[Live-devel] green screen at the start of MPEG4 stream reception

[Shiva Shankar N]

Hi Ross,

*" To avoid this, use unicast streaming, using "testOnDemandRTSPServer", or
"live555MediaServer". *"

please can you explain us how different is *"testOnDemandRTSPServer", or
"live555MediaServer"  *with *testMPEG4VideoStreamer   *in using to  reduce
or avoid green screen.

I have given below the reason for this green screen and i think it cannot be
avoided. If i am wrong let know.

It has so happen that session with server has started after  Key frame
(I-frame)  is sent & he as missed it . When the session starts it will be
downloading only p-frame without Key-frames in which case there is No
reference frame for these P-frame to do motion compensation and this green
screen is nothing but motion estimation. You can reduce this green screen
period by reducing the GOV(group of videos) or GOP (group of picture) size
at the server side in camera settings.

P.S : GOP or GOV -  Number of P-frames between 2 consecutive I-frames(Key
frames).

with regards
shiv




On Fri, Aug 15, 2008 at 11:51 AM, Ross Finlayson <finlayson at live555.com>wrote:

> While receiving and playing back MPEG4 encoded streams using VLC, the first
>> few frames happen to be green screen. The message window shows the following
>> error
>> "ffmpeg warning: warning: first frame is no keyframe". The playback gets
>> back to normal state on the arrival on next MPEG4 keyframe. I observed this
>> with testMPEG4VideoStreamer.exe. and the issue is consistent with repeated
>> runs.
>> Is it because client didn't get first few frames on MPEG4 stream?
>>
>
> Yes, probably.
>
>   where do the frames gets dropped?
>>
>
> Remember that "testMPEG4VideoStreamer" is a *multicast* application - it
> just sends the data to a multicast group, regardless of how many clients
> have subscribed to the group.  Therefore, any data that it sends before the
> client runs (and subscribes to the group) will be lost.
>
> To avoid this, use unicast streaming, using "testOnDemandRTSPServer", or
> "live555MediaServer".
> --
>
> Ross Finlayson
> Live Networks, Inc.
> http://www.live555.com/
>
> _______________________________________________
> live-devel mailing list
> live-devel at lists.live555.com
> http://lists.live555.com/mailman/listinfo/live-devel
>
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