View Source Membrane.H264.Parser (Membrane H264 plugin v0.5.1)
Membrane element providing parser for H264 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 h264 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 h264 stream's payload, but not necessary a logical h264 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.H264.RemoteStream{alignment: :nalu}
results in the parser mode being set to:nalu_aligned
- Receiving
%Membrane.H264.RemoteStream{alignment: :au}
results in the parser mode being set to:au_aligned
The distinguishment between parser modes was introduced to eliminate the redundant operations and to provide a reliable way for rewriting of timestamps:
- in the
:bytestream
mode:- if option
:framerate
is set to nil, the output buffers have their:pts
and:dts
set to nil - if framerate is specified,
:pts
and:dts
will be generated automatically, based on that framerate, starting from 0 This may only be used with h264 profiles:baseline
and:constrained_baseline
, wherePTS==DTS
.
- if option
- in the
:nalu_aligned
mode, the output buffers have their:pts
and:dts
set to:pts
and:dts
of the input buffer that was holding the first NAL unit making up given access unit (that is being sent inside that output buffer). - in the
:au_aligned
mode, the output buffers have their:pts
and:dts
set to:pts
and:dts
of the input buffer (holding the whole access unit being output)
element-options
Element options
Passed via struct Membrane.H264.Parser.t/0
sps
binary()
Default value:
""
Sequence Parameter Set NAL unit binary payload - if absent in the stream, should be provided via this option.pps
binary()
Default value:
""
Picture Parameter Set NAL unit binary payload - if absent in the stream, should be provided via this option.framerate
{pos_integer(), pos_integer()} | nil
Default value:
nil
Framerate of the video, represented as a tuple consisting of a numerator and the denominator. Its value will be sent inside the output Membrane.H264 stream format.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. Defaults to:au
.skip_until_keyframe?
boolean()
Default value:
false
Determines whether to drop the stream until the first key frame is received.Defaults to false.
repeat_parameter_sets
boolean()
Default value:
false
Repeat all parameter sets (sps
andpps
) on each IDR picture.Parameter sets may be retrieved from:
- The bytestream
Parser
options.- Decoder Configuration Record, sent as decoder_configuration_record
in
Membrane.H264.RemoteStream
stream format
pads
Pads
input
:input
Accepted formats:
%RemoteStream{type: :bytestream}
%H264{alignment: alignment} when alignment in [:nalu, :au]
%H264.RemoteStream{alignment: alignment} when alignment in [:nalu, :au]
Direction: | :input |
Availability: | :always |
Flow control: | :auto |
Demand unit: | :buffers |
output
:output
Accepted formats:
%H264{alignment: alignment, nalu_in_metadata?: true} when alignment in [:nalu, :au]
Direction: | :output |
Availability: | :always |
Flow control: | :auto |
Demand unit: | nil |
Link to this section Summary
Types
Struct containing options for Membrane.H264.Parser
Link to this section Types
@type t() :: %Membrane.H264.Parser{ framerate: {pos_integer(), pos_integer()} | nil, output_alignment: :au | :nalu, pps: binary(), repeat_parameter_sets: boolean(), skip_until_keyframe?: boolean(), sps: binary() }
Struct containing options for Membrane.H264.Parser
Link to this section Functions
@spec options() :: keyword()
Returns description of options available for this module