Transcoding
TechnicalThe process of decoding a media stream and re-encoding it into a different format or bitrate.
What is Transcoding?
Transcoding is the direct digital-to-digital conversion of one encoding to another. In video calling, this typically involves taking a compressed video stream from a participant, decoding it into raw video frames, and then re-encoding it using different settings.
Types of Transcoding
- Transrating: Changing the bitrate (e.g., converting a high-bandwidth 2Mbps stream to a 500kbps stream for mobile users).
- Transsizing: Changing the resolution (e.g., downscaling 1080p to 360p).
- Transcoding (Format): Changing the codec (e.g., converting VP8 video to H.264 so it can be played on Safari or legacy devices).
When is it Used?
Transcoding is computationally expensive and introduces latency. It is primarily used in MCU (Multipoint Control Unit) architectures where the server mixes streams, or for recording and broadcasting (RTMP) where a standard format is required. In contrast, SFU (Selective Forwarding Unit) architectures avoid transcoding to keep latency low, preferring techniques like Simulcast.