Standards: Part 9 - Standards For On-air Broadcasting & Streaming Services
Traditional on-air broadcasters and streaming service providers use many of the same standards to define how content is received from external providers and how it is subsequently delivered to the consumer. They may apply those standards in slightly different ways.
This article is part of our growing series on Standards.
There is an overview of all 26 articles in Part 1 - An Introduction To Standards.
Streamed Vs. Linear Broadcast Architectures
One of the important differences is the way colorimetry is specified. The range of colors is constrained in traditional broadcasting because illegal colors cannot be reliably transported through the systems. This is due to legacy limitations existing long after analog video has been deprecated. Streaming services are not limited because they never used analog video.
Streaming services are wholly file-based. Instead, a streaming server can deliver the contents of a file made by the production workflow. This file would have already been prepared for streaming and no further compression is needed. Live feeds are presented as virtual files.
On-air head-end systems multiplex several channels of uncompressed material into a transport stream. Live material is piped direct from the studio gallery and files are injected as if they were live feeds.
Where The Standards Apply
Here is a typical broadcast system transmitting linear content. This might originate from an external source or as pre-recorded programmes played out to the transmission system.
The architecture is quite different for a streaming Video-On-Demand (VOD) service. The playout and transmission are replaced by a request driven Content Delivery Network (CDN).
The applicable ingest standards are described in delivery specifications based on the individual broadcaster's needs.
Delivery Specifications
The delivery specifications define file formats, metadata and supporting media for external production companies when they supply content.
Netflix has a delivery specification geared towards streaming services. Other streaming services will likewise have their own specifications. This is necessary when content is arriving from many diverse sources and facilitates the ingest by automated systems.
Public service on-air broadcasters in the UK have formed the Digital Production Partnership (DPP) to pool their expertise. They are:
- BBC
- BT Sport
- Channel 4
- Channel 5
- ITV
- Sky
- STV
- TG4
The DPP has a liaison with the North American Broadcast Association (NABA). The DPP also works closely with other standards bodies and has a membership of over 500 media, production and broadcasting companies. You can also join as an individual.
The collaboration with NABA has yielded a common file format based on IMF for the exchange of program material. This is published by SMPTE as TSP 2121.
Netflix also specifies the IMF format but check carefully for important differences.
The public-service broadcasters are all regulated in the UK by Ofcom. Each country has its own Regulatory Authority. Streaming services are not currently regulated in the same way although this may change. The Ofcom broadcasting code is incorporated into the delivery specifications for DPP organizations and adds these requirements:
- Photosensitive Epilepsy guidelines.
- Younger viewers should be protected from seeing or hearing harmful content.
- Equality and discrimination must be taken into account to support disabled viewers.
- Strict taste and decency guidelines are enforced and verified by inspecting compliance recordings.
Delivery specifications also cover metadata and other ancillary items such as sub-title texts, supporting still photographs and poster artworks which are included in the manifest.
Netflix and DPP both indicate that Apple ProRes coded video in an iTunes compatible container is also acceptable.
SMPTE ST 2067 IMF Files
The Interoperable Master Format (IMF) is the foundation for a lot of other file formats which are described as 'IMF Applications' in ST 2067. Application 2 extended (part 21) is specified by Netflix and the DPP as a potential delivery format.
The ST 2067 standard has many parts, not all of which are applicable in every situation. The parts are grouped into categories according to what they describe:
Part range | Description |
---|---|
1 - 19 | Core specifications. |
20 - 29 | Application 2 Studio Profile, JPEG 2000 coding. |
30 - 39 | Application 3 - Studio Profile, MPEG-4 coding. |
40 - 49 | Application 4 - Cinema Mezzanine. |
50 - 59 | Application 5 - ACES image format coding. |
60 - 69 | Application 6 - UHDTV with AVC codecs. |
70 - 79 | Application 7- VC-3 or VC-6 codecs. |
100 - 119 | Output Profiles. |
200 - 219 | IMF Plugins for extended functionality. |
Here is a list of the currently released parts with their revision dates:
Standard | Version | Description |
---|---|---|
OV 2067-0 | 2021 | Overview and roadmap document. |
ST 2067-3 | 2020 | Composition Playlist. |
ST 2067-4 | In progress | Virtual Track Fingerprint. |
ST 2067-5 | 2020 | Essence Component. |
ST 2067-8 | 2013 | Common Audio Labels. |
ST 2067-21 | 2016 | Early version of Application 2 Extended file packaging with monophonic audio. |
ST 2067-21 | 2020 | Application 2 Extended file packaging which supports stereo audio. |
ST 2067-21 | 2022 | Latest version of the Application 2 Extended file packaging. Includes revisions to colorimetry not yet widely supported in delivery specifications. |
ST 2067-30 | 2013 | Application 3 file packaging. |
ST 2067-40 | 2020 | Application 4 file packaging for Cinema Mezzanine use. |
ST 2067-50 | 2018 | Application 5 file packaging using ST 2065-1 (ACES) image essence format. |
ST 2067-60 | 2022 | Application 6 file packing for UHDTV program workflow (AVC). |
ST 2067-70 | Draft | Application file packaging using 2019-1 (VC-3) video essence format. |
ST 2067-71 | Draft | Mapping of VC-6 into IMF files. |
ST 2067-100 | 2014 | Output Profile List. |
ST 2067-101 | 2018 | Output Profile List – Common Image Definitions and Macros. |
ST 2067-102 | 2022 | Common Image Pixel Color Schemes. |
ST 2067-103 | 2020 | Output Profile List — Common Audio Definition and Macros. |
ST 2067-200 | 2018 | Dynamic Metadata for Color Volume Transform (DMCVT) Plug-in. |
ST 2067-201 | 2019 | Immersive Audio Bitstream Level-0 Plug-in. Specified by Netflix for surround-sound programs. |
ST 2067-201 | 2021 | Latest version of the Immersive Audio Bitstream Level-0 Plug-in. |
IMF Application DPP - TSP 2121
The SMPTE TSP 2121 standard is the basis of the DPP file format. This is an IMF Application and developed with NABA in the USA. Refer to other standards when necessary. ST 2067 will be useful as will the colorimetry specifications from the ITU.
Standard | Version | Description |
---|---|---|
TSP-2121 | 2018 | IMF application defined by DPP to support Apple ProRes, JPEG 2000 and H.264 coded video. |
TSP 2121-1 | 2018 | Technical specifications document. |
TSP 2121-1b | 2018 | RDD-6 Audio Metadata Schema. Description and Guide to the Use of the Dolby® E Audio Metadata Serial Bitstream. |
ER 2121-2 | 2019 | Business requirements document. |
ER 2121-3 | 2019 | Project log with collected comments and observations. |
TSP 2121-4 | 2019 | Technical specifications document. |
RDD 6 | 2018 | See TSP 2121-1b. |
RDD 59-1 | 2022 | Application DPP (ProRes). |
AS-11 DPP Schema | 2018 | The schema for AS-11 metadata to be associated with a composition. |
AG-08 | In progress | Licensing document. |
Colorimetry Specifications
This is a complex subject. Human visual perception naturally compensates for color shifts, different dynamic ranges and brightness levels.
The colorimetry standards describe transfer functions that map the input brightness levels to the output. When the output color gamut cannot include all the colors in the input, the transfer function ensures the image is perceived correctly under all viewing conditions.
Video color legalization in traditional broadcasting limits the dynamic range of pixel color values. Streaming services are not affected by this and can accommodate the full range of values.
Basic transfer functions are implemented with Gamma correction shown here with positive and negative values alongside the unmodified linear transform.
Dolby Laboratories developed a more sophisticated technique for displaying High Dynamic Range (HDR) content. This is called the Perceptual Quantizer (PQ). It greatly enhances the detail in the darker regions of the image. This is a simplified example with the positive Gamma curve to show the difference.
The BBC collaborated with NHK on an alternative approach called Hybrid Log-Gamma (HLG). This applies gamma correction to the lower range of values and logarithmic correction to the upper. It doesn't increase detail in the dark region as much as PQ. The mid-range values are increased more than the basic Gamma transform but less than PQ. The join between the two curves must be implemented carefully to avoid discontinuities that would introduce contouring (posterization) artefacts in the output images. The positive Gamma curve is included for comparison.
Here are some relevant colorimetry standards:
Standard | Version | Description |
---|---|---|
ST 2084 | 2014 | High Dynamic Range Electro-Optical Transfer Function of Mastering Reference Displays. The Perceptual Quantizer (PQ) is used as the Colorimetry specification for Dolby Vision™️ HDR content. |
ST-2086 | 2018 | Mastering Display Color Volume Metadata Supporting High Luminance and Wide-Color Gamut Images. |
ITU-R BT.709 | 2015 | Parameter values for the HDTV standards for production and international program exchange. |
ITU-R BT.1886 | 2011 | Reference electro-optical transfer function for flat panel displays used in HDTV studio production. |
ITU-R BT.2020 | 2015 | Parameter values for Ultra-High Definition television systems for production and international program exchange. |
ITU-R BT.2100 | 2018 | Image parameter values for High Dynamic Range television for use in production and international program exchange. Describes both the PQ and the Hybrid Log-Gamma transfer function. |
CIE D65 | 1967 | Specification of the white point for a color temperature of 6504 degrees Kelvin. Described in ITU-R BT 709 where the gamut is limited for use in TV systems. |
P3-D65 | 2015 | Wide-Color Gamut colorimetry specification for Dolby Vision™️ HDR content. Also limited by ITU-R BT 709. The P3 color space was originally developed by Apple Inc. |
Dolby Vision™️ CM 2.9 | 2018* | Dynamic Mastering Metadata for Color Volume Transformation. |
Dolby Vision™️ CM 4.0 | 2023* | Recommended and improved Dynamic Mastering Metadata for Color Volume Transformation with enhanced algorithms and a more complex tone-curve that supports additional post-processing options. This is a superset of the version 2.9 specification. |
* The version dates for the Dolby Vision metadata specs are approximate and based on available documentation.
DVB Standards For On-air Broadcasting
The Digital Video Broadcasting organization (DVB) manages a collection of international open-standards that describe how to transmit digital TV services on-air. DVB is a not-for-profit consortium sponsored by the broadcasters. Their standards are grouped into these categories:
Category | Description |
---|---|
Broadband delivery | For integration with IP delivered content. |
Interactivity | Interactive TV app and service design. |
Interfacing | Integration with broadcast infrastructure. |
Measurement | Service delivery monitoring and measurement. |
Metadata | Program guides, content and service discovery. |
Middleware | Integration with client platform hardware. |
Research | Investigative work. |
Security | Access control to paid content. |
Source coding & multiplexing | Coding of video and audio into transport streams for delivery. |
Subtitling | Ancillary services to support accessibility. |
Transmission | Delivery of content and services. |
The DVB standards have been the foundation for digital TV deployments worldwide and describe how TV signals can be transmitted in different ways:
Medium | Abbr | Description |
---|---|---|
Terrestrial | DTT | Regional broadcasts from a mast mounted antenna. Supplementary channels linked from the EPG are delivered by broadband. |
Satellite | DSat | National coverage from a satellite transponder, received via a dish. Supplementary channels delivered by broadband can also allow feedback and interaction from the viewer. |
Cable | DCable | Cable services are evolving towards broadband IPTV technologies which supports video on demand (VOD) content. |
The most familiar DVB standards describe how digital TV services are structured for transmission. The second-generation variants add high definition support:
Standard | Description |
---|---|
DVB-T | Terrestrial broadcasting. |
DVB-T2 | Second generation terrestrial (Hi-Def). |
DVB-H | Terrestrial broadcasts for reception on handheld devices. |
DVB-S | Satellite broadcasting. |
DVB-S2 | Second generation satellite (Hi-Def). |
DVB-C | Cable broadcasting (Tethered). |
DVB-C2 | Second generation cable (Hi-Def). |
DVB-CI | Common Interface for access control. |
Multiple program streams are packaged into a bundle. On DTT services, these are called Multiplexes and on DSat they are described as Transponders. The bundle also includes metadata for Service Information (SI) to populate Electronic Program Guides (EPG).
Conclusion
The SMPTE IMF file format is an industry standard preferred by many organizations that need to share content. Whilst there are alternatives that may be technically superior, some of them are proprietary.
The Dolby Vision™️ work on colorimetry has facilitated the wide adoption of High Dynamic Range (HDR) content which enhances the Ultra High Definition (UHD) viewing experience to a very high standard. There are open and non-proprietary alternatives if you need them.
The creation of world-wide standards such as TSP 2121 move us closer to content that can be deployed in many countries with little or no post-processing required.
If this level of collaboration continues, the future does look very encouraging but it will depend on agreed standards to make it all work.
These Appendix articles contain additional information you may find useful:
Part of a series supported by
You might also like...
Brazil Adopts ATSC 3.0 For NextGen TV Physical Layer
The decision by Brazil’s SBTVD Forum to recommend ATSC 3.0 as the physical layer of its TV 3.0 standard after field testing is a particular blow to Japan’s ISDB-T, because that was the incumbent digital terrestrial platform in the country. C…
Designing IP Broadcast Systems: System Monitoring
Monitoring is at the core of any broadcast facility, but as IP continues to play a more important role, the need to progress beyond video and audio signal monitoring is becoming increasingly important.
Broadcasting Innovations At Paris 2024 Olympic Games
France Télévisions was the standout video service performer at the 2024 Paris Summer Olympics, with a collection of technical deployments that secured the EBU’s Excellence in Media Award for innovations enabled by application of cloud-based IP production.
Standards: Part 18 - High Efficiency And Other Advanced Audio Codecs
Our series on Standards moves on to discussion of advancements in AAC coding, alternative coders for special case scenarios, and their management within a consistent framework.
HDR & WCG For Broadcast - Expanding Acquisition Capabilities With HDR & WCG
HDR & WCG do present new requirements for vision engineers, but the fundamental principles described here remain familiar and easily manageable.