Specs

alignment_t() :: :au | :nal | :none

Describes whether and how buffers are aligned.

:au means each buffer contains one Access Unit - all the NAL units required to decode a single frame of video

:nal aligned stream ensures that no NAL unit is split between buffers, but it is possible that NALUs required for one frame are in different buffers

:none means the stream hasn't been parsed and is not aligned.

Specs

framerate_t() :: {frames :: pos_integer(), seconds :: pos_integer()}

Number of frames per second. To avoid using floating point numbers, it is described by 2 integers number of frames per timeframe in seconds.

For example, NTSC's framerate of ~29.97 fps is represented by {30_000, 1001}

Specs

height_t() :: pos_integer()

Height of single frame in pixels.

Allowed values may be restricted by used encoding parameters, for example, when using 4:2:0 chroma subsampling dimensions must be divisible by 2.

Specs

nalu_in_metadata_t() :: boolean()

When alignment is set to :au, determines whether buffers have NALu info attached in metadata.

If true, each buffer contains the NAL units list under metadata.h264.nalus. The list consists of maps with the following entries:

• prefixed_poslen: {pos, len} - position and length of the NALu within the payload
• unprefixed_poslen: {pos, len} - as above, but omits Annex B prefix
• metadata: metadata - metadata that would be merged into the buffer metadata if alignment was :nal.

Specs

profile_t() ::
  :constrained_baseline
  | :baseline
  | :main
  | :high
  | :high_10
  | :high_422
  | :high_444
  | :high_10_intra
  | :high_422_intra
  | :high_444_intra

Profiles defining constraints for encoders and requirements from decoders decoding such stream

Specs

stream_format_t() :: :avc1 | :avc3 | :byte_stream

Describes h264 stream format.

Byte-stream format (often reffered to as 'Annex B' because it is defined in Annex B of ITU-T H.264 Recommendation) is suitable for writing to file or streaming with MPEG-TS. In this format each NAL unit is preceded by three or four-byte start code (0x(00)000001) that helps to identify boundaries.

avc1 and avc3 are described by ISO/IEC 14496-15. In such stream NALUs lack the start codes, but are preceded with their length. Avc streams are more suitable for placing in containers (e.g. they are used by QuickTime (.mov), MP4, Matroska and FLV). Avc1 and avc3 differ in how PPS and SPS (Picture Parameter Set and Sequence Parameter Set) are transported.

Specs

t() :: %Membrane.H264{
  alignment: alignment_t(),
  framerate: framerate_t(),
  height: height_t(),
  nalu_in_metadata?: nalu_in_metadata_t(),
  profile: profile_t(),
  stream_format: stream_format_t(),
  width: width_t()
}

Specs

width_t() :: pos_integer()

Width of single frame in pixels.

Allowed values may be restricted by used encoding parameters, for example, when using 4:2:0 chroma subsampling dimensions must be divisible by 2.