add burning-audio-cd skill and scripts

4 files changed, 134 insertions, 0 deletions

diff --git a/prompts/skills/burning-audio-cd/SKILL.md b/prompts/skills/burning-audio-cd/SKILL.md
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+---
+name: burning-audio-cd
+description: Burns a Red Book audio CD-R from a directory of FLAC files on a Fedora Linux host. Converts each FLAC to 44.1 kHz / 16-bit / stereo WAV with ffmpeg, then writes them as CD-DA tracks with cdrskin in DAO mode. Use when the user asks to burn, write, or master an audio CD / CD-R / CD-RW from FLACs, or mentions a CD writer / DVD-RW USB drive with a music folder to put on it. Triggers on, burn audio CD, burn CD-R, master audio CD, write FLAC to CD, audio CD from FLAC.
+---
+
+# Burning audio CD-Rs from FLAC files
+
+End-to-end recipe for turning a folder of FLACs (already ordered and sized to
+fit on the disc, e.g. the output of `creating-cd-mixes`) into a real Red Book
+audio CD on Fedora Linux. The pipeline is: probe → install tools → transcode
+FLAC→WAV → burn with `cdrskin` → eject and clean up.
+
+## Tools
+
+- `cdrskin` (libburn family) — burner. Install with `sudo dnf install -y cdrskin`.
+- `ffmpeg` / `ffprobe` — transcoding and duration probing. Already present on
+  most Fedora installs (`ffmpeg-free` or `ffmpeg` from RPM Fusion).
+
+Do NOT try to `dnf install ffmpeg` blindly — Fedora has both `ffmpeg-free` and
+RPM-Fusion `ffmpeg`, and asking dnf to install the second one over the first
+fails with a conflict. Just verify `ffmpeg`/`ffprobe` are on PATH and skip
+installing if so.
+
+## Workflow
+
+1. **Identify the drive.** Run `lsblk` and look for an `sr*` device, or
+   `cdrskin --devices`. Confirm the disc is blank/erasable with:
+   ```bash
+   cdrskin dev=/dev/sr0 -minfo | tail -20
+   ```
+   Note the *Remaining writable size* in sectors (1 sec audio = 75 sectors;
+   80-min disc ≈ 359,844 sectors).
+
+2. **Verify the source fits.** Sum FLAC durations with `ffprobe` and confirm
+   the total ≤ disc length (74 or 80 min). If unsure, run
+   `scripts/probe_durations.sh /path/to/dir`.
+
+3. **Transcode FLAC → CD-audio WAV** into a tmp dir using
+   `scripts/flac_to_cdwav.sh /path/to/flacs /tmp/cd-burn`. Each WAV is
+   44.1 kHz / 16-bit / stereo little-endian PCM with a standard RIFF header
+   (cdrskin auto-detects and strips the 44-byte header).
+
+4. **Burn.** Run `scripts/burn_audio_cd.sh /tmp/cd-burn /dev/sr0 [speed]`
+   (default speed 16). It invokes:
+   ```bash
+   cdrskin dev=$DEV speed=$SPEED -v -force -dao -audio -pad <wavs sorted>
+   ```
+   - `-audio` switches to CD-DA mode (no ISO9660).
+   - `-pad` zero-pads the last sector of each track.
+   - `-dao` writes Disc-At-Once so there are no 2-second gaps between tracks.
+   - `-force` is required because cdrskin's *predicted session size* check is
+     overly conservative (adds ~50,000 sectors of headroom) and refuses
+     near-full 80-min discs even when the actual content fits. The real fit is
+     determined from the `Total size` / `Lout start` figures cdrskin prints
+     just before burning — those must be ≤ disc capacity.
+
+5. **Verify, eject, clean up.**
+   ```bash
+   eject /dev/sr0
+   rm -rf /tmp/cd-burn
+   ```
+
+## Gotchas
+
+- Audio-CD capacity is **time**, not bytes. Always reason in sectors/minutes,
+  never in MB.
+- Track order on the finished CD is the lexicographic order of the WAV
+  filenames at burn time. Keep the `NN - Title.flac` numbering when
+  transcoding.
+- Filenames with spaces / Unicode are fine for cdrskin but must be quoted in
+  shell loops. The scripts here use `find -print0` / `xargs -0` style safety.
+- The first attempted burn often fails with
+  `FATAL : predicted session size NNNNNs does not fit on media`. Re-run with
+  `-force` if the actual `Lout start` sector count is within the disc's
+  *Remaining writable size*.
+- Some drives (e.g. HL-DT-ST DVDRAM GUE0N) silently bump write speed up after
+  the first track or two; this is normal.
+
+## Scripts
+
+- `scripts/probe_durations.sh DIR` — prints each FLAC's duration and total.
+- `scripts/flac_to_cdwav.sh SRCDIR DSTDIR` — clears DSTDIR and transcodes
+  every `*.flac` in SRCDIR to a CD-audio WAV with the same basename.
+- `scripts/burn_audio_cd.sh WAVDIR DEV [SPEED]` — burns every `*.wav` in
+  WAVDIR to DEV as an audio CD (DAO, padded, forced).
diff --git a/prompts/skills/burning-audio-cd/scripts/burn_audio_cd.sh b/prompts/skills/burning-audio-cd/scripts/burn_audio_cd.sh
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+++ b/prompts/skills/burning-audio-cd/scripts/burn_audio_cd.sh
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+#!/usr/bin/env bash
+# Burn every *.wav in WAVDIR to DEV as a Red Book audio CD (DAO).
+# Tracks are written in lexicographic filename order.
+set -euo pipefail
+wavdir=${1:?usage: burn_audio_cd.sh WAVDIR DEV [SPEED]}
+dev=${2:?usage: burn_audio_cd.sh WAVDIR DEV [SPEED]}
+speed=${3:-16}
+
+mapfile -d '' -t wavs < <(find "$wavdir" -maxdepth 1 -type f -iname '*.wav' -print0 | sort -z)
+if [ "${#wavs[@]}" -eq 0 ]; then
+    echo "No WAV files in $wavdir" >&2
+    exit 1
+fi
+
+echo "Burning ${#wavs[@]} tracks to $dev at speed $speed..."
+cdrskin dev="$dev" speed="$speed" -v -force -dao -audio -pad "${wavs[@]}"
+echo "Burn complete."
diff --git a/prompts/skills/burning-audio-cd/scripts/flac_to_cdwav.sh b/prompts/skills/burning-audio-cd/scripts/flac_to_cdwav.sh
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+++ b/prompts/skills/burning-audio-cd/scripts/flac_to_cdwav.sh
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+#!/usr/bin/env bash
+# Transcode every *.flac in SRCDIR to a CD-audio WAV in DSTDIR
+# (44.1 kHz / 16-bit signed / stereo little-endian PCM).
+set -euo pipefail
+src=${1:?usage: flac_to_cdwav.sh SRCDIR DSTDIR}
+dst=${2:?usage: flac_to_cdwav.sh SRCDIR DSTDIR}
+mkdir -p "$dst"
+rm -f "$dst"/*.wav
+shopt -s nullglob
+count=0
+for f in "$src"/*.flac; do
+    base=$(basename "$f" .flac)
+    out="$dst/$base.wav"
+    ffmpeg -nostdin -loglevel error -y -i "$f" \
+           -ar 44100 -ac 2 -sample_fmt s16 -f wav "$out"
+    count=$((count+1))
+done
+echo "Wrote $count WAV files to $dst"
diff --git a/prompts/skills/burning-audio-cd/scripts/probe_durations.sh b/prompts/skills/burning-audio-cd/scripts/probe_durations.sh
new file mode 100755
index 0000000..0860fe3
--- /dev/null
+++ b/prompts/skills/burning-audio-cd/scripts/probe_durations.sh
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+#!/usr/bin/env bash
+# Print duration of every *.flac in DIR and the total in MM:SS.
+set -euo pipefail
+dir=${1:?usage: probe_durations.sh DIR}
+total=0
+shopt -s nullglob
+for f in "$dir"/*.flac; do
+    d=$(ffprobe -v error -show_entries format=duration -of default=nw=1:nk=1 "$f")
+    printf "%7.2f  %s\n" "$d" "$(basename "$f")"
+    total=$(awk -v a="$total" -v b="$d" 'BEGIN{printf "%.3f", a+b}')
+done
+mm=$(awk -v t="$total" 'BEGIN{printf "%d", t/60}')
+ss=$(awk -v t="$total" -v m="$mm" 'BEGIN{printf "%05.2f", t - m*60}')
+printf -- "----\nTOTAL: %s seconds (%d:%s)\n" "$total" "$mm" "$ss"