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Thread: Video Artifacts Temporarily Appear After Seek

  1. #1

    Default Video Artifacts Temporarily Appear After Seek

    Right after a video seek over rtmp/rtmpe, visual artifacts appear for around eight seconds. Otherwise, the seek is instant. I don't think it's the media file's fault because the same file doesn't have this issue when I use it in a different Wowza installation in another network environment.

    Setting the seekTarget to "enhanced" fixes this problem, but I'd like to know if there's some other underlying issue I can check.

  2. #2

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    Hi,

    This is usually caused by a lack of keyframes within the source file and/or bandwidth which is close to that of the stream. When seeking Wowza needs to clear the current buffer to the client before seeking, so this may take longer than expected due to bandwidth constraints, and it may not always be to a keyframe thus you can get artifacts and only when the next keyframe arrives does the picture get fully reset.

    Andrew.

  3. #3

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    Quote Originally Posted by andrew_k View Post
    When seeking Wowza needs to clear the current buffer to the client before seeking ... and it may not always be to a keyframe thus you can get artifacts and only when the next keyframe arrives does the picture get fully reset.
    But if the seekTarget value is set to "keyFrame", then wouldn't the first content of the cleared buffer be a keyframe rather than a non-keyframe? I'd expect it to make the picture reset instead of causing artifacts.

    I'm also not sure how the "enhanced" seekTarget acts as a workaround to the lack of keyframes and/or bandwidth. It can't possibly speed up the buffer clearing, so I assume it has the same effect of increasing the amount of keyframes in the content by generating "ad-hoc" keyframes.

  4. #4

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    Hi,

    Although Wowza may seek to a keyframe it does depend on the delivery to the client. If the bandwidth to the client is limited, ie. near the bandwidth of the stream then Wowza does have to wait until the current buffer is flushed which may be causing the issue to the client.

    I do agree you would expect keyframe seeking to give a cleaner seek than enhanced, but it may be bandwidth issue rather than a seek issue. Enhanced seeking does take slightly longer (we are talking ms here) as it provides a more accurate position to the file so it may be that time which is allowing the buffer to clear before pushing new data to the client, so keeping everything nicely synced on the player.

    Andrew.

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