SLIDE 1
May 07, 2007 AVBTP task group
May 07, 1007 AVBTP task group 2
AVBTP Presentation Time May 07, 2007 AVBTP task group Life of an - - PowerPoint PPT Presentation
AVBTP Presentation Time May 07, 2007 AVBTP task group Life of an - - PowerPoint PPT Presentation
AVBTP Presentation Time May 07, 2007 AVBTP task group Life of an AVBTP stream May 07, 1007 AVBTP task group 2 Assumptions The Presentation Time has the following purposes: Reconstruction of the media clock Account for link
SLIDE 2
SLIDE 3
May 07, 1007 AVBTP task group 3
Assumptions
The Presentation Time has the following purposes:
Reconstruction of the media clock Account for link latency Possible Synchronization of streams
AVBTP Presentation time is only associated with a single AVBTP stream Presentation time is relative to the 802.1as clock
SLIDE 4
May 07, 1007 AVBTP task group 4
Real Time Audio
SLIDE 5
May 07, 1007 AVBTP task group 5
Real Time Audio
Ingress time is when the sample is sent to the AVBTP layer On an I2S interface this is a 802.1AS timestamp of the word clock transition for the received sample. Egress time is the Ingress time plus a delay constant
SLIDE 6
May 07, 1007 AVBTP task group 6
Stored Media
SLIDE 7
May 07, 1007 AVBTP task group 7
Stored Media
When samples are simply being read from a disk or other media there is no media clock. Simulated ingress times can be computed easily with access to the 802.1AS clock and the streams sample rate. Shaping of sample delivery will have to be done at some point as per 802.1Qav
SLIDE 8
May 07, 1007 AVBTP task group 8
I2S timing
SLIDE 9
May 07, 1007 AVBTP task group 9
AVBTP Streams in a Home Theater
Ethernet AVB Switch Stored Media (DVD) Rear Left Rear Right Front Right Front Center Front Left Subwoofer Video Surround Sound Decoder
SLIDE 10
May 07, 1007 AVBTP task group 10
AVBTP Streams in a Home Theater
Home Theater systems are going 7.2 (7 speakers, 2 subwoofers) 9 audio channels + 1 video channel Global audio delay (Lip Sync) can be adjusted by the user Delay for each audio channel can be adjusted by the user Typical setup involves placing a microphone at the listening position and have the surround processor auto set delays
SLIDE 11
May 07, 1007 AVBTP task group 11
Presentation Time Formats
Egress Time (30-64 bits)
Requires no math on the egress side Could be limited to 2 msecs or less
Ingress Time (64 bits) + offset (30 bits?)
Requires minor math on the egress side Offset would give recommended egress time, but will still allowing the receiver to align streams based on actual ingress time if desired.
Ingress Time (64 bits)
Requires some negotiated or default delta between ingress and egress Additional setup information required to be defined
SLIDE 12
May 07, 1007 AVBTP task group 12