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I want to write an app in java that lets two clients talk via webcam. The way it works is both clients connect to a webcam that takes pictures at a specified frame-rate (20 per second maybe) then reduced the size and resolution, then sends it to the other client via a UDP packet. My question is - should I send every picture in its own Datagram Packet? I've read that they can only hold half a kilobyte at most so should every pic be cut down that much? Or should I have it split up into several Packets?

Tyler Petrochko
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  • UDP datagrams can transmit up to 64K. However, depending on your lower layer-2 (Ethernet), this datagram will be split in many IP fragments. Fragmented packets will be assembled back at the receiving host, but if one of the fragment is lost, all the UDP packet is lost. – jfg956 Aug 08 '11 at 17:13

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Are you sure you want to transmit whole images, instead of using an algorithm / codec that transfers only what needs to be updated?

If you choose the second option you can take some ideas from this previous question and a already used and tested library for the purpose. I believe i'd go with VLC java bindings if i had to do it. You should evaluate what is the best codec for your specific purpose (bitrates, quality, etc).

If you nevertheless want to transmit images i'd suggest you break them down into udp datagrams, remember that they should be somehow numbered/tagged so that the client can reconstruct the image as packets come (they won't necessarily come in the same order you send them), also you need to think what the client needs to do when some of the packets fails to arrive (discard the image, request previous packet, etc.).

One last thought, the udp datagram max size might not be the best option as well, your server-client should perhaps implement a algorithm and negotiate the udp frame size depending on the speed of the transmission.

Community
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Bruno Flávio
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What you should be doing is encoding a video stream. Leave the network layer alone, let it do fragmenting for you.

Also, if you are sending video over UDP, you will likely want to throw in a keyframe every 2 seconds or so.

Do not send each frame as its own image. Use a video compressor.

Brad
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