feat: support create subtitles (.srt)

README.md

@@ -1,10 +1,12 @@
 # Transcribe
 
-Requires Bash, FFmpeg, curl, jq, and standard coreutils.
+Requires Bash, FFmpeg, curl, jq, and standard coreutils; `--srt` also requires
+Python 3 and the accompanying `subtitles.py` file.
 
 ```sh
 ./transcribe recording.m4a
 ./transcribe video.mp4 > transcript.txt
+./transcribe --srt video.mp4 > subtitles.srt
 ```
 
 Accepts m4a, mp4, aac, flac, opus, mp3, ogg, wav, and other formats your
@@ -13,6 +15,14 @@ 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.
 
+`--srt` requests word timestamps using OpenRouter's `verbose_json` response.
+Words are grouped into cues of at most two lines (42 characters per line,
+except an unusually long unbroken word) and six seconds. Cues also break at
+sentence endings, pauses of at least 0.7 seconds, and speaker changes when
+speaker labels are available. Timing comes from the words, rounded to
+milliseconds. Subtitle output goes to stdout; missing or invalid word timestamps
+produce an error. Without `--srt`, output remains plain text.
+
 One file per invocation; the whole recording is sent in one request, so
 the service's audio length and request size limits apply.