MJPEG player with UDP server using Synapse
lazarus / 38-Networking and Web Programming

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lenuisible · 2013-05-22 15:52

Hi guys,

I have what should be an easy program to write with Lazarus and
Synapse, but I can't figure out what receive method I should use.

Let me describe the context :

- I have a camera which send a UDP stream, which is basically a MJPEG
video stream composed by approximately 10 JPEG images per second of
25kB each
- each datagram starts with 4 bytes giving its size (header+ JPEG)
- The 16th byte gives the position of the starting of the JPEG (FFD8)
- The end of the datagram is also the end of the JPEG (FFD9)

So what I try to achieve :
- use a UDP socket to receive the datagrams
- find out the size of every datagrams
- cut the interesting part (the JPG)
- display them

I've looked at the UDP Server example on the synapse howto
(http://www.synapse.ararat.cz/doku.php/public:howto:udpserver), but
I'm a bit lost identifying what method I should use.

To be a bit more precise :

- is there an existing function to get a datagram size ?
- How could I define a buffer big enough to receive 25KB ? I've
thought using the RecvBuffer function (http://synapse.ararat.cz/doc/he
lp/blcksock.TBlockSocket.html#RecvBuffer), but I don't understand how
to define a 25KB "Tmemory" buffer ...

- Which receive method I could use to split the datagram without
having to use string ? I may be wrong, but I'm afraid working with
string will be too slow to handle a 250KBps stream (and the RecvPacket
seems to be limited to 8192 char lines, even if I use ansistring)

Thanks in advance for your help,

Rgds