Video file formats / formats
What you want to know before making a video
Just as images have resolutions and file formats, there are some fixed formats and specifications for videos. Naturally, moving images, moving images, have more elements to define in the specifications, and the mechanism is complicated.
In fact, people in charge of marketing and promotion, advertising agencies, etc., can often feel disgusted by observing the presentation rules of each company.
This time, to dispel the weaknesses of those people, I would like to present a few main points that need to be understood in the video specs and the optimal video specs on major platforms like YouTube and Facebook.
1. Six Points Defining Video Specifications
Now, I would like to explain the six main points in the video specs.
1-1. Resolution
Like still images, videos have resolution. Image resolution refers to “size” and “pixel density”, but for moving images, resolution refers to “horizontal x vertical pixel count”.
The resolutions of familiar things are 720 x 480 SD image quality for DVD, 1920 x 1080 full HD for Blu-ray and 1440 x 1080 for digital terrestrial broadcast (* The reason why the aspect ratio is different from other will describe later).
Typical resolutions include
Full HD (1920 x 1080) / HD (1280 x 720) / SD (720 x 480) / 4K UHD (3840 x 2160)
.
Video resolution
Cameras like the iPhone X support 4K video recording and major streaming services like Netflix and Amazon Prime Video support 4K distribution.
Recently, with the expansion of smartphones and the rise of vertical signage, videos with long vertical resolutions and square videos like Instagram have also appeared.
Some people have said that “Full HD resolution is enough”, but the screen has gotten bigger, the price of 4K TVs has dropped, the drawing power of the smartphone screen has improved, and 4K / 8K has been improved. it has been generalized mainly by the Ministry of the Interior. Issues and Communications: As various efforts are made in this regard, it is expected that further progress will be made on a higher resolution.
1-2. Pixel aspect ratio
The pixel aspect ratio, also called the pixel ratio, represents the ratio of the width to the height of the pixels that make up the video data, and you can set the expansion / contraction ratio of the video during playback. Be careful as it is easy to confuse with the old resolution (aspect ratio of the video itself).
In digital terrestrial broadcasting, due to the compatibility with the conventional SD format and the amount of data, data with a resolution of 1440 x 1080 (4: 3) and a pixel aspect ratio of 4: 3 is distributed and stretched on the side of the TV. When doing so, the appearance is 16: 9, but it’s okay if you think you are basically using square pixels (1: 1) in WEB video.
1-3. File format (container), codec
To understand the file format of a video, you need to understand what is called a “codec.”
Audio and video data are stored in a “video file”.
In addition, data is compressed and encoded (also called encoding) using a “codec” so that it can be processed more efficiently and more easily by personal computer software.
In other words, when a video is played, it cannot be played unless the data is decompressed using the same “codec” as the “codec” used when compressing.
Note that the codec cannot be identified by the file extension alone. When making a request to a production company, be sure to also specify the codec.
To make it easier to understand, we will use “codec” as “key” and “video / audio data” as “treasure box”.
There are two treasure chests in the video archive, each locked with a different key. That is, to open the treasure chest and play the video, the key (= codec) corresponding to each treasure chest is required.
If you lock with “Key A” when generating video data and “Key B” when generating audio data, the video will play normally if you don’t have “Key A” and “Key B” in your hand. You can’t do it and if you only have “Key A”, you won’t be able to play the audio.
