Skip to main content
OT

OBS and streaming tech: audio routing, subtitles and encoding

How to route audio in OBS, wire up a virtual audio cable, overlay bilingual subtitles with chroma key, and pick encoder settings for overseas viewers.

The technical difference between a normal stream and a cross-border stream is not the video. It is the number of audio paths.

A normal stream has one: the host speaks, the audience hears it. A cross-border stream has at least three:

  1. Original voice — what the host actually says;
  2. Translated voice — synthesised speech in the target language;
  3. Monitoring — what the host hears in their own headphones.

These three go to different places, and OBS’s default audio model is “mix every input into one output”. Nearly every cross-border audio failure traces back to never having separated them.

What this topic covers

Audio routing is the backbone. A virtual audio cable (VB-Cable on Windows, BlackHole on macOS) is essentially a software patch bay: it connects one application’s output to another application’s input without going through physical speakers and microphones. Once that model clicks, the rest follows.

Subtitle overlays come second. OBS has no native live captioning, so the standard approach is to have the translation tool render captions in a window with a solid background colour, capture that window in OBS, and key the colour out — OBS categorises Color Key as the filter for graphics and windows, and Chroma Key as the one for green screens and camera footage. Any program that can draw text becomes a subtitle source, at the cost of dealing with window capture scaling, DPI and capture methods.

Encoder settings come last. Your audience is on the other side of the world, so the delivery path is longer than a domestic stream and the bitrate and keyframe trade-offs differ.

Suggested reading order

If you are building this for the first time, work through it in this order so that each step is independently verifiable:

  1. Get the virtual audio cable working: confirm the translated voice reaches OBS and that the host can monitor it;
  2. Add chroma key subtitles: confirm captions keep pace with speech;
  3. Tune the encoder last: confirm overseas viewers are not buffering.

Do not tune all three at once. Failures in audio, subtitles and encoding impersonate each other — subtitle lag looks like slow translation when it is actually an oversized stream buffer.

Articles in this topic