1. HDTV Video and AC-3 Payload Formats Ladan Gharai (ladan@isi.edu) Allison Mankin (mankin@isi.edu) USC/ISI

2. Motivation HDTV formats are starting to be used in studio, distributions, broadcasts, and in high bandwidth nets –US commercial broadcasts of 1920x1080 as of 5/99 –Use of uncompressed - tradeoffs of decoding versus bandwidth; some very high resolution applications Bandwidths from 176 Mbps (SDTV 640x480 24P) to 1.49 Gbps (1920x1080 60I/30P) –Target bandwidths of digital broadcast - 19.4 Mbps digital cable - 39.1Mbps

3. HDTV over RTP US HDTV standardized by ATSC (Advanced Television Standards Committee) –www.atsc.org Europe’s HDTV standard is DVB –www.dvb.org Major differences –Terrestrial receiver technology (COFDM vs 8VSB) –DVB uses MPEG audio, ATSC uses AC-3 Dolby Others are using one of these, if using digital formats

4. RTP Payload for HDTV Video Streams draft-avt-hdtv-video-00.txt drafted, not yet submitted Compressed HDTV video mostly covered by RFC 2250 - MPEG-2 transport and MP@HL. DVB audio? Payload type issue for compressed –Some expectation that some HDTV decoders will break if handed an arbitrary MPEG-2 stream Uncompressed HDTV –Cover color sub-sampling of both 4:2:0 and 4:2:2 –Related to BT.656 (ITU-R) (RFC 2431), but BT.656 lacks 4.2.0 and only covers 525/625 lines (HDTV up to 1080 lines)

5. RTP Payload for AC-3 Audio Streams draft-avt-ac3-audio-00.txt drafted, not yet submitted. Place an integral number of sync frames per RTP packet Fragmentation needs to be handled - frame sizes at 48Khz range from 128-2560 bytes Sync frames must be reassembled prior to decoding, as decoder takes all or nothing –No dependency on other frames –AAC-like audio repair seems applicable

6. P: progressive scan I : interlaced scan

7. Dolby Digital AC-3 A digital compression algorithm from Dolby labs –Input: 1 to 6 PCM audio channels –Output: a serial bit stream with data rates of 32kbps to 640kbps Low bandwidth is achieved by encoding multiple channels as a single entity example: –6ch * 48kHz *18bits = 5.184Mbps AC-3 encoder 384kbps left right center left surround right surround low frequency effects

8. AC-3 Audio streams An AC-3 audio stream is a sequence of same size “sync frames” Each sync frame is an independent data unit, I.e. it does not need require any other data to be decoded an AC-3 decoder must be presented with the entire sync frame AB: Audio Block SI: synchronization information header BSI: bit stream information header CRC: cyclic error check SI BSI AB1AB2AB3AB0AB4AB5Auxcrc sync frame SI BSI 256 samples