bitrate explanation?

[ReinisK]

Hey guys!
Can someone explain please what does bitrate really do in video? And what is the technical difference between, for example, a 40 mbit/s video and a 20 mbit/s video?

[1%]

http://en.wikipedia.org/wiki/Bit_rate

[ReinisK]

I looked into that wiki page, but still couldn't find the explanation (maybe I just missed it, I don't know). If we take a 40mbit/s video and cut the bitrate to 20, exactly which information gets cut in half? I want to that.

[ItsMeLenny]

You will lose visual quality.

At low bitrates videos can look very blocky.

[dmilligan]

exactly which information gets cut in half? I want to that.

http://en.wikipedia.org/wiki/Lossy_compression
http://en.wikipedia.org/wiki/Advanced_Video_Coding
http://en.wikipedia.org/wiki/Rate-distortion_theory

[Johng]

I was just thinking about this question. This is what my understanding is of Bit rate. Bit rate refers to 2 general functions. 1) how many bits the camera, etc. is going to record at a certain speed,which is linked to the Frame rate, to maintain a no drop out video stream at a set quality setting such as HD Vs SD. And 2) the more bits recorded per frame the more information about the scene is captured will in turn create a higher quality video. So, at a given constant frame rate how many bits are needed to be recorded at a given quality setting to maintain a no dropout video stream on my Canon 60d?
Others can chime in if I have something incorrect here with additional thoughts.
I feel the minimum bit rate to record Full HD no drop outs is 20 mbit on my camera. The camera can write up to 30 mbit. I tried the 4GB class 4 SD card that came with my Canon camera Kit. And that was way to slow to record video with out a lot of drop outs. I originally bought SanDisk 8GB 20mbit cards and in my tests that works. I prefer to find out what the actual bit rate write speed the card is designed for not the Class Rating. I don't see much if any quality difference myself between 20mbit and 30mbit. What ever maintains a no drop out video stream would probably work. I like to have the highest quality possible even if I can't tell the difference? So I use 45mbit SD cards. You would have to experiment by recording the same scene at different bit rates and compare side by side. Compression like that performed by a computer is a whole different topic.

John

Hey guys!
Can someone explain please what does bitrate really do in video? And what is the technical difference between, for example, a 40 mbit/s video and a 20 mbit/s video?

[chmee]

the are more bitrate-problems as you see. on one hand its the bitrate (dataamount) of the video, on the other hand the bitrate (speed) of the card and the sd-card-slot. first you should know how fast a 60D can writes its own data through the sd-port to the card. primarily here's your upper limit.

regards chmee