diff --git a/README.md b/README.md
index 84f6d04..94d4691 100644
--- a/README.md
+++ b/README.md
@@ -9,7 +9,8 @@ export OPENROUTER_API_KEY='sk-or-v1-...'
 ```
 
 Accepts m4a, mp4, aac, flac, opus, mp3, ogg, wav, and other formats your
-FFmpeg supports. Uses the first audio track, converts it to mono 16 kHz WAV,
+FFmpeg supports. Uses the first audio track, converts it to mono 16 kHz MP3
+at 64 kbps (requires FFmpeg's libmp3lame encoder),
 and sends it to OpenRouter's `microsoft/mai-transcribe-2` model. Temporary
 files are removed on exit. The transcript goes to stdout; errors to stderr.
 
diff --git a/transcribe b/transcribe
index 4f0d68d..41933a3 100755
--- a/transcribe
+++ b/transcribe
@@ -29,12 +29,12 @@ trap 'exit 143' TERM
 
 # Normalize any FFmpeg-readable audio (or the first audio track in a video).
 ffmpeg -nostdin -hide_banner -loglevel error -i "$(realpath -- "$1")" \
-    -map 0:a:0 -ac 1 -ar 16000 -c:a pcm_s16le "$tmp/audio.wav"
+    -map 0:a:0 -ac 1 -ar 16000 -c:a libmp3lame -b:a 64k "$tmp/audio.mp3"
 
 # Keep large audio payloads out of shell arguments (which have a size limit).
-base64 <"$tmp/audio.wav" | tr -d '\n\r' >"$tmp/audio.b64"
+base64 <"$tmp/audio.mp3" | tr -d '\n\r' >"$tmp/audio.b64"
 jq -n --rawfile data "$tmp/audio.b64" \
-    '{model: "microsoft/mai-transcribe-2", input_audio: {data: $data, format: "wav"}}' \
+    '{model: "microsoft/mai-transcribe-2", input_audio: {data: $data, format: "mp3"}}' \
     >"$tmp/request.json"
 
 curl --silent --show-error --fail-with-body \