Audio capture records exactly SUNRISE_TARGET_SECS centred on sunrise

Previously sunrise-audio-capture.sh recorded the entire capture window
(70+ minutes) and daily_sunrise_video.sh sought to the right position with
a complex offset calculation.

Now: record floor(TARGET/2) seconds before sunrise and ceil(TARGET/2) after —
odd second goes to post-sunrise.  The file is exactly SUNRISE_TARGET_SECS long
and already centred, so no offset is needed when mixing.

AUDIO_PRE_BUFFER_MIN removed — it was part of the old whole-window scheme
and is no longer meaningful.

https://claude.ai/code/session_01C4jbd3waXG3eKZYbGUjLUQ

daily_sunrise_video.sh

@@ -171,10 +171,9 @@ audio_offset="0"
 cam_audio="$image_dir/sunrise-audio.m4a"
 if [ "${AUDIO_ENABLED:-false}" = "true" ]; then
     if [ -f "$cam_audio" ]; then
-        buffer_sec=$(( ${AUDIO_PRE_BUFFER_MIN:-2} * 60 ))
-        audio_offset=$(echo "scale=1; $SUNRISE_PRE_MIN * 60 + $buffer_sec - $SUNRISE_TARGET_SECS / 2" | bc)
+        # Already exactly SUNRISE_TARGET_SECS, centred on sunrise — no offset needed
         audio_src="$cam_audio"
-        echo "Audio: camera recording  offset=${audio_offset}s"
+        echo "Audio: camera recording (centred on sunrise)"
     else
         library_dir="$SCRIPT_DIR/sunrise-sounds"
         if [ -d "$library_dir" ]; then

sky-cam.conf

@@ -283,8 +283,9 @@ CAPTURE_INTERVAL=10
 # The audio file is deleted automatically after it is mixed into the video.
 #
 AUDIO_ENABLED=false           # set true if your camera has a working mic
-AUDIO_PRE_BUFFER_MIN=2        # extra minutes to start before the capture window
 CAPTURE_AUDIO_BITRATE=96k     # bitrate for the sunrise audio recording
+# Audio is recorded for exactly SUNRISE_TARGET_SECS, centred on actual sunrise:
+# floor(TARGET/2) seconds before, ceil(TARGET/2) after (odd second → post-sunrise).
 
 # ── Mattermost — daily sunrise upload ─────────────────────────────────────────
 # mattermost_url, access_token, channel_id go in .env (see bottom of this file).

sunrise-audio-capture.sh

@@ -1,13 +1,15 @@
 #!/bin/bash
-# sunrise-audio-capture.sh — record the camera's RTSP audio stream during the
-# sunrise window so daily_sunrise_video.sh can mix in natural ambient sound
-# (birds, rain, wind) at real speed while the video plays as a timelapse.
+# sunrise-audio-capture.sh — record exactly SUNRISE_TARGET_SECS of audio
+# centred on the actual sunrise moment, so daily_sunrise_video.sh can mix in
+# real ambient sound (birds, rain, wind) at natural speed.
 #
-# Triggered daily at 03:00 by sky-cam-audio-capture.timer.
-# Waits internally until (sunrise − SUNRISE_PRE_MIN − AUDIO_PRE_BUFFER_MIN),
-# then records for the full window.  Exits immediately if AUDIO_ENABLED≠true.
+# Triggered at 03:00 by sky-cam-audio-capture.timer; waits internally until
+# the right moment before recording.  Exits immediately if AUDIO_ENABLED≠true.
 #
-# Output: BASE_DIR/SUNRISE_CAM/YYYY-MM-DD/sunrise-audio.m4a
+# Recording window: floor(TARGET/2) seconds before sunrise,
+#                   ceil(TARGET/2)  seconds after  (odd second goes to post).
+#
+# Output: BASE_DIR/<cam>/YYYY-MM-DD/sunrise-audio.m4a
 # Deleted automatically by daily_sunrise_video.sh after mixing.
 
 set -euo pipefail
@@ -40,13 +42,16 @@ fi
 sunrise_time_local=$(TZ="$TIMEZONE" date -d "$sunrise_time" +"%H:%M:%S")
 echo "Sunrise (local): $sunrise_time_local"
 
-# ── Calculate wait and record duration ───────────────────────────────────────
+# ── Calculate recording window centred on sunrise ─────────────────────────────
 time_to_seconds() { IFS=':' read -r h m s <<< "$1"; echo $((10#$h*3600 + 10#$m*60 + 10#$s)); }
 
 sunrise_sec=$(time_to_seconds "$sunrise_time_local")
-buffer_sec=$(( ${AUDIO_PRE_BUFFER_MIN:-2} * 60 ))
-record_start_sec=$(( sunrise_sec - SUNRISE_PRE_MIN * 60 - buffer_sec ))
-record_dur_sec=$(( (SUNRISE_PRE_MIN + SUNRISE_POST_MIN) * 60 + buffer_sec ))
+half_pre=$(( SUNRISE_TARGET_SECS / 2 ))          # floor — pre-sunrise portion
+half_post=$(( SUNRISE_TARGET_SECS - half_pre ))  # ceil  — post-sunrise gets odd second
+record_start_sec=$(( sunrise_sec - half_pre ))
+record_dur_sec=$SUNRISE_TARGET_SECS
+
+echo "Audio window: ${half_pre}s before → ${half_post}s after sunrise (${record_dur_sec}s total)"
 
 midnight=$(date -d "today 00:00:00" +%s)
 now_day_sec=$(( $(date +%s) - midnight ))