FOX NETWORK

To recap, audio and video are now distributed to FOX affiliates by sending a complete 19.39 Mbps ATSC transport stream (see A/53b) in the same manner as PBS does today, with the exception that the network has furnished transport stream splicers for all affiliate stations. The network is also providing a full-time 5.1 channel audio feed during prime time. This approach allowed the network to begin the 2004 fall season with most all of its affiliate stations broadcasting HD video and 5.1 channel audio, while maintaining the ability to switch in local programming. However, the onus is now heavily on the local broadcaster to match the quality and consistency of the network delivered 5.1 channel content.

Adding local content can be done in several different ways. The two most common are decoding the transport stream into baseband audio and video and splicing a local transport stream together with the network transport stream. Each has advantages and drawbacks and both are presented below.

BASEBAND APPROACH

In the case of a baseband decode, the transport stream is decoded and the audio and video can simply appear as another source in master control, selectable in much the same way as current network feeds. The main problem with this approach is a potential loss of audio and video quality. With modern compression equipment, the results can be surprisingly good but you never know exactly how close to the edge of artifacts you might get.

KEY POINTS

• Standard IRD (Integrated Receiver/Decoder) can be used to decode audio and video
• Baseband audio and video signals can be treated as another HD source
• A separate Dolby Digital (AC-3) decoder is strongly recommended
• Potential negative effects on audio quality due to decode/re-encode
• Keep all codecs at maximum permissible bitrate (448 kbps)
• Adding a Linear Acoustic OCTiMAX 5.1 at the affiliate station can protect audio from incorrect or missing metadata and local content can be selectively upmixed to match network sound sources

TRANSPORT STREAM SPLICING APPROACH

Relatively new to terrestrial broadcast, transport stream splicing has evolved rapidly in the cable and satellite worlds to allow insertion of local or targeted programming and commercials. Today's products have not only dropped substantially in price, but also allow some operations to occur to the compressed bitstreams without requiring a decode/re-encode.

KEY POINTS

• Highest quality as signals are encoded only one time
• Allows insertion of local video bugs in compressed domain
• Audio must still be decoded then re-encoded for local operations
• A Linear Acoustic OCTiMAX 5.1 could be placed just prior to Dolby Digital (AC-3) encoder to help local 2-channel audio better match network 5.1 audio pre- and post-splice

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