@type alignment() :: :au | :nalu

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

:nalu 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

@type framerate() :: {frames :: pos_integer(), seconds :: pos_integer()} | nil

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} If the information about the framerate is not present in the stream, nil value should be used.

@type height() :: 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. If the information about the height is not present in the stream, nil value should be used.

@type nalu_in_metadata() :: 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 or AVC prefix
• metadata: metadata - metadata that would be merged into the buffer metadata if alignment was :nalu.

@type profile() ::
  :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

@type stream_structure() :: :annexb | {:avc1 | :avc3, dcr :: binary()}

Describes H264 stream structure.

Annex B (ITU-T H.264 Recommendation) is suitable for writing to file or streaming with MPEG-TS. In this format each NAL unit is prefixed by three or four-byte start code (0x(00)000001) that allows to identify boundaries between them.

avc1 and avc3 are described by ISO/IEC 14496-15. In such stream a DCR (Decoder Configuration Record) is included out-of-band and NALUs lack the start codes, but are prefixed with their length. The length of these prefixes is contained in the stream's DCR. AVC streams are more suitable for placing in containers (e.g. they are used by QuickTime (.mov), MP4, Matroska and FLV). In avc1 streams PPSs and SPSs (Picture Parameter Sets and Sequence Parameter Sets) are transported in the DCR, when in avc3 they may be also present in the stream (in-band).

@type t() :: %Membrane.H264{
  alignment: alignment(),
  framerate: framerate(),
  height: height(),
  nalu_in_metadata?: nalu_in_metadata(),
  profile: profile(),
  stream_structure: stream_structure(),
  width: width()
}

Format definition for H264 video stream.

@type width() :: 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. If the information about the width is not present in the stream, nil value should be used.