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SCTE-35, id3 markers, dynamic metadata

Overview

We discuss here about the ability to deal with dynamic metadata such as SCTE-35 in GPAC Filters. The information is this page applies to other metadata such as ID3 markers (e.g. Nielsen), timecodes (TEMI, QT), or virtually any type of dynamic metadata.

A special dec_scte35 filter allows to segment SCTE-35 content for 23001-18 CMAF Event Track creation.

GPAC is able to: - inspect, - remux or transmux, - segment for DASH, - create 23001-18 ISOBMFF Event Track (with emib and emeb boxes), - edit these data to some extend.

Inspection

The content can be inspect like any other content in GPAC. Packet-based inspection may allow to dump useful information for analysis and reprocessing.

GPAC inspect

gpac -i input inspect:analyze=full:deep:props

would output:

[...]
<Packet number="970" PID="1" framing="complete" dts="1636452" cts="1640956" dur="1502" sap="0" ilace="0" corr="0" seek="0" bo="N/A" roll="0" crypt="0" vers="0" size="6799" lp="0" depo="0" depf="0" red="0" CRC32="0x17CDFEAC">
 <SCTE35>
  <scte35:SpliceInfoSection xmlns:scte35="urn:scte:scte35:2013:bin" sap_type="3" protocol_version="0" encrypted_packet="0" pts_adjustment="183000" tier="4095">
   <scte35:SpliceInsert splice_event_id="4026531841" splice_event_cancel_indicator="False" out_of_network_indicator="True" program_splice_flag="True" duration_flag="False" splice_immediate_flag="False">
    <scte35:SpliceTime pts_time="1813812"/>
   </scte35:SpliceInsert>
  </scte35:SpliceInfoSection>
 </SCTE35>
</Packet>
[...]

MP4Box -dxml

MP4Box -dxml scte35.mp4

scte35_dump.xml would contain for instance such descriptions for a sample:

[...]
<NHNTSample number="94" DTS="41224943904144" dataLength="98" CTSOffset="0" isRAP="yes" mediaOffset="0" sourceByteOffset="13584" duration="48048" depends="24" >
<EventMessageInstanceBox Size="98" Type="emib" Version="0" Flags="0" Specification="EventMessageTrack" Container="file" presentation_time_delta="122121" event_duration="239239" event_id="1" scheme_id_uri="urn:scte:scte35:2013:bin" value="" message_data="0xFC302500000000697800FFF01405F00000027FEFFE1D0AC9C1FE000DB07B0001010100001231F90A" >
  <scte35:SpliceInfoSection xmlns:scte35="urn:scte:scte35:2013:bin" sap_type="3" protocol_version="0" encrypted_packet="0" pts_adjustment="27000" tier="4095">
   <scte35:SpliceInsert splice_event_id="4026531842" splice_event_cancel_indicator="False" out_of_network_indicator="True" program_splice_flag="True" duration_flag="True" splice_immediate_flag="False">
    <scte35:SpliceTime pts_time="487246273"/>
    <scte35:BreakDuration duration="897147"/>
   </scte35:SpliceInsert>
  </scte35:SpliceInfoSection>
</EventMessageInstanceBox>
</NHNTSample>
[...]

Remux and transmux

GPAC is able to remux any to any, including but not limited to: - TS to TS - MP4 (23001-18) to MP4 (23001-18) - TS to MP4 (23001-18)

See specific instructions in the next section when segmenting for OTT packaging (MPEG-DASH, HLS).

The command-line is trivial:

gpac -i input -o output

The format is selected automatically depending on the file extension (or can be forced with :ext=).

Segmentation and 23001-18 ISOBMFF Event Track

Adaptive streaming with DASH or HLS requires the content to be segmented. Simple segmentation (where content can be replicated over several segments without any change) works for all kind of streams.

For SCTE-35 streams the dec_scte35 filter must be explicitly loaded. Note that it can detect the segment duration from the dasher to create the right segmentation for you:

gpac -i input scte35dec -o output.mpd:segdur=2