Vfrdtyky

Always when I find some articles or videos are talking about stream they're necessairly talking about serialization?
what is the relation between those? or to be specific,
Could we say that the data stream always needs serialization or could we find some data stream without serialization?

Firstly, it useful to have a reminder of serial vs parallel communication: if we take a simple example of transmitting a byte, in the parallel case all 8 bits are sent at the same time and in the serial case the 8 bits are sent one by one and the byte built again on the receiving side.

For your video domain example, If you imagine a frame of a video as being a large collection of bytes, lets say 720 by 1280 pixels and each pixel is represented by a byte, then we need 921,600 bytes to represent the frame.

If you are streaming the video you need to send each frame (plus overhead which we'll ignore here for simplicity) from the server to the client device, hence you need to send the 921,600 bytes for each frame.

If you had a very (very!) large parallel connections that could transmit 921,600 bytes in parallel between the server and the client in a single communication then this would be easy to understand.

However, this is almost always not the case, even for much smaller data structures, so serialisation is the name generally given to the process of taking the 921,600 bytes and breaking them down into the size which you can transmit - and that size is often one bit at a time.

Generally a video will be broken down into packets and the packets transmitted to the client. The packets themselves are just collections of bytes also and if the connection allows only a single bit of information to be transmitted at a time, then the packet needs to be broken down and sent 'serially' one bit at a time.

To complicate things, as is commonly the case in computer science and communications, the terms can mean different things in different contexts.

For example you may see it mentioned that you can either stream or 'serialise an object' in some client server communication. What this generally means is that you can either send the raw data 'stream' and let the client be responsible for how to interpret it, or you can use a framework or underlying mechanism which will take an object, convert it into a format that can be transmitted serially, and then reconstruct it on the other end and give it to the client. In fact the actually communication is serial in both cases (if it is using a serial communication channel) so the terms are being used in a different way here.