Subject: [AVT] ‏‏RE: avt Digest, Vol 39, Issue 20

From: Amit Yedidia <[email-masked]>
Date: Sat, 14 Jul 2007 22:18:17 +0300

There are basicly two methods. one with RTCP and the one without.
1. without RTCP - you must assume that the two streams (audio and video) were started at the same time.
now for example we are using MPEG4 (90khz) for video and AMR-NB (8Khz).
lets mark the first Video RTP timestamp as RTPv_base and the first Audio RTP timestamp as RTPa_base.
for every video rtp packet ( i ) that arrived its presentation time in msec is:
Tvid = (RTPv_i -RTPv_base)/90
and the same for audio:
Taud = (RTPa_i -RTPa_base)/8
2. when you have RTCP on both streams you can get an additional info on both strems in the sender report, which allow you to sync the streams even if they not started in the same time.
for each streams you get a timestamp and an NTP timestamp. The NTP timestamp is common (from the same source) to both streams, so yo can make adjustments.
diff = (NTPaud_rtcp-NTPvid_rtcp) - (RTPaud_rtcp/8 -RTPvid_rtcp/90)

Tvid = (RTPv_i -RTPv_base)/90
Taud = (RTPa_i -RTPa_base)/8 - diff

hope it helps

Amit Yeidida
AudioCodes Ltd.

________________________________________
‏‏מאת: [email-masked] [[email-masked]]
‏‏נשלח: ‏‏יום שישי 13 יולי 2007 19:00
‏‏אל: [email-masked]
‏‏נושא: avt Digest, Vol 39, Issue 20

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Today's Topics:

   1. I-D ACTION:draft-ietf-avt-rtp-svc-02.txt
      ([email-masked])
   2. Synchronisation of Audio and Video (Vinod Madhav Joshi)

----------------------------------------------------------------------

Message: 1
Date: Thu, 12 Jul 2007 12:15:12 -0400
From: [email-masked]
Subject: [AVT] I-D ACTION:draft-ietf-avt-rtp-svc-02.txt
To: [email-masked]
Cc: [email-masked]
Message-ID: <[email-masked]>
Content-Type: text/plain; charset="us-ascii"

A New Internet-Draft is available from the on-line Internet-Drafts
directories.
This draft is a work item of the Audio/Video Transport Working Group of the IETF.

        Title           : RTP Payload Format for SVC Video
        Author(s)       : S. Wenger, et al.
        Filename        : draft-ietf-avt-rtp-svc-02.txt
        Pages           : 0
        Date            : 2007-7-12

This memo describes an RTP payload format for the scalable extension
   of the ITU-T Recommendation H.264 video codec which is technically
   identical to ISO/IEC International Standard 14496-10.  The RTP
   payload format allows for packetization of one or more Network
   Abstraction Layer (NAL) units, produced by the video encoder, in
   each RTP payload.  The payload format has wide applicability, such
   as low bit-rate conversational, Internet video streaming, or high
   bit-rate entertainment quality video.

A URL for this Internet-Draft is:
http://www.ietf.org/internet-drafts/draft-ietf-avt-rtp-svc-02.txt

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Message: 2
Date: Fri, 13 Jul 2007 10:39:21 +0530
From: Vinod Madhav Joshi <[email-masked]>
Subject: [AVT] Synchronisation of Audio and Video
To: <[email-masked]>
Message-ID: <[email-masked]>
Content-Type: text/plain;       charset="iso-8859-1"

Hi all,

   We are receiving MPEG2 demuxed elementary audio and video streams
   from streaming server on the set top box.
   The source for audio and video is the same.
   I want to know how to synchronise this audio and video data using
   RTP timestamps.
   Timestamp does not increase monitonically as the data was sampled.
   So how to generate Presentation Timestamps for audio and video?

   Please help me.

   Thank You.

------------------------------

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End of avt Digest, Vol 39, Issue 20
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