LatAm Supp LatAm | Page 13

Advantages: l Subtitle format conversion available: - Teletext to DVB - Imitext to DVB Disadvantages: l Viewers must have suitable decoders. Advantages: l No separate subtitle inserter required. l Suitable for situations where the video encoding standard needs to be changed. l No special subtitle decoder required by viewers. Disadvantages: l The video must be decoded and recoded: - Cost of equipment - Loss of video quality - Delay in the video path Open Subtitles - using a subtitle inserter at a headend. Closed subtitles for a range of languages are supplied by the original broadcaster in a suitable format such as Teletext, DVB bitmap or Imitext. At each headend a professional receiver/decoder (IRD) decodes the video and a separate subtitle inserter unit (Polistream) adds open subtitles into the video. The resulting combined video with open subtitles is then re-encoded for broadcast. The subtitle language is selected from those supplied by the original broadcaster. Advantages: l High quality subtitle text. l Animated or static logos. l Other localisation components can also be added such as tickers and clocks. l Suitable for situations where the video encoding standard needs to be changed. Disadvantages: l The video must be decoded and recoded: - Cost of equipment; - Loss of video quality - Delay in the video path Open Subtitles - using an MPEG2 subtitle inserter at a headend. Closed subtitles for a range of languages are supplied by the original broadcaster in a suitable format such as Teletext, DVB bitmap or Imitext. At each headend a professional receiver (IRD) generates a decrypted compressed transport stream (ASI) and a separate MPEG-2 subtitle inserter unit (Polistream) adds open subtitles into the compressed video. The subtitle language is selected from those supplied by the original broadcaster. Advantages: l The video signal is not decoded and stays in MPEG-2 format. l Multiple video channels can be modified in a single unit. l Static logos can be added. l Minimal through delay. l Cost saving on decoders, encoders and multiplexes. l The original broadcaster maintains control of the final video image. Disadvantages: l Short through delay (approx. 800mS). l Currently only available for MPEG-2 streams. l Small increase in video bit rate. Closed Subtitles - with video format conversion Closed subtitles for a range of languages are supplied by the original broadcaster in a suitable format such as Teletext, DVB bitmap, Imitext or SCTE 27 (EIA 608 &708) closed caption. In this case the subtitles are delivered as closed subtitles and the viewer, with a suitable receiver or STB, can select which language subtitles they wish to see. This configuration applies when the video format needs to be converted (e.g. NTSC to PAL, HD to SD, MPEG-2 to MPEG-4) at the headend. At each headend a professional receiver/ decoder (IRD) decodes the video. Subtitle data is removed from the broadcast signal and then re-inserted into the recoded output (Polistream). A delay is added to the subtitle stream to match the delay in the video path. Closed Subtitles - with re- multiplexing and subtitle transcoding Closed subtitles for a range of languages are supplied by the original broadcaster in a suitable format such as Teletext, DVB bitmap, Imitext or SCTE 27 (EIA 608) closed captions. In this case the subtitles are delivered as closed subtitles and the viewer, with a suitable receiver or STB, can select which language subtitles they wish to see. No video format conversion is required. At each headend a professional receiver generates a transport stream (ASI) which is then re-multiplexed with other services to produce the required output multiplex(es). If required, subtitle format conversion can be performed at this point (Polistream): For example to convert from Teletext to DVB Bitmapped subtitles. Advantages: l Cost saving on decoders, encoders and multiplexes. l The video signal is not decoded and stays in MPEG-2 format. l Subtitle format conversion available: - Teletext to DVB - Imitext to DVB • Lower cost. Delays and Content Control Where: l channels are rebroadcast there is often a requirement to delay the service or to exercise some degree of control over the content of the channel. l the video signal stays in the compressed domain as in points 3 and 5 (above) a delay can be added to the ASI transmission path. l the video signal is decoded to uncompressed video as in points 1, 2 and 4 (above) then any delay needs to be in the SDI (or HD-SDI) path, normally in a video server. Once uncompressed video is available then content control can be added. This allows video editing, splices and insertions with relatively short pass through delays of only 30-60 minutes. Screen can offer solutions for both delays and content control complete with subtitle support. LATAM Briefing 13