Transmuxing
Transmuxing is the process of moving audio and video streams from one container format into another without re-encoding them. For example, video arriving over RTMP can be transmuxed into HLS segments while the compressed picture stays exactly the same. Because nothing is decoded, transmuxing is fast, cheap and causes no loss in quality.
Why it matters
Transmuxing lets a service reach more devices without paying to re-encode video. It is how a live feed sent over RTMP or SRT becomes something a browser or phone can play. Because it avoids decoding, it adds very little delay or cost, which matters most for live events with large audiences.
How it works
- The system reads the incoming stream and separates the compressed video and audio data from the old container.
- It keeps the compressed data exactly as it is, with no decoding or re-encoding.
- It rewrites timing and track information into the new container, such as MPEG-TS or fragmented MP4.
- For streaming, it cuts the result into segments and writes a manifest so players can request them.
Is transmuxing lossless?
Yes, transmuxing is lossless because the compressed video and audio are copied without being changed. Only the container around them is rewritten. The picture and sound coming out are identical to what went in. This is why transmuxing is fast and cheap compared with transcoding, which decodes and re-compresses every frame.
Can I transmux RTMP to HLS?
Yes, RTMP to HLS is one of the most common transmuxing jobs, as long as the codecs inside are supported by HLS players. RTMP streams usually carry H.264 video and AAC audio, which HLS supports. The server repackages them into HLS segments and a playlist. If the encoder sends codecs or settings that players cannot handle, transcoding is needed instead. That repackaging server is one less thing to run on FastPix, which takes live feeds over RTMPS or SRT and delivers them to viewers as LL-HLS.
Where it's used
Live sports streamers and creator apps transmux live feeds into formats players understand, quickly and with no loss in picture quality.
By the numbers
- The HLS specification, RFC 8216, was published in August 2017 and allows media segments in MPEG-2 Transport Stream or fragmented MP4 formats. (RFC 8216: HTTP Live Streaming)
