[vlc-devel] [PATCH 1/1] Supporting ONVIF PRofile-G recording playback

David R. Robison david.robison at openroadsconsulting.com
Tue Aug 5 19:50:10 CEST 2014

What I am attempting to to is to allow VLC to be used to play recorded 
video according to the ONVIF Streaming Specification 2.1. We currently 
embed VLC in our application. What I want to do is to use the 
medial_player handle and set the recorded playback start/end time. 
According to the ONVIF Specification, when using RTSP to play recorded 
video, the start/end times are specified in absolute time and sent to 
the video device using the "range: clock" tag. Currently I can use the 
vlc library to set the time and length but there is no current way 
within the live555 module to tell if the time is in NPT time or CLOCK 
time (e.g. unix seconds). At this point I am not so concerned with 
getting the current playing time but setting the limits for recorded 
playback. Also, initially I do not need to implement this in the VLC GUI 
since I already have an application that VLC in embedded in, as long as 
there is a way via the VLC library to set the start/end time. Sorry for 
not being clear before, hope this clarifies the issue. David

David R Robison
Open Roads Consulting, Inc.
103 Watson Road, Chesapeake, VA 23320
phone: (757) 546-3401
e-mail: david.robison at openroadsconsulting.com
web: http://openroadsconsulting.com
blog: http://therobe.blogspot.com
book: http://www.xulonpress.com/bookstore/bookdetail.php?PB_ISBN=9781597816526

On 8/5/2014 1:39 PM, Ross Finlayson wrote:
> At this point perhaps it's worth stepping back and asking: Where do 
> these 'absolute' times come from?  I.e., What are you doing (or 
> planning on doing) in VLC to get these 'absolute' times?
> If you're planning on getting these times simply by 'seeking' using 
> VLC's GUI (i.e., using its slider), then those are *not* absolute 
> times - they are relative times.  That's explicitly what 'npt' 
> ("Normal Play Time") means (see RFC 2326, section 3.6, paragraph 3). 
>  Therefore, if you're getting these times only by 'seeking' using 
> VLC's GUI, then "range: npt" strings are *exactly* what you want - and 
> therefore you should not be considering making *any* changes to VLC.
> Note that (quoting from RFC 2326, section 10.5, final paragraph) "A 
> media server only supporting playback MUST support the npt format and 
> MAY support the clock and smpte formats".  Therefore, if your server 
> does not support "range: npt" strings, then it is *not* standards 
> compliant, and VLC (nor any other media player client) is under no 
> obligation to support it.  Note that the Internet standard here is RFC 
> 2326 (IETF), not 'ONVIF'.  ('ONVIF' is an 'industry consortium', not a 
> standards organization.)
> If, on the other hand, you're planning on getting these 'absolute' 
> times in some way other than by using VLC's GUI slider, then 
> presumably you can arrange to generate the appropriate (ISO 8601 
> format) string then, assign it to some "char*" variable, and modify 
> VLC's "live555" access module to check whether that variable is 
> non-NULL - and then call the appropriate version of "sendPlayCommand()".
> Ross Finlayson
> Live Networks, Inc.
> http://www.live555.com/
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