[Live-devel] Detecting/Notifying on new multicast media

[Brian Marete]

On Thu, Oct 16, 2008 at 12:29 AM, Ross Finlayson <finlayson at live555.com> wrote:
>
>> I am writing a streaming application with live555, both on the server
>> and client ends. I will be using live555 to mulitcast MPEG2 transport
>> streams over RTP to the clients. Periodically, the server will stop
>> multicasting the current file and switch to a new one, sending it to
>> the same multicast address and port to which the previous TS was being
>> sent.
>>
>> Now, obviously, the second TS may defer in parameters from the 1st TS.
>> For example, the picture size could be different, or it could contain
>> a different video codec. I am thinking that the decoder on the client
>> end will need, somehow, to know of this change. Are there any
>> facilities in live555, the TS protocol or the RTP protocol that would
>> help with this.
>
> No, because the RTP payload format for Transport Stream data is extremely
> simple: RTP packets contain just the Transport Stream data (in groups of
> 188-byte transport 'packets'), with no extra RTP-specific parameters.  In
> other words, you don't do anything extra to our RTSP/RTP/RTCP code to stream
> your 'joined' Transport Stream data; instead, all of the information that a
> client's decoder requires needs to be in the Transport Stream data itself.
>
> Fortunately, though, the Transport Stream header (inside the Transport
> Stream data itself - independent of RTP) includes a 1-bit
> "discontinuity_indicator" that you can use to indicate - to a receiver -
> that a Transport Stream 'join' has taken place.  (See the ISO-IEC
> specification for Transport Streams: ISO-IEC 13818-1, section 2.4.3.5.)

Thanks.

-- 
B. Gitonga Marete
Tel: +254-722-151-590