core/homeassistant/components/stream/worker.py

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

from collections import deque
from collections.abc import Generator, Iterator, Mapping
from io import BytesIO
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 PeekIterator(Iterator):
    """An Iterator that may allow multiple passes.

    This may be consumed like a normal Iterator, however also supports a
    peek() method that buffers consumed items from the iterator.
    """

    def __init__(self, iterator: Iterator[av.Packet]) -> None:
        """Initialize PeekIterator."""
        self._iterator = iterator
        self._buffer: deque[av.Packet] = deque()
        # A pointer to either _iterator or _buffer
        self._next = self._iterator.__next__

    def __iter__(self) -> Iterator:
        """Return an iterator."""
        return self

    def __next__(self) -> av.Packet:
        """Return and consume the next item available."""
        return self._next()

    def _pop_buffer(self) -> av.Packet:
        """Consume items from the buffer until exhausted."""
        if self._buffer:
            return self._buffer.popleft()
        # The buffer is empty, so change to consume from the iterator
        self._next = self._iterator.__next__
        return self._next()

    def peek(self) -> Generator[av.Packet, None, None]:
        """Return items without consuming from the iterator."""
        # Items consumed are added to a buffer for future calls to __next__
        # or peek. First iterate over the buffer from previous calls to peek.
        self._next = self._pop_buffer
        for packet in self._buffer:
            yield packet
        for packet in self._iterator:
            self._buffer.append(packet)
            yield packet


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 is_keyframe(packet: av.Packet) -> Any:
    """Return true if the packet is a keyframe."""
    return packet.is_keyframe


def unsupported_audio(packets: Iterator[av.Packet], audio_stream: Any) -> bool:
    """Detect ADTS AAC, which is not supported by pyav."""
    if not audio_stream:
        return False
    for count, packet in enumerate(packets):
        if count >= PACKETS_TO_WAIT_FOR_AUDIO:
            # Some streams declare an audio stream and never send any packets
            _LOGGER.warning("Audio stream not found")
            break
        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")
                        return True
            break
    return False


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

    dts_validator = TimestampValidator()
    container_packets = PeekIterator(
        filter(dts_validator.is_valid, container.demux((video_stream, audio_stream)))
    )

    def is_video(packet: av.Packet) -> Any:
        """Return true if the packet is for the video stream."""
        return packet.stream == video_stream

    # 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
    #
    # Use a peeking iterator to peek into the start of the stream, ensuring
    # everything looks good, then go back to the start when muxing below.
    try:
        if audio_stream and unsupported_audio(container_packets.peek(), audio_stream):
            audio_stream = None
            container_packets = PeekIterator(
                filter(dts_validator.is_valid, container.demux(video_stream))
            )

        # Advance to the first keyframe for muxing, then rewind so the muxing
        # loop below can consume.
        first_keyframe = next(filter(is_keyframe, filter(is_video, container_packets)))
        # Deal with problem #1 above (bad first packet pts/dts) by recalculating
        # using pts/dts from second packet. Use the peek iterator to advance
        # without consuming from container_packets. Skip over the first keyframe
        # then use the duration from the second video packet to adjust dts.
        next_video_packet = next(filter(is_video, container_packets.peek()))
        start_dts = next_video_packet.dts - next_video_packet.duration
        first_keyframe.dts = first_keyframe.pts = start_dts
    except (av.AVError, StopIteration) as ex:
        _LOGGER.error("Error demuxing stream while finding first packet: %s", str(ex))
        container.close()
        return

    segment_buffer.set_streams(video_stream, audio_stream)
    segment_buffer.reset(start_dts)

    # Mux the first keyframe, then proceed through the rest of the packets
    segment_buffer.mux_packet(first_keyframe)

    while not quit_event.is_set():
        try:
            packet = next(container_packets)
        except (av.AVError, StopIteration) as ex:
            _LOGGER.error("Error demuxing stream: %s", str(ex))
            break
        segment_buffer.mux_packet(packet)

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