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Thread: Audio/Video Sync issues

  1. #1
    Join Date
    Mar 2013
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    Default Audio/Video Sync issues

    Hi,

    We are facing A/V sync issue in live streaming from a RTP source via Wowza Media Server(v3.1.1 build1479), where sometimes audio(AAC) is ahead/behind video(H264).
    AVSyncMethod we are using is senderreport and configured in conf/[application]/Application.xml. Also we have not enabled rtpResyncAudioVideoOnSR property and hence Wowza should sync using first RTCP sender report for video/audio streams.

    We have following queries with above configuration set:
    1. Does Wowza use the very first Sender Report and ignores all the reports coming after this
    2. Or does it use Sender report when it receives first H264 SPS packet, which may not be the very first Sender report
    3. Does Wowza expect RTP source to send both Audio and Video sender reports at the same time
    4. Is there a minimum number of Audio and Video RTP packets expected in Wowza receive buffer before receiving first RTCP Sender Report
    5. After receiving first Sender report how does Wowza media server syncs Audio/Video streams, does it look at RTP timestamps in media packets

    Thanks,
    Hitesh

  2. #2
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    Mar 2013
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    Default

    Wowza Support,

    We are kind of blocked on debugging the A/V sync issue, could you please help us by answering above queries.

    Thanks,
    Hitesh

  3. #3
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    Dec 2007
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    Default

    Hitesh,

    Sorry, I should have mentioned that I forwarded your post yesterday to get the authoritative answer. I'm not sure when that will come back because of post NAB travel and end of week.

    Richard

  4. #4
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    Default

    Hi Richard,

    Did you get any update on our queries above?

    Thanks,
    Hitesh

  5. #5
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    Not so far. The short answer to most a/v sync issues is that it has to be fixed in the encoder. Have you looked at this article for debugging audio timecodes

    http://www.wowza.com/forums/content....-packetization

    Richard

  6. #6
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    Default

    Yes, I have tried that but didn't see any of those logs on the wowza console.

    Hitesh

  7. #7
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    You have to add "cupertinostreamingpacketizer" to the Application.xml /Streams /LiveStreamPacketizers, and add one of those properties, then turn the stream on, then check the logs.

    Richard

  8. #8
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    Default

    Yes I did follow steps mentioned above but there weren't those logs in the console output.

  9. #9
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    Default

    Here are the answers to the above questions from Wowza Engineering (Charlie):


    1. Does Wowza use the very first Sender Report and ignores all the reports coming after this?

    Yes, by default we only look at the first video and audio SR report to sync the streams. You can instruct Wowza Server to
    look at subsequent SR reports by adding this property to you RTP/Properties in conf/[application]/Application.xml:

    <Property>
    <Name>rtpResyncAudioVideoOnSR</Name>
    <Name>true</Name>
    <Type>Boolean</Type>
    </Property>

    2. Or does it use Sender report when it receives first H264 SPS packet, which may not be the very first Sender report?

    We use sender report.

    3. Does Wowza expect RTP source to send both Audio and Video sender reports at the same time?

    No, we can handle these out of sync and not at the same time.

    4. Is there a minimum number of Audio and Video RTP packets expected in Wowza receive buffer before receiving first RTCP Sender Report

    No, we can handle the SR reports before we receive any video or audio packets. We are also Ok receiving them after some number of
    audio and video packets.

    5. After receiving first Sender report how does Wowza media server syncs Audio/Video streams, does it look at RTP timestamps in media packets

    Yes, we look at the RTP timestamps and use these values to relate them to the wall clock based on the SR reports.

    -rl

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