Compression Techniques in Video Encoding

Video encoding entails altering the underlying formats and compressing the files, to boost parameters like performance, compatibility, or storage. It helps in a larger context like streaming content over internet, OTT, or IPTV mediums. With compression applied on video, it can be streamed to a larger volume of audience as the bandwidth utilized will be lower and issues of buffering can be avoided.

Typically the compression is achieved with the help of popular codec’s (encoder / Decoder) like H.264, VP9, and VP8. Their video encoder software uses different compression techniques in order to reduce the size of video content without bringing about a huge difference to the quality of the content being played.

Today, we look at some of the popular compression techniques used by video encoder software:

1 – Image resizing

By decreasing the resolution of a video, a lesser amount of information is presented in each frame. So a 1280×720 video (921,600 pixels per frame) will have more information than a 640×360 video (230,400 pixels per frame). Hence you can ‘shrink’ the image size via video encoder software by reducing the level of information and thus decrease the file size. Typically, videos ready for streaming will have different quality levels for the same content, and depending on the bandwidth, the appropriate quality can be selected for streaming.

By reducing the volume of pixels though, the amount of detailing in each frame goes down too. These results in what we call ‘pixilation’ of the video being displayed. So, such an image does bring down the amount of data consumed for transmission, it does affect the quality of the content being transmitted.

2 – Chroma sub sampling

The amount of detailing in colors needed will directly correlate to the space taken up by the video. The chroma subsampling method tries to reduce this detailing to bring down the space needed. Since the human eye can detect a difference in luminance better than chroma detailing, the method tries to keep luminance intact and reduces chroma information. The interplay of the individual RGB elements determines the compression of the image.

3 – Interframes and video frames

This is an emerging video compression technique used by video encoder software. It checks the images in the frames displayed per second and removes redundant information to bring down the detailing displayed per second.

If a video has 30 frames per second (fps) frequency rate then this technique will assess whether the frames remain the same within that one second. If yes, then this method will remove the redundant data for frames where an element is not altered across frames. So, if there is a large area that remains unchanged across frames (for e.g. the visual of a sky in a scene) then that element is reused in the next frame to save space.

There are 3 types of frames used in this technique:

1 – i-frame – This is the full frame image of the video and will be encoded with varied keyframe interval. The more frequency of i-frame creation, the more will be the space needed.

2 – p-frame – The predictive frame consists of partial elements within an image. It assesses the previous i-frame or another p-frame to see if any area of the image is redundant and can be excluded.

3 – b-frame – The bi-directional predictive frame too contains partial elements but unlike the p-frame’s ability to assess only previous frames, the b-frame can look both ahead and at previous frame to offer better compression with optimum viewing experience.

4 – Changing the frame rate

The number of frames per second (fps) is directly correlated to the space taken up by the video. By decreasing the frame rate, the video will need lesser amount of data to be streamed through. While it does show instant impact, appropriate care has to be taken when choosing this method of compression with video encoder software.

If you reduce the frame rate too much, there are chances that the content will bring about a jarring effect instead of the fluid movement that happens between scenes in the video.

To conclude

These compression techniques ensure that there is an optimum balance of the video quality and its eventual size when streaming to individual users.

Let us know which is the technique primarily used in your OTT/IPTV business. We would love to hear from you.

Compression Techniques in Video Encoding
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