[vlc-devel] Help about GET_PARAMETERS

Glen Gray slaine at slaine.org
Thu Jun 9 12:51:46 CEST 2011

On 9 Jun 2011, at 03:31, chenhui zhang wrote:

> Hi all,
>         I'm testing our device as a media server and use VLC as the client. When in RTP over TCP mode, vlc can't play the stream. I capture the tcp packet,
> found that the rtsp is OK and when send the media data to vlc over rtsp, it seems vlc doesn't recv the data because the TCP windows size of vlc side is down
> to zero and never recover. I also found there is a GET_PARAMETERS message from vlc to device and device reply an empty response after the PLAY method.
> When I remove the GET_PARAMETERS from the OPTION response of device and try again, it's OK. So I doubt the problem has relations to GET_PARAMETERS.
> I have search this on Google and there are some information about this but no clearly answer of it. VLC used GET_PARAMETERS as a ping to device, but when I
> send GET_PARAMETERS response to vlc, why it still can't play?

The GET_PARAMETERS should only trigger if the RTSP SETUP response includes a timeout value. If a timeout is there, VLC will send an empty GET_PARAMETERS message as a keep alive method for the stream. Say for example you paused the stream for > timeout, you don't want the session torn down. There are other methods for doing keep alive, like RTCP "RR" messages.

Glen Gray
<slaine at slaine.org>

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