Differences

This shows you the differences between two versions of the page.

--- linux:rip-audio-cd [2026/01/26 12:14] – Wuff
+++ linux:rip-audio-cd [2026/02/01 13:14] (current) – [Trim silence from start/end] Wuff
@@ Line 34: / Line 34: @@
 ====== Trim silence from start/end ======
+This reencodes the file
 <code>
 ffmpeg -i input.mp3 -af silenceremove=1:0:-50dB:stop_periods=1:stop_duration=0:stop_threshold=-50dB output.mp3
+</code>
+This copies the frames without quality loss:
+<code bash trim_mp3_silence_copy.sh>
+#!/usr/bin/env bash
+set -euo pipefail
+# trim_mp3_silence_copy.sh
+#
+# Usage:
+#   ./trim_mp3_silence_copy.sh input.mp3 [output.mp3]
+#
+# Env vars you can override:
+#   NOISE_DB   (default: -40dB)  threshold for silencedetect
+#   MIN_DUR    (default: 0.5)    minimum silence duration to consider (seconds)
+in="${1:-}"
+out="${2:-}"
+if [[ -z "${in}" ]]; then
+  echo "Usage: $0 input.mp3 [output.mp3]" >&2
+  exit 1
+fi
+if [[ ! -f "${in}" ]]; then
+  echo "Input file not found: ${in}" >&2
+  exit 1
+fi
+if [[ -z "${out}" ]]; then
+  base="${in%.*}"
+  out="${base}.trimmed.mp3"
+fi
+NOISE_DB="${NOISE_DB:--40dB}"
+MIN_DUR="${MIN_DUR:-0.5}"
+# Get full duration (seconds, as float)
+duration="$(ffprobe -v error -show_entries format=duration -of default=nw=1:nk=1 "$in")"
+# Run silencedetect and capture lines
+sd="$(
+  ffmpeg -hide_banner -nostats -i "$in" \
+    -af "silencedetect=noise=${NOISE_DB}:d=${MIN_DUR}" \
+    -f null - 2>&1 | grep -E 'silence_(start|end):' || true
+)"
+if [[ -z "$sd" ]]; then
+  echo "No silence detected (noise=${NOISE_DB}, d=${MIN_DUR}). Copying original -> ${out}" >&2
+  cp -f -- "$in" "$out"
+  exit 0
+fi
+# First silence_end => start of audio
+start_keep="$(awk '/silence_end:/ {print $NF; exit}' <<<"$sd")"
+# Last silence_start => end of audio (trailing silence start)
+end_keep="$(awk '/silence_start:/ {v=$NF} END{if(v!="") print v}' <<<"$sd")"
+# Fallbacks / sanity
+if [[ -z "${start_keep:-}" ]]; then
+  # No leading silence_end found; keep from 0
+  start_keep="0"
+fi
+if [[ -z "${end_keep:-}" ]]; then
+  # No trailing silence_start found; keep to full duration
+  end_keep="$duration"
+fi
+# Ensure start < end (handle edge cases)
+ok="$(
+  awk -v s="$start_keep" -v e="$end_keep" 'BEGIN{ if (s+0 < e+0) print "1"; else print "0"; }'
+)"
+if [[ "$ok" != "1" ]]; then
+  echo "Could not determine a valid trim window." >&2
+  echo "Detected start_keep=${start_keep}, end_keep=${end_keep}, duration=${duration}" >&2
+  echo "Silencedetect output:" >&2
+  echo "$sd" >&2
+  exit 2
+fi
+echo "Input:  $in"
+echo "Output: $out"
+echo "Keep:   ${start_keep}s -> ${end_keep}s (duration ~ $(awk -v s="$start_keep" -v e="$end_keep" 'BEGIN{printf "%.3f", (e-s)}'))"
+echo "Detect: noise=${NOISE_DB}, min_silence=${MIN_DUR}s"
+# Stream-copy trim (no re-encode). Use -ss/-to after -i for more accurate seeking while still copying.
+ffmpeg -hide_banner -y -i "$in" -ss "$start_keep" -to "$end_keep" -c copy "$out"
+</code>
+Then use as
+<code>
+chmod +x trim_mp3_silence_copy.sh
+./trim_mp3_silence_copy.sh input.mp3
+# or
+NOISE_DB=-35dB MIN_DUR=0.3 ./trim_mp3_silence_copy.sh input.mp3 out.mp3
 </code>