Video Transcoding

Video Transcoding

With video, transcoding is the process of changing the resolution, quality, and/or encoding (parameters) of a video track, all of which involve re-encoding the entire video (and thus inevitable loss of quality).

With audio, transcoding is the process of changing the quality and/or encoding (parameters) of an audio track, both of which involve re-encoding the entire audio track (and thus inevitable loss of quality).

I am assuming here that we are working with lossy video and audio codecs, such as H.264 for video and AAC for audio.

1 Transcoding to a Lower Pixel Resolution

When transcoding to a lower pixel resolution, scale the video uniformly down so that it fits as best it can into the new smaller dimensions. Do not distort the video and do not create black or empty strips to either side (or top and bottom).

For example, screen video captured on a OnePlus 6 smartphone in portrait mode is 1080×2340 pixels. If this has to be transcoded to fit into FullHD portait at 1080×1920, then the new video size will be 886×1920, as shown in Figure 1.

Transcoding OnePlus 6 screen video down from 1080×2340 to 886×1920 pixel resolution.
Figure 1: Transcoding OnePlus 6 screen video in portrait mode down from 1080×2340 to 886×1920 pixel resolution.

Numerous web sites are available to help calculate the new proportions, for example:

2 Tools by Platform

The following subsections list some of the tools which are available for each platform.

Microsoft Windows

MacOS

Linux