H.264 hardware transcoder using Vulkan Video extensions.

Accepts a single H.264 input stream and produces multiple independently configured H.264 output streams. Each output pad is configured via pad options passed through via_out/2.

Example

spec = [
  child(:source, source)
  |> child(:parser, %Membrane.H264.Parser{...})
  |> child(:transcoder, Membrane.VKVideo.Transcoder),
  get_child(:transcoder)
  |> via_out(Pad.ref(:output, 0), options: [width: 1280, height: 720])
  |> child(:sink_hd, sink_hd),
  get_child(:transcoder)
  |> via_out(Pad.ref(:output, 1), options: [width: 640, height: 360])
  |> child(:sink_sd, sink_sd)
]

Element options

Passed via struct Membrane.VKVideo.Transcoder.t/0

• approx_framerate

  {non_neg_integer(), pos_integer()} | nil

  Default value: nil
  Framerate of the input stream expressed as {numerator, denominator}. It's only used by the rate control mechanism and therefore does not need to be an exact value. If nil, the framerate will be read from the stream format's structure or set to a fixed value of 30 frames per second if framerate is not provided by the stream format.

Pads

:input

Accepted formats:

%Membrane.H264{stream_structure: :annexb, alignment: :au}

:output

Accepted formats:

%Membrane.H264{stream_structure: :annexb, alignment: :au}

Pad options:

• width

  non_neg_integer()

  Required
  Output frame width in pixels.

• height

  non_neg_integer()

  Required
  Output frame height in pixels.

• tune

  :low_latency | :high_quality

  Default value: :low_latency
  Specifies whether the encoder should be optimized for minimal latency (which is important in case of livestreams) or for higher quality (applicable to offline encoding).

• rate_control

  :encoder_default
  | :disabled
  | {:variable_bitrate, Membrane.VKVideo.Encoder.VariableBitrate.t()}
  | {:constant_bitrate, Membrane.VKVideo.Encoder.ConstantBitrate.t()}

  Default value: :encoder_default
  Rate control mode for the output stream. See Membrane.VKVideo.Encoder for available options.

• scaling_algorithm

  :nearest_neighbor | :lanczos3 | :bilinear

  Default value: :bilinear
  Algorithm used when scaling the input to the output resolution.