View Source Membrane.H265.Parser (Membrane H.264 and H.265 plugin v0.10.0)

Membrane element providing parser for H265 encoded video stream.

The parser:

  • prepares and sends the appropriate stream format, based on information provided in the stream and via the element's options
  • splits the incoming stream into H265 access units - each buffer being output is a Membrane.Buffer struct with a binary payload of a single access unit
  • enriches the output buffers with the metadata describing the way the access unit is split into NAL units, type of each NAL unit making up the access unit and the information if the access unit hold a keyframe.

The parser works in one of three possible modes, depending on the structure of the input buffers:

  • :bytestream - each input buffer contains some part of H265 stream's payload, but not necessary a logical H265 unit (like NAL unit or an access unit). Can be used for i.e. for parsing the stream read from the file.
  • :nalu_aligned - each input buffer contains a single NAL unit's payload
  • :au_aligned - each input buffer contains a single access unit's payload

The parser's mode is set automatically, based on the input stream format received by that element:

  • Receiving %Membrane.RemoteStream{type: :bytestream} results in the parser mode being set to :bytestream
  • Receiving %Membrane.H265{alignment: :nalu} results in the parser mode being set to :nalu_aligned.
  • Receiving %Membrane.H265{alignment: :au} results in the parser mode being set to :au_aligned.

The parser also allows for conversion between stream structures. The available structures are:

  • Annex B, :annexb - In a stream with this structure each NAL unit is prefixed by three or four-byte start code (0x(00)000001) that allows to identify boundaries between them.
  • hvc1, :hvc1 - In such stream a DCR (Decoder Configuration Record) is included in stream_format and NALUs lack the start codes, but are prefixed with their length. The length of these prefixes is contained in the stream's DCR. PPSs, SPSs and VPSs (Picture Parameter Sets, Sequence Parameter Sets and Video Parameter Sets) are transported in the DCR.
  • hev1, :hev1 - The same as hvc1, only that parameter sets may be also present in the stream (in-band).

Element options

Passed via struct Membrane.H265.Parser.t/0

  • vpss

    [binary()]

    Default value: []
    Video Parameter Set NAL unit binary payloads - if absent in the stream, may be provided via this option (only available for :annexb output stream format)

    Any decoder conforming to the profiles specified in "Annex A" of ITU/IEC H265 (08/21), but does not support INBLD may discard all VPS NAL units.

  • spss

    [binary()]

    Default value: []
    Sequence Parameter Set NAL unit binary payloads - if absent in the stream, should be provided via this option (only available for :annexb output stream format).

  • ppss

    [binary()]

    Default value: []
    Picture Parameter Set NAL unit binary payloads - if absent in the stream, should be provided via this option (only available for :annexb output stream format).

  • skip_until_keyframe

    boolean()

    Default value: true
    Determines whether to drop the stream until the first key frame is received.

    Defaults to true.

  • repeat_parameter_sets

    boolean()

    Default value: false
    Repeat all parameter sets (vps, sps and pps) on each IRAP picture.

    Parameter sets may be retrieved from:

    • The stream
    • Parser options.
    • Decoder Configuration Record, sent in :hcv1 and :hev1 stream types
  • output_alignment

    :au | :nalu

    Default value: :au
    Alignment of the buffers produced as an output of the parser. If set to :au, each output buffer will be a single access unit. Otherwise, if set to :nalu, each output buffer will be a single NAL unit.

  • output_stream_structure

    nil | stream_structure() | :hvc1 | :hev1

    Default value: nil
    format of the outgoing H265 stream, if set to :annexb NALUs will be separated by a start code (0x(00)000001) or if set to :hvc1 or :hev1 they will be prefixed by their size. Additionally for :hvc1 and :hev1 a tuple can be passed containing the atom and nalu_length_size that determines the size in bytes of each NALU's field describing their length (by default 4). In hvc1 output streams the PPSs, SPSs and VPSs will be transported in the DCR, when in hev1 they will be present only in the stream (in-band). If not provided or set to nil the stream's structure will remain unchanged.

  • generate_best_effort_timestamps

    false | %{:framerate => {pos_integer(), pos_integer()}, optional(:add_dts_offset) => boolean()}

    Default value: false
    Generates timestamps based on given framerate.

    This option works only when Membrane.RemoteStream format arrives.

    Keep in mind that the generated timestamps may be inaccurate and lead to video getting out of sync with other media, therefore H265 stream should be kept in a container that stores the timestamps alongside.

    By default, the parser adds negative DTS offset to the timestamps, so that in case of frame reorder (which always happens when B frames are present) the DTS is always bigger than PTS. If that is not desired, you can set add_dts_offset: false.

    The calculated DTS/PTS may be wrong since we base it on access units' POC (Picture Order Count). We assume here that the POC is continuous on a CVS (Coded Video Sequence) which is not guaranteed by the H265 specification. An example where POC values may not be continuous is when generating sub-bitstream from the main stream by deleting access units belonging to a higher temporal sub-layer.

Pads

:input

Accepted formats:

%RemoteStream{type: :bytestream}
H265
Direction::input
Availability::always
Flow control::auto

:output

Accepted formats:

%H265{alignment: alignment, nalu_in_metadata?: true} when alignment in [:nalu, :au]
Direction::output
Availability::always
Flow control::auto

Summary

Types

Format of the H265 stream, if set to :annexb NALUs will be separated by a start code (0x(00)000001) or if set to :hvc1 or :hev1 they will be prefixed by their size.

t()

Struct containing options for Membrane.H265.Parser

Functions

Returns description of options available for this module

Types

@type stream_structure() ::
  :annexb | {codec_tag :: :hvc1 | :hev1, nalu_length_size :: pos_integer()}

Format of the H265 stream, if set to :annexb NALUs will be separated by a start code (0x(00)000001) or if set to :hvc1 or :hev1 they will be prefixed by their size.

@type t() :: %Membrane.H265.Parser{
  generate_best_effort_timestamps:
    false
    | %{
        :framerate => {pos_integer(), pos_integer()},
        optional(:add_dts_offset) => boolean()
      },
  output_alignment: :au | :nalu,
  output_stream_structure: nil | stream_structure() | :hvc1 | :hev1,
  ppss: [binary()],
  repeat_parameter_sets: boolean(),
  skip_until_keyframe: boolean(),
  spss: [binary()],
  vpss: [binary()]
}

Struct containing options for Membrane.H265.Parser

Functions

@spec options() :: keyword()

Returns description of options available for this module