audio-analysis

Audio Analysis

Pull the audio out of a video (or take a standalone audio file) and run an EBU R128 loudness pass. Output is a short markdown report with LUFS / dBTP / LRA and a recommendation against a chosen target.

This skill does not normalize. Apply normalization separately (with transcode or a future normalize-audio skill) once you've decided on a target.

Procedure

1. Inputs

Field	Default
Source	required (video or audio)
Mode	extract / analyze / both (default both)
Target	youtube (-14 LUFS / -1 dBTP) / broadcast (-23 / -2) / podcast (-16 / -1) / streaming-spotify (-14 / -1)
Output dir	sibling audio/ (or project's assets/ if inside an index project)

2. Extract

If the source is a video, pull the audio. Prefer stream-copy when the codec is sane (aac/opus/flac/mp3); otherwise re-encode to wav for analysis.

CODEC=$(ffprobe -v error -select_streams a:0 -show_entries stream=codec_name -of csv=p=0 "$SRC")
case "$CODEC" in
  aac|mp3|opus|flac) EXT="$CODEC"; ARGS="-vn -acodec copy" ;;
  *)                 EXT="wav";    ARGS="-vn -ac 2 -ar 48000 -c:a pcm_s24le" ;;
esac
mkdir -p "$OUT_DIR"
EXTRACTED="$OUT_DIR/$(basename "${SRC%.*}").$EXT"
ffmpeg -hide_banner -y -i "$SRC" $ARGS "$EXTRACTED"

3. Analyze (ebur128)

ffmpeg -hide_banner -nostats -i "$EXTRACTED" -af 'ebur128=peak=true:framelog=quiet' -f null - 2>&1 | tail -25

Parse the summary block at the end:

[Parsed_ebur128_0 @ ...] Summary:
  Integrated loudness:
    I:         -18.4 LUFS
    Threshold: -28.5 LUFS
  Loudness range:
    LRA:         8.1 LU
    Threshold: -38.5 LUFS
    LRA low:   -22.2 LUFS
    LRA high:  -14.1 LUFS
  True peak:
    Peak:       -1.3 dBFS

Pull I (integrated), LRA, and Peak with grep/awk.

Also probe stream metadata:

ffprobe -v error -select_streams a:0 -show_entries stream=codec_name,sample_rate,channels,bits_per_sample -of default=nw=1 "$SRC"

4. Compare to target

Target	Integrated	True Peak
YouTube	-14 LUFS	-1 dBTP
Spotify	-14 LUFS	-1 dBTP
Apple Music	-16 LUFS	-1 dBTP
Podcast	-16 LUFS	-1 dBTP
Broadcast (EBU R128)	-23 LUFS	-2 dBTP

Compute deltas (measured_I - target_I).

5. Write the report

<OUT_DIR>/<basename>.loudness.md:

# Loudness report — <basename>

- Source: `<absolute path>`
- Stream: aac, 48 kHz, 2 ch
- Target: YouTube (-14 LUFS / -1 dBTP)

| Metric | Measured | Target | Delta |
|--------|---------:|-------:|------:|
| Integrated | -18.4 LUFS | -14 LUFS | **-4.4 LU** (too quiet) |
| True peak | -1.3 dBTP | -1 dBTP | -0.3 dB (ok) |
| LRA | 8.1 LU | — | — |

**Recommendation:** raise integrated by ~4.4 LU. Use ffmpeg `loudnorm` (two-pass) or apply gain when re-encoding.

6. Print summary

Show the table inline so the user doesn't have to open the file. Offer:

• Run transcode with a loudnorm step.
• Try a different target (re-run analysis with a different reference — no re-extraction needed).