If you are using Adobe Premiere Pro and export to H.264, at the bottom there is Bitrate Settings. In other editing software (and also in software converter) usually there is setting of this.
This setting is almost never touched. Usually we just let it go.
But, does it matter if we change the value?
Yes, it affects:
Video file size
It is the most secure is we do not have to touch it, alias let aja fit his preset. But, in certain cases we can play it. For example, we can decrease file size to be sent via email for client preview.
In this article we will discuss what is bitrate, what is its effect, what is CBR, 1-pass VBR, and 2-pass VBR.
What is bitrate?
All media based on digital data in principle is just a collection of bits (the smallest unit of all data in the computer). Collection of bits is what makes us able to see images, sound, text, video … on PC, internet, smartphone, or other digital media.
The bits themselves have only two values: 1 or 0. But from 1 and 0 this, the computer can arrange them into anything .. and display them on the screen.
Simple example .. when a photo is displayed, the computer basically just reconstruct the bits (which have been created by a digital camera or scanner) to the screen.
Indeed we see it as if instant (without pause). It was as though the picture was already there. But actually, the PC takes time to reconstruct it. It’s just so fast, our eyes can not see the process.
(Is not it when you open a web page with lots of pictures when your internet is slow it takes time?)
Now imagine … the video is a collection of images (frames) that alternate every fraction of a second (remember frame rate). Automatically, a set of bits will continue to be processed as long as the video is playing.
So simple bitrate is:
The number of bits that are processed every second by a video file when the video is played.
Usually the units are kilobits per second (Kbps) or megabits per second (Mbps).
The table below is an example bitrate recommended by Youtube.
To see bitrate, you can play it in player (VLC, MPC, QuickTime Player, etc) and see its properties.
The effect of bitrate on quality and file size
We take the example of 720p format.
In the table above, you can see that the 720p format (1280 x 720 pixels), Youtube recommends bitrate 5 Mbps.
What if the value we set lower than that and higher than that?
The figure below is a comparison of 3 export results I made to a 720p (25 fps) DSLR file with 3 different bitrates: 1 Mbps, 5 Mbps, and 10 Mbps.
Can you see that the 1 Mbps bitrate for 720p is very poor quality. While 5 Mbps and 10 Mbps almost no visible difference.
Then we can conclude that 5 Mbps is sufficient value to export 720p with good quality.
Then note the size of the third file (the duration I use is only 10 seconds).
The higher the bitrate, the bigger the file.
Need to set bitrate manually?
The example I did above is manually setting the bitrate in Premiere, by sliding the slider in the bitrate settings.
Is this manual bitrate setting necessary?
Depending on the situation. But, most do not need.
Premiere itself (and software editing in general) already provides presets for various purposes: Youtube, Vimeo, Android, iPhone, etc. whose bitrate values have been adjusted.
Try to see if you change the preset .. You will see the value of bitrate is different.
This is because the ability of each tool (device) is different in playing the video. Some are able to operate it in high bitrates, some are not.
On that basis the presets are made.
So .. to be safe, you should keep using presets.
(I mostly use the “Youtube 720p HD” preset for general editing of DSLRs, since this preset is the safest to play on any device .. Even if not for upload to Youtube)
But If you want to set it manually, remember the consequences:
Changing the bitrate will not improve the video quality that was originally bad
Raising the bitrate will enlarge the file
Raising the bitrate should pay attention to the playback device, capable or not
Lowering the bitrate can reduce the file, but the quality will drop
I used to change the bitrate just to decrease the size of the edited file to be sent to the client, before the final I send. Because it will save the quota, and .. withstand the high resolution (until the pay is liquid:>).
Constant bitrate bitrate is variable
There are two types of bitrate settings:
CBR (Constant bitrate)
VBR (Variable bitrate)
What is the difference?
The word “constant” on CBR means that as long as the video is playing, its bitrate is always constant. It does not matter whether the current image is completely black or displays a complex image (like crowded people), the bitrate does not change.
While the “variable” in VBR means that as long as the video is playing, its bitrate will vary depending on the picture condition. In the simple image, the bitrate will be low, but in the complex image, the bitrate will be high.
Then the settings of an bitrate on CBR and VBR will be different. In VBR you have to specify the target bitrate and maximum bitrate, since the value will vary between the two values when the video is played.
Which one is better: CBR or VBR?
For a typical situation, VBR is better. Because the video will adjust the bitrate to the condition of the picture. The quality can be maintained as long as the video and file will be relatively smaller than the CBR. Because it does not need to waste a bit when the image is simple (eg black screen when fade in fade out).
Whereas if you use CBR .. the images are too complex the quality will drop than the simple image, because he must maintain the bitrate.
So you can say: in CBR, bitrate is kind of budget. You have to do with a ‘budget bit’ so much.
CBR is required in special situations where the most important airing is delivered.
Broadcast a television show for example. Television impressions prioritize the smooth transmission. Therefore the bitrate is made constant, because it does not want to risk the rising bitrate that causes the impression is disturbed because the transmitter is not strong to receive the signal.
So on broadcast cameras, usually the video formats in the form of CBR.
VBR 1-Pass and VBR 2-Pass
There are two types of VBR: 1-Pass and 2-Pass.
The main difference lies in the encoding process. Simply put, 1-pass is only one way, while 2-pass is twice the way.
That is 2 times the way .. first, Premiere will analyze the entire frame to decide how the value of a suitable bitrate for each frame. Secondly, it was only he did the encoding (export).
Then export with 2-pass, the time will be longer than 1-pass.
Whether 2-pass more produces better quality than 1-pass is still debatable.
Some call 2-pass better .. because it has been analyzed first. So each image will be given the right bitrate value without having to waste the whole bit.
Knowing bitrate is important, because it is related to video quality.
Although ultimately it is safer to use presets .. At least, you know why a preset uses a certain bitrate.
Especially for streaming, adjusting bitrate with internet speed is crucial to avoid buffering.
You can open this link to see Youtube recommendations as a guide for the video files you will upload.
May be useful!