I am new to Arduino. Can I combine Arduino UNO and MEGA in 1 project? Arduino UNO is for audio output and MEGA for LCD display. If I am wrong, is there any ideas how do combine both LCD display and audio output in one microcontroller?
When you want to transport 8 people to a festival you can either use two cars and have 4 in each car, or you can get a minibus and have everyone together in one vehicle. It's often simpler to get a minibus, though hiring one may be outside your budget, so two cars is quite often the norm. The tricky part is to set up some form of communication between the drivers so they can both get to the same place at the same time and find each other.
It is exactly the same with microcontrollers (which the Arduino basically is). You can use one big powerful microcontroller to do everything, or you can split your task between a number of smaller microcontrollers. The tricky part is setting up some form of communication between them so that they can all coordinate what they are doing. Bigger microcontrollers can be more expensive though, and if you already have a couple of Arduinos at your disposal then connecting them together and sharing out different parts of your project to them is a good way of going.
Communicating between the Arduinos can be done in a number of ways, depending on how many Arduinos you are connecting, what kind of data there is going between them, etc. One common method which is well documented is to use I2C (Wire.h) to communicate. This is often chosen because it uses just two wires. For higher speed communication SPI is a good choice, but it requires more pins (4 for bi-directional communication). Of course, you can also connect them together using the UARTs, but on the smaller chips (such as the ATMega328P you get on the Arduino Uno) you only get one UART and that is used for programming, so using that for other things gets tricky.
I think you can manage to find a display that uses only a few pins, like Adafruit 2.2 TFT which has a 3-pins SPI communication. Then you have a lot of pins left to connect for example an audio shield.
I think this could be done on a single Arduino, you'll just have to find an Arduino board compatible with both audio and video systems you choose.
I only wonder if the audio playing would be suffering from screen refresh if both communications are in SPI.