What Is Bit Rate? « Videomaker Community Forums

lmenningen
Member

I've been aware of bitrate as a tech parameter relating to video quality but I don't understand it.

Where is there an explanation of how bit rate affects video quality (not just an assertion that it does, but an explanation of How it does!)

Thanks - Lee

Posted 4 months ago #
Rob Grauert
Post Production Host

It's quite simple, really. The bit rate is the amount of data dedicated to a second of video. So, the higher the bit rate, the better the video quality. The higher the bit rate, the more bandwidth is needed to play back the video. And the higher the bit rate, the more data storage is required per second of video.

Rob Grauert, Jr
http://www.robgrauert.com
http://command-r.tumblr.com

Posted 4 months ago #
lmenningen
Member

One usually thinks of a 1920x1080 frame as High Definition whereas a 800x600 or whatever would be of lower quality. So HD is considered better than SD. But what is different in a 1920x1080 frame at 5 Mbps and a 1920x1080 frame at 23 Mbps and a 1920x1080 frame at 50 Mbps?

Each has 2,073,600 pixels and each pixel is described by so many bits of RGB, etc. And you're talking so many frames per second. Those are constants. So when you vary the bit rate, such as in Adobe Premiere, what exactly is it that you are varying???

Posted 4 months ago #
Kenkyusha
Member

The number/quality of samples. Compare it to audio- the higher the sample rate, the more audio information contained, so for bit rate, you are talking about chroma and other information.

Posted 4 months ago #
lmenningen
Member

Sorry I'm so dense, but as soon as you talk about "sample" and "audio" I visualize an analog signal being converted to digital. Regarding bit rate, we are talking about an existing digital file wherein "sampling" doesn't apply very well.

I visualize a video file with its header, followed by "pixel" fields. For an uncompressed file, the first field is for pixel 1,1 and has a hex XXX for Red, a hex XXX for Blue, a hex XXX for Green, and a hex XXX for alpha. Next comes a field for pixel 1,2, with it's data, then pixel 1,3 with it's data, etc. up through pixel 1920,1080 or whatever its final resolution. Compression apparently "scrubs" this data to eliminate redundant data according to the codec algorithm, right? So the amount of data for each pixel is fixed, but the inclusion or absence of a pixel would be determined by the codec. But within a specific codec such as h.264, what is "bit rate" when the amount of data is a constant??????

Isn't there a write-up somewhere that would explain bit rate and these pixel fields?

Posted 4 months ago #
EarlC
Moderator

Here's what Wikipedia says ... BIT RATE

Posted 4 months ago #
Jackson Wong
Administrator

Also, here is the first article I found concerning bit rate, hopefully this gives you another place to start,

http://www.videomaker.com/article/12713/

Posted 4 months ago #
tunguy
Member

Thanks for pointing us to that article Jackson.This is first time that I have began to understand Bit rate ("I'm non the wiser, but I'm much better informed")!

Posted 4 months ago #