False)

    def flush(self, packet: av.Packet, last_part: bool) -> None:
        """Output a part from the most recent bytes in the memory_file.

        If last_part is True, also close the segment, give it a duration,
        and clean up the av_output and memory_file.
        """
        if last_part:
            # Closing the av_output will write the remaining buffered data to the
            # memory_file as a new moof/mdat.
            self._av_output.close()
        assert self._segment
        self._memory_file.seek(self._memory_file_pos)
        self._segment.parts.append(
            Part(
                duration=float((packet.dts - self._part_start_dts) * packet.time_base),
                has_keyframe=self._part_has_keyframe,
                data=self._memory_file.read(),
            )
        )
        if last_part:
            self._segment.duration = float(
                (packet.dts - self._segment_start_dts) * packet.time_base
            )
            self._memory_file.close()  # We don't need the BytesIO object anymore
        else:
            self._memory_file_pos = self._memory_file.tell()
            self._part_start_dts = packet.dts
        self._part_has_keyframe = False

    def discontinuity(self) -> None:
        """Mark the stream as having been restarted."""
        # Preserving sequence and stream_id here keep the HLS playlist logic
        # simple to check for discontinuity at output time, and to determine
        # the discontinuity sequence number.
        self._stream_id += 1

    def close(self) -> None:
        """Close stream buffer."""
        self._av_output.close()
        self._memory_file.close()


class TimestampValidator:
    """Validate ordering of timestamps for packets in a stream."""

    def __init__(self) -> None:
        """Initialize the TimestampValidator."""
        # Decompression timestamp of last packet in each stream
        self._last_dts: dict[av.stream.Stream, float] = {}
        # Number of consecutive missing decompression timestamps
        self._missing_dts = 0

    def is_valid(self, packet: av.Packet) -> float:
        """Validate the packet timestamp based on ordering within the stream."""
        # Discard packets missing DTS. Terminate if too many are missing.
        if packet.dts is None:
            if self._missing_dts >= MAX_MISSING_DTS:
                raise StopIteration(
                    f"No dts in {MAX_MISSING_DTS+1} consecutive packets"
                )
            self._missing_dts += 1
            return False
        self._missing_dts = 0
        # Discard when dts is not monotonic. Terminate if gap is too wide.
        prev_dts = self._last_dts.get(packet.stream, float("-inf"))
        if packet.dts <= prev_dts:
            gap = packet.time_base * (prev_dts - packet.dts)
            if gap > MAX_TIMESTAMP_GAP:
                raise StopIteration(
                    f"Timestamp overflow detected: last dts = {prev_dts}, dts = {packet.dts}"
                )
            return False
        self._last_dts[packet.stream] = packet.dts
        return True


def stream_worker(
    source: str,
    options: dict[str, str],
    segment_buffer: SegmentBuffer,
    quit_event: Event,
) -> None:
    """Handle consuming streams."""

    try:
        container = av.open(source, options=options, timeout=SOURCE_TIMEOUT)
    except av.AVError:
        _LOGGER.error("Error opening stream %s", redact_credentials(str(source)))
        return
    try:
        video_stream = container.streams.video[0]
    except (KeyError, IndexError):
        _LOGGER.error("Stream has no video")
        container.close()
        return
    try:
        audio_stream = container.streams.audio[0]
    except (KeyError, IndexError):
        audio_stream = None
    # These formats need aac_adtstoasc bitstream filter, but auto_bsf not
    # compatible with empty_moov and manual bitstream filters not in PyAV
    if container.format.name in {"hls", "mpegts"}:
        audio_stream = None
    # Some audio streams do not have a profile and throw errors when remuxing
    if audio_stream and audio_stream.profile is None:
        audio_stream = None

    # Iterator for demuxing
    container_packets: Iterator[av.Packet]
    # The video dts at the beginning of the segment
    segment_start_dts: int | None = None
    # Because of problems 1 and 2 below, we need to store the first few packets and replay them
    initial_packets: deque[av.Packet] = deque()

    # Have to work around two problems with RTSP feeds in ffmpeg
    # 1 - first frame has bad pts/dts https://trac.ffmpeg.org/ticket/5018
    # 2 - seeking can be problematic https://trac.ffmpeg.org/ticket/7815

    def peek_first_dts() -> bool:
        """Initialize by peeking into the first few packets of the stream.

        Deal with problem #1 above (bad first packet pts/dts) by recalculating using pts/dts from second packet.
        Also load the first video keyframe dts into segment_start_dts and check if the audio stream really exists.
        """
        nonlocal segment_start_dts, audio_stream, container_packets
        found_audio = False
        try:
            # Ensure packets are ordered correctly
            dts_validator = TimestampValidator()
            container_packets = filter(
                dts_validator.is_valid, container.demux((video_stream, audio_stream))
            )
            first_packet: av.Packet | None = None
            # Get to first video keyframe
            while first_packet is None:
                packet = next(container_packets)
                if packet.stream == audio_stream:
                    found_audio = True
                elif packet.is_keyframe:  # video_keyframe
                    first_packet = packet
                    initial_packets.append(packet)
            # Get first_dts from subsequent frame to first keyframe
            while segment_start_dts is None or (
                audio_stream
                and not found_audio
                and len(initial_packets) < PACKETS_TO_WAIT_FOR_AUDIO
            ):
                packet = next(container_packets)
                if packet.stream == audio_stream:
                    # detect ADTS AAC and disable audio
                    if audio_stream.codec.name == "aac" and packet.size > 2:
                        with memoryview(packet) as packet_view:
                            if packet_view[0] == 0xFF and packet_view[1] & 0xF0 == 0xF0:
                                _LOGGER.warning(
                                    "ADTS AAC detected - disabling audio stream"
                                )
                                container_packets = filter(
                                    dts_validator.is_valid,
                                    container.demux(video_stream),
                                )
                                audio_stream = None
                                continue
                    found_audio = True
                elif (
                    segment_start_dts is None
                ):  # This is the second video frame to calculate first_dts from
                    segment_start_dts = packet.dts - packet.duration
                    first_packet.pts = first_packet.dts = segment_start_dts
                initial_packets.append(packet)
            if audio_stream and not found_audio:
                _LOGGER.warning(
                    "Audio stream not found"
                )  # Some streams declare an audio stream and never send any packets

        except (av.AVError, StopIteration) as ex:
            _LOGGER.error(
                "Error demuxing stream while finding first packet: %s", str(ex)
            )
            return False
        return True

    if not peek_first_dts():
        container.close()
        return

    segment_buffer.set_streams(video_stream, audio_stream)
    assert isinstance(segment_start_dts, int)
    segment_buffer.reset(segment_start_dts)

    # Rewind the stream and iterate over the initial set of packets again
    # filtering out any packets with timestamp ordering issues.
    packets = itertools.chain(initial_packets, container_packets)
    while not quit_event.is_set():
        try:
            packet = next(packets)
        except (av.AVError, StopIteration) as ex:
            _LOGGER.error("Error demuxing stream: %s", str(ex))
            break

        # Mux packets, and possibly write a segment to the output stream.
        # This mutates packet timestamps and stream
        segment_buffer.mux_packet(packet)

    # Close stream
    segment_buffer.close()
    container.close()