Stream descriptors

There can be multiple stream_descriptor with input from the same “file” or multiple different “files”.

Stream descriptor is of the form:

<field>=<value>[,<field>=<value>]...

These are the available fields:

input (in):

input/source media “file” path, which can be regular files, pipes, udp streams. See UDP file options on additional options for UDP files.

stream_selector (stream):

Required field with value ‘audio’, ‘video’, ‘text’ or stream number (zero based).

output (out):

Required output file path (single file).

init_segment:

initialization segment path (multiple file).

segment_template (segment):

Optional value which specifies the naming pattern for the segment files, and that the stream should be split into multiple files. Its presence should be consistent across streams. See Segment template formatting.

bandwidth (bw):

Optional value which contains a user-specified maximum bit rate for the stream, in bits/sec. If specified, this value is propagated to (HLS) EXT-X-STREAM-INF:BANDWIDTH or (DASH) Representation@bandwidth and the $Bandwidth$ template parameter for segment names. If not specified, the bandwidth value is estimated from content bitrate. Note that it only affects the generated manifests/playlists; it has no effect on the media content itself.

language (lang):

Optional value which contains a user-specified language tag. If specified, this value overrides any language metadata in the input stream.

output_format (format):

Optional value which specifies the format of the output files (MP4 or WebM). If not specified, it will be derived from the file extension of the output file.

For subtitles in MP4, you can specify ‘vtt+mp4’ or ‘ttml+mp4’ to control which text format is used.

input_format (format):

Optional value which specifies the format of the input files or streams. If not specified, it will be autodetected, which in some cases may fail.

For example, a live UDP WebVTT input stream may be up and streaming long before a shaka packager instance consumes it, and therefore shaka packager never gets the initial “WEBVTT” header string. In such a case, shaka packager can’t properly autodetect the stream format as WebVTT, and thus doesn’t process it. But stating ‘input_format=webvtt’ as selector parameter will tell shaka packager to omit autodetection and consider WebVTT format for that stream.

trick_play_factor (tpf):

Optional value which specifies the trick play, a.k.a. trick mode, stream sampling rate among key frames. If specified, the output is a trick play stream.

cc_index:

Optional value which specifies the index/ID of the subtitle stream to use for formats where multiple exist within the same stream. For example, CEA allows specifying up to 4 streams within a single video stream. If not specified, all subtitles will be merged together.

forced_subtitle:

Optional boolean value (0|1). If set to 1 indicates that this stream is a Forced Narrative subtitle that should be displayed when subtitles are otherwise off, for example used to caption short portions of the audio that might be in a foreign language. For DASH this will set role to forced_subtitle, for HLS it will set FORCED=YES and AUTOSELECT=YES. Only valid for subtitles.

DRM related Stream descriptor fields

skip_encryption=0|1:

Optional. Defaults to 0 if not specified. If it is set to 1, no encryption of the stream will be made.

drm_label:

Optional value for custom DRM label, which defines the encryption key applied to the stream. Typically values include AUDIO, SD, HD, UHD1, UHD2. For raw key, it should be a label defined in –keys. If not provided, the DRM label is derived from stream type (video, audio), resolutions, etc. Note that it is case sensitive.

DASH specific stream descriptor fields

dash_accessibilities (accessibilities):

Optional semicolon separated list of values for DASH Accessibility element. The value should be in the format: scheme_id_uri=value, which propagates to the Accessibility element in the result DASH manifest. See DASH (ISO/IEC 23009-1) specification for details.

dash_roles (roles):

optional semicolon separated list of values for DASH Role element. The value should be one of: caption, subtitle, main, alternate, supplementary, commentary, dub, description, sign, metadata, enhanced-audio- intelligibility, emergency, forced-subtitle, easyreader, and karaoke.

See DASH (ISO/IEC 23009-1) specification for details.

HLS specific stream descriptor fields

hls_name:

Used for HLS audio to set the NAME attribute for EXT-X-MEDIA. Defaults to the base of the playlist name.

hls_group_id:

Used for HLS audio to set the GROUP-ID attribute for EXT-X-MEDIA. Defaults to ‘audio’ if not specified.

playlist_name:

The HLS playlist file to create. Usually ends with ‘.m3u8’, and is relative to hls_master_playlist_output (see below). If unspecified, defaults to something of the form ‘stream_0.m3u8’, ‘stream_1.m3u8’, ‘stream_2.m3u8’, etc.

iframe_playlist_name:

The optional HLS I-Frames only playlist file to create. Usually ends with ‘.m3u8’, and is relative to hls_master_playlist_output (see below). Should only be set for video streams. If unspecified, no I-Frames only playlist is created.

hls_characteristics (charcs):

Optional colon or semi-colon separated list of values for the CHARACTERISTICS attribute for EXT-X-MEDIA. See CHARACTERISTICS attribute in http://bit.ly/2OOUkdB for details.