Video Size Difference Stuff (can't think of any other titles)

[Guest]

I have a question in my mind and haven't found anyone discussing bout it in the internet. maybe I'm just dumb

Anyhow, here's the question:

 

Consider Two videos: Same Length, Resolution

 

Video1: Just black. Nothing else No audio, no nothing. blackness for 10 mins straight

 

Video2: Video bout a random guy's new blanket for 10 mins [No audio]

 

As the resolution and the length of the video are the same and no audio for both, will file size of both videos be the same?

 

[minibois]

Assuming everything is equal, it depends on if the bitrate is set to CBR or VBR.

Bitrate is the amount of data per second the video contains, higher bitrate is a larger file, but also better quality. A lower bitrate of course is the opposite.

 

CBR is Constant Bitrate, meaning it's always a certain number. If both files are rendered at CBR, they will be exactly equal in size.

VBR stands for variable bitrate and as its name implies, it doesn't keep the bitrate at a constant amount. The video rendering program will probably see that between one from and another there is no changes on Video2, so why render it again, wasting valuable bitrate? 

 

See your video as a painting on a canvas, that continuously gets redrawn every frame.

You can look at the canvas, see the current frame and new frame and redraw the entire new frame. OR you just redraw all the new parts. MP4 kind of does the redraw the new parts thing.

Bitrate would be the amount of paint you use though, so if you have a low bitrate, you are using a little amount of paint, so the quality will be worse. That is what CBR does.

With VBR it checks how much should be redrawn and chooses how much paint (bitrate) to use accordingly.

 

Good introduction video on compression, if you are interested:

 

TL;DR: if it is set to constant bitrate (CBR), both videos are exactly the same size. At variable bitrate (VBR) not.

[mariushm]

If it's different content, then file size will be different. Unless both video and audio is compressed with stupid settings like "constant / fixed bitrate with padding" or both video and audio is uncompressed.

 

Modern video and audio compression packs each second in an amount of bytes, which isn't fixed. A second with lots of motion or explosions or camera panning/zooming will require more bytes to compress compared to a more static sequence, so if the videos are somewhat different, the final size will inevitably be different.

 

With your specific example:

 

The blank video will compress in very little space... the video codec will compress each frame (image) in the video as an instruction that says something like "there's a 1280x720 area starting from coordinates 0,0 on screen : fill area with black color"  .... so your 1280x720 x 3 bytes per pixel movie gets compressed in around 100-300 bytes  (in reality, codecs split the frame in 64x64 pixel squares and then those squares are further split in as low as 4x4 blocks and information about these squares is recorded... so a black frame will have multiple "here's a 64x64 pixel square, fill it with black" ).

The next frame in the video would be "copy previous frame here", so basically a few bytes of information.

 

The random guy on blanket video will use more space, because the video codec will have to analyze every tiny motion of that person and write for each picture "person's head moved 3 pixels to the left and will move 5 more pixels over the next 5 frames" ... stuff like that... in each frame there's gonna be some minor changes that must be recorded.

 

 

 

[LaFemmeEnVert]

5 hours ago, ProBubble01 said:

I have a question in my mind and haven't found anyone discussing bout it in the internet. maybe I'm just dumb

Anyhow, here's the question:

 

Consider Two videos: Same Length, Resolution

 

Video1: Just black. Nothing else No audio, no nothing. blackness for 10 mins straight

 

Video2: Video bout a random guy's new blanket for 10 mins [No audio]

 

As the resolution and the length of the video are the same and no audio for both, will file size of both videos be the same?

 

For videos of the same resolution, same length. same bit rate, same codec, without audio, but one has no image or even a the same single frame throughout the entire length (like a still image instead of moving) and the other has moving elements, the one with moving eleements will be larger than one with no actual image or single frame throughout.

[Thanatopsis]

the files will be different using any modern format as they all use Key frames in some way shape or form.  that being said there are some older formats that don't use key frames but they were rare.