Technical Specifications for High Definition (HD) TV Interconnection to BDUs and Down-conversion to Standard Definition (SD)

Technical Specifications for High Definition (HD) TV Interconnection to BDUs and Down-conversion to Standard Definition (SD) Document Version 1.4 – A...
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Technical Specifications for High Definition (HD) TV Interconnection to BDUs and Down-conversion to Standard Definition (SD)

Document Version 1.4 – Aug. 15, 2011

Technical Specifications for High Definition (HD) TV Interconnection to BDUs and Down-conversion to Standard Definition (SD)

1.

SCOPE OF THIS DOCUMENT Section 4 – “HD Signal Interconnection between CBC/Radio-Canada and BDUs” of this document defines several types of interconnections between CBC/RadioCanada’s premises and the Broadcasting Distribution Undertaking (BDU) for the distribution of High Definition (HD) television programs. Section 5 – “HD to SD Signal Conversion Performed by the BDU” of this document defines specifications applying to all converters used in CBC/RadioCanada’s English and French networks’ TV programs. These programs are provided to BDUs in High Definition (HD) and need to be converted to Standard Definition (SD) for broadcast on conventional TV distribution platforms (analog NTSC and digital SD).

2.

INTRODUCTION In the near future, CBC/Radio-Canada will be migrating its satellite distribution platform from SD to HD. Once the migration is completed, programming in SD will no longer be available. Where required, BDUs will have to convert these HD signals into SD before distribution. HD-SDI is the recommended interconnection. There are, however, several other possible interconnections, such as ASI links, over-the-air or satellite links. CBC/Radio-Canada will retain the right to approve the interconnection format that will be used by each BDU. It will be up to the BDU to acquire (and transport, where applicable) the TV signal at the BDU’s expense. CBC/Radio-Canada’s policy further states that audio and video signals broadcast by owned stations or distributed to BDUs must meet Industry Canada’s technical specifications and recommendations. CBC/Radio-Canada’s goal is to adopt and promote the best possible practices in production and broadcasting, so as to deliver television programming of optimum quality to its audience. This technical specifications document is intended for all BDUs distributing SD channels generated from HD content supplied by CBC/Radio-Canada’s English and French networks. This document should permit the selection of HD to SD converters having sufficient performance to adjust their parameters toward the generation of SD content that meets CBC/Radio-Canada’s requirements. This document includes references to standards used in the broadcast industry. All specifications contained in these standards must be met. Note:

BDUs can contact CBC/Radio-Canada for further information concerning HD-SD converter products that meet the required specifications described in this document.

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3.

TERMINOLOGY

BDU

Broadcasting Distribution Undertaking: This term refers to a CRTClicensed undertaking that distributes broadcasting services to subscribers predominantly over a closed transmission system.

HD

High Definition: This term is used to describe native high definition productions, live or on tape, carrying High Definition signals. It is also used to designate broadcasting on CBC/Radio-Canada’s digital TV network in high definition mode.

SD

Standard Definition: This term is used to describe native standard definition productions, live or on tape, carrying standard definition signals. It encompasses analog and digital signals and formats. It is also used to designate broadcasting on CBC/Radio-Canada’s conventional television (SDTV) network.

AFD

Active Format Description: This term describes a video picture in terms of the aspect ratio and other characteristics of the active image within a coded frame. For example, an active image excludes bars in letterbox and pillarbox modes.

Postage Stamp

A display wherein the image is boxed in a border obtained by cascading several different aspect ratio conversions.

Dialnorm

The dialogue normalization (dialnorm) value indicates how far the average dialogue level of the encoded audio program is below digital 100% full scale (0 dBFS). CBC/Radio-Canada’s standard for the dialnorm value is –24 dBFS.

Described Video (DV)

The described video channel is a mono mix derived from the main program to which descriptive commentary is added.

Lo/Ro

(Left Only / Right Only) Conventional stereo signal.

Lt/Rt

(Left Total / Right Total) Matrix-encoded stereo signal in either Dolby® Surround or Dolby® Pro Logic II™.

Dolby® Surround, Pro Logic™

Dolby technology that combines four audio channels into a matrixencoded two-channel Lt/Rt signal, allowing multi-channel audio to be delivered to homes through any stereo-only transmission. Any consumer system equipped with Dolby Pro Logic decoders can provide the four playback channels. At any time, the Lt/Rt signal can be listened to as a conventional stereo signal.

Dolby®, Pro Logic II™

Dolby technology that combines five audio channels into a matrixencoded two-channel Lt/Rt signal.

Dolby Digital™ (AC3)

Dolby coding technology that can deliver 1- to 5.1-channel audio programs in a variety of configurations, intended for distribution to the consumer through SD/HD digital television broadcast.

TS

Transport Stream. The MPEG transport stream (TS) is a standard format for transmission and storage of audio, video and data. It is

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specified in standard MPEG-2 Part 1, Systems.

4.

HD SIGNAL INTERCONNECTION BETWEEN CBC/RADIOCANADA AND BDU'S The following describes possible interconnections between CBC/Radio-Canada and BDUs. Each type of interconnection will require CBC/Radio-Canada’s approval.

4.1.

HD-SDI Interconnection (Recommended): HD-SDI is the recommended interconnection to BDUs. It is only available at CBC/Radio-Canada’s Toronto and Montreal production centres. CBC/RadioCanada provides 720p HD video and AC-3 audio signals that are multiplexed into an HD-SDI interfacing signal, as defined in the SMPTE 292M and SMPTE 299M standards. Upon reception of the HD-SDI signal, the BDU will demultiplex these signals. CBC/Radio-Canada will provide limited rack space for BDU encoding, multiplexing and transport equipment in Toronto or Montreal.

4.2.

ASI Interconnection: This type of interconnection is available at regional production centres where CBC/Radio-Canada own and operate over the air digital transmitters for the local station only. In this type of interconnection, compressed 720p HD video and AC3 audio signals are inserted into MPEG-2 TS packets that are carried by the ASI signal, as defined in the ETSI EN-50083-9 standard (DVB Blue book A010) and the ETSI TR 101 891 Guideline document. Upon reception of the ASI signal by the BDU, MPEG-2 TS packets are extracted and decoded to generate the uncompressed HD video signal.

4.3.

Over-the-Air Reception: MPEG-2 TS packets are extracted from the received signal and decoded to generate the uncompressed HD video signal.

4.4.

Satellite Link Interconnection: MPEG-2 TS packets are extracted from the received signal. A transcoder (MPEG4 to MPEG-2) will be required should the BDU decide to distribute compressed HD signals in MPEG-2 format. MPEG-2 TS packets are then decoded to generate the uncompressed HD video signal.

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Note:

Table 1 below shows the PID CBC/Radio-Canada programs.

assignment

standard

for

Table 1- PID Assignment Standard for CBC/Radio-Canada Programs

Format: Syntax: Number of Services: Encryption: First Service Number: PCR: PID Assignment: Program Number PAT PMT Video Main Audio Secondary Audio PCR

MPEG-2 TS DVB (Basic MPEG PIDs only) Variable None of the required services are encrypted 3 Embedded in the video PID (All values are hexadecimal) 3 0 30 31 34 35 31

4 0 40 41 44 45 41

5 0 50 51 54 55 51

6 0 60 61 64 65 61

7 0 70 71 74 75 71

8 0 80 81 84 85 81

9 0 90 91 94 95 91

A 0 A0 A1 A4 A5 A1

B 0 B0 B1 B4 B5 B1

C 0 C0 C1 C4 C5 C1

D 0 D0 D1 D4 D5 D1

E 0 E0 E1 E4 E5 E1

5.

HD TO SD SIGNAL CONVERSION PERFORMED BY BDU’S

5.1.

Video Signal Available at the Converter Input

5.1.1.

Interfacing Signal: HD-SDI at 1.485 /1.001 Gbps as per the SMPTE 292M standard.

5.1.2.

Video Format:

720p59.94 as per the SMPTE 296M standard

Video signals provided by CBC/Radio-Canada include the Active Format Description (AFD) information that specifies the active area of the image to be displayed.

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F 0 F0 F1 F4 F5 F1

Technical Specifications for High Definition (HD) TV Interconnection to BDUs and Down-conversion to Standard Definition (SD)

5.2.

Video Signal Processing

5.2.1.

The converter must convert HD images (1280 pixels x 720 lines in the format 720p59.94) into an SD format (720 pixels x 480 lines). The first active line of the converted image in SD is line 23.

5.2.2.

The HD to SD converter must do a color space conversion from the ITU-R BT.709 standard to the ITU-R BT.601 standard.

5.2.3.

Considering that an HD image has an aspect ratio of 16:9 and an SD image at the output has an aspect ratio of 4:3, an image aspect ratio conversion by means of a center cut (see Figure 1) or a letterbox (see Figure 2) must be made when the HD source is a full screen image. Currently, for CBC/Radio-Canada’s French Services’ programs, a letterbox is mandatory. For CBC/Radio-Canada’s English Services’ programs, most are down-converted using a center cut, while a letterbox is preferred for some programs. These current settings shall be used until otherwise advised.

720p59.94

.

1280 pixels

HD

720 lines

AFD =1111

720 pixels

SD

480 lines

AFD =1000

Figure 1 – Original full screen HD Image converted into an SD Image by means of a Center Cut.

Note:

The AFD=1111 for the original HD picture indicates that the image has a 4:3 area of essential information and can be center-cut during conversion to SD.

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Figure 2 – Original full screen HD Image converted into an SD Image by means of a Letterbox. Note 1: The AFD=1010 for the original HD picture in Figure 2 means that the program was shot for a full frame image with the entire picture area protected and has to be down-converted in letterbox format. Note 2: The AFD=1000 for the original HD picture in Figure 2 means that the program was shot for a full frame image with no picture area protection. This AFD value is often used as a default mode. When the source HD image is a pillarbox image (see Figure 3), the conversion to SD must be made by means of a center cut. This is to avoid the Postage Stamp effect.

720p59.94 1280 pixels

HD

720 lines

AFD =1001

720 pixels

SD AFD =1000

480 lines

Figure 3 – Original HD Image in Pillarbox mode converted into a SD Image by means of a Center Cut. 5.2.4.

The converter must perform an automatic aspect ratio conversion using the active format (AFD) information associated with each HD image provided at its input, as described in the SMPTE 2016-1 standard. The AFD is extracted from the vertical interval (VANC) of the HD-SDI interfacing signal, as described in the SMPTE 2016-3 standard. Each image has its own AFD; the aspect ratio

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conversion shall be applied immediately and only to the image following the passage of the AFD value in the vertical interval (frame accurate). The AFD value corresponding to the new aspect-ratio-converted image shall be inserted in the vertical ancillary data space of the SD-SDI interfacing signal at the converter output. Table 2 shows the AFD values of the HD signals provided by CBC/Radio-Canada and the AFD values that must be inserted automatically by the converter in the SD-SDI signals. Table 2 – Summary of Required Aspect Ratio Conversions

French Network AFD at the Converter HD Input Full Screen Image Full Screen Image Pillar Box Image

1010 1000 1001

AFD at the Converter SD Output 1010 1010 1000

Letter Box Image Letter Box Image Center Cut Image

Fig. 2 Fig. 2 Fig. 3

English Network AFD at the Converter HD Input Full Screen Image Full Screen Image Pillar Box Image

1111 1010 1001

AFD at the Converter SD Output 1000 1010 1000

Center Cut Image Letter Box Image Center Cut Image

Fig. 1 Fig. 2 Fig. 3

5.2.5.

As the HD-to-SD converter may not perform an exact conversion to the 4:3 aspect ratio, the geometrical distortion of the converted image shall not exceed 2%.

5.2.6.

Data shall be closed-captioned as per the EIA-608 and EIA-708 standards. At the converter input, the EIA-608 subtitle data is encapsulated in the EIA-708 data stream and inserted in the vertical interval of the HD-SDI interfacing signal, as described in the SMPTE 334M standard. The converter must extract the EIA608 data and insert it in the vertical interval of the SD-SDI interfacing signal.

5.2.7.

Data allowing program content ratings (violence, sex, adult language, etc.) are contained in the XDS data packet defined in the EIA-608 standard and inserted in the vertical interval of the SD-SDI interfacing signal, as described in section 5.2.6.

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Technical Specifications for High Definition (HD) TV Interconnection to BDUs and Down-conversion to Standard Definition (SD)

5.3.

Video Signal and Data Available at the Converter Output

5.3.1.

Interfacing Signal: SD-SDI at 270 Mbps as per the SMPTE 259M-C standard.

5.3.2.

Format: 480i59.94 as per the SMPTE 125M standard.

5.3.3.

Closed-captioned data as per the EIA-608 standard.

5.3.4.

Program content rating data as per the EIA-608 standard.

5.3.5.

Active Format Description (AFD): Data identifying the active SD image after aspect ratio conversion.

5.4.

Audio Signals Available at the Converter Input

5.4.1.

Main Audio: metadata.

5.4.2.

Described Video (DV): AES mono or AES dual mono, or AES stereo.

5.4.3.

Transport: The AC-3 audio signal is multiplexed with the video signal and inserted into audio channel 1 of the HD-SDI interface. If the audio signal used to describe video is provided, the AES mono or AES stereo signals are inserted into audio channel 2 of the HD-SDI interface. Audio channels multiplexing with video on SD-SDI and HD-SDI interfaces are defined in the SMPTE 272M and SMPTE 299M standards respectively.

5.5.

Audio Signal Processing

5.5.1.

AC-3 encoded (5.1) and Described Video (AES mono or AES stereo) signals are de-multiplexed from the HD-SDI interfacing signal. A downmix is made from the 5.1 audio channels to obtain Lo/Ro or occasionally Lt/Rt stereo signals, as described in the ATSC A/52 standard. These stereo and Described Video signals shall be re-synchronized before multiplexing them with the video signal on the SD-SDI interface at the converter output.

AC-3 encoded 5.1 audio channels with corresponding AC-3

The dialnorm value is part of the AC-3 metadata and indicates the measure of the loudness level. CBC/Radio-Canada’s standard for the dialnorm value is –24 dBFS and follows the ATSC A/85 Recommended Practice. AC-3 audio signals must not be decoded and later re-encoded in order to avoid significant degradation. AC-3 metadata must not be modified before distribution in order to preserve the loudness level. When a stereo downmix is made from an AC-3 signal, the program dynamic range may exceed 10 dB above the alignment level. In this case, the appropriate dynamic range setting (RF mode - film standard) must be selected in the AC-3 metadata stream.

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5.5.2.

Audio/video signals synchronization must be maintained during conversion. Automatic compensation of the delay introduced by the video signal processing must be made in order to obtain a perfect and constant synchronization between audio and video signals throughout the program. The maximum tolerable misalignment of sound and picture brought by the converter shall be less than +/- 5 ms.

5.6.

Audio Signals Available at the Converter Output

5.6.1.

Main Audio: Downmix Lo/Ro or occasionally Lt/Rt stereo signals inserted in Audio Channel 1 of the SD-SDI interface.

5.6.2.

Described Video: AES mono or AES stereo signals inserted in Audio Channel 2 of the SD-SDI interface.

6.

ACKNOWLEDGMENTS This document was written with the collaboration of various departments within CBC/Radio-Canada. We acknowledge the valuable input of the members of the working group: John C. Lee

Executive Director, Media Technology Services

Paul Munson

Director, Media Networks Engineering, Media Technology Services

Anthony Caruso

Director, New Broadcast Technologies, Media Technology Services

Jeff Vella

Director, Broadcast Engineering - Toronto

Pierre Marion

Director, Ingénierie Médias - Montréal

Martin Marcotte

Director, CBC Transmission, Media Technology Services

Adam Vulic

Supervising Engineer, Broadcast Engineering - Toronto

Marc Landry

Manager, Presentation Distribution and Quality Control, English Network Presentation

Laura Boorman

TV Master Control Technician, TPC Broadcast Services Television Master Control

Pierre Bourdeau

Supervisor, Master Control Montreal, Productions

Guy Bouchard

Senior Manager, New Broadcast Technologies, Media Technology Services

Félix Poulin

Engineer, New Broadcast Technologies, Media Technology Services

Michel Poulin

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