Transcoding
/trænsˈkoʊdɪŋ/ · noun · verb · compression
Transcoding is converting media from one encoding to another, like HEIC to JPG or MOV to MP4.
In more detail
Transcoding decodes media from one format and encodes it again in another. Converting HEIC to JPG or WebP to PNG are both examples. Most file converters do this.
If the new format is lossy, transcoding loses some quality. Do it once, from the original file.
Transcoding vs remuxing
A full transcode decodes the media and encodes it again with a new codec. Remuxing moves the existing encoded streams into a different container without touching them. Remuxing is faster and loses no quality. It only works when the new container supports the original codecs.
Resizing, changing the frame rate, adjusting volume, burning in subtitles and applying filters all need decoded media. They usually mean a new encode. Changing the file extension does none of this and can't make an unsupported codec play.
How to transcode without losing quality
Start from the original or best quality source. Pick a codec that suits where the file is going. Skip extra in-between exports. If only the container is the problem, remux instead of transcoding.
For lossy output, check the hard parts: motion, texture, gradients, small text and dense music. A higher bitrate or quality setting can reduce new artifacts. It can't bring back detail missing from the source. Keep the original after you convert.
Key points
- Transcoding decodes and encodes again. Remuxing only changes the container.
- Filters, resizing and codec changes usually need a new encode.
- Start from the best source and avoid repeated lossy transcoding.