[Live-devel] SAP announcements and the live555 library in VLC (multiple media ports please)

[John Blyth]

Thanks Ross,

it is not a problem decoding the SDP file and the corresponding stream
- VLC and QuicktimePlayer7 all do this and will display the rtsp
stream from the information encoded in the SDP file. {The openrtsp
does not have a SAP interpreting function?}

The problem we have been experiencing is decoding the SAP announcement
with the SDP information embedded inside it. VLC does interpret SAP
announcements, but not SAP announcements with multiple media lines.
The "messages" output from VLC implies that it is a live555 library
function {used to decode the SAP announce}

here's a line that one sees often in that messages window...

"sap debug: Multiple media ports not supported -> live555"

If you forgive me (in advance) the VLC developer said " I do not know
what live555 does internally. This is not developed by the VideoLAN
project."  But it seemed to imply that live555 library was used by VLC
for parsing SAP, but I may? be wrong.   The debug message was the only
clue I had for the observed behaviour.

What I was hoping to achieve, is to find out if live555 is used for
decoding SAP announcements in VLC, & does support multiple media
ports, why that is not being included or recognised in VLC - a bit of
a tricky situation for a third party user outside of the development
teams of videolan and live555, & get it fixed.

On Fri, Mar 4, 2011 at 2:43 AM, Ross Finlayson <finlayson at live555.com> wrote:
>> the live555 library is used by VLC.  VLC can decode SAP announcements
>> to make it easy for end users to access playlists via SAP announce and
>> it appears that the live555 library is used to decode the SAP
>> announcements.
>
> Yes, but not exclusively (I think).  I.e., I think that sometimes VLC uses a
> separate mechanism - not using our libraries - to parse/decode SAP
> announcements.  I'm not sure about this, though, because VLC is not our
> software, and I'm not sure how it works internally.
>
>
>>  But VLC will not decode properly formed SAP
>> announcements where there is more than one media line. It appears that
>> this is a function of the live555 library
>
>> Now I assume the live555 library was written with the assumption that
>> the main media being used was multiplexed MPEG-TS with one port set
>> only, and so one connection entry; one media file is all that it
>
> Incorrect.  Our library has *always* been able to parse/handle SDP
> announcements that have multiple "m=" lines (e.g., one "m=" for audio; one
> "m=" for video).
>
> If your stream is accessible via a "rtsp://" URL, then you can verify this
> using our "openRTSP" RTSP client application.  (Unlike VLC, openRTSP *is*
> our software.)
>
> So, please try opening our stream using "openRTSP", and let us know if you
> have any problems with this.
> --
>
> Ross Finlayson
> Live Networks, Inc.
> http://www.live555.com/
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