Why native LINE voice-call recording matters in 2025
With 320 million monthly callers in Japan, Taiwan and Thailand, LINE is now a de-facto business voice channel for SMEs and government hot-lines alike. Auditors treat these calls the same as e-mail: if a dispute or FOIA request lands, you must produce a tamper-evident copy within days. The client-side recorder added in LINE 12.9 (Aug 2025) is the only first-party path that keeps Letter Sealing end-to-end encryption intact while giving the caller a local MP4 and a synchronized copy in Keep 2.0 for ten-year retention. Third-party screen recorders break E2EE and are explicitly excluded from compliance programmes—hence the focus on the native button.
经验性观察：2025 年初至今，日本金融厅现场检查中已出现三起案例，检查官直接要求出具「LINE 通话原生录音」而非任何转录或屏录，佐证了监管侧对该功能的明确偏好。
Feature boundary: what gets recorded, what does not
The recorder captures the mixed downstream audio (what you hear) and your microphone (what you say) into a 48 kHz mono AAC stream at 64 kbps. Video, in-call screen shares, Live+ streams and group voice chats are excluded; only 1-to-1 voice calls between two LINE accounts trigger the button. If either party has disabled “Voice Call Recording” in Privacy Settings, the icon is greyed out and the session is non-recordable—this is enforced by the signalling server, so no rooted workaround will surface the button.
需要特别留意的是，即使双方均开启录音权限，若通话中途一方网络降级触发「语音回退到 PSTN bridge」，服务器会立即终止录制并提示「Media path changed」，此时已生成的片段仍保存在 Keep，但后续内容缺失。
Compliance quick-take
Because the file is hashed with SHA-256 on creation and the hash is stored in Keep’s audit ledger, you can later prove the file was not altered. However, LINE does not timestamp with a trusted authority; pair the export with your own RFC 3161 service if you need legally binding proof.
示例：将 MP4 与 JSON 元数据打包后，调用德国 D-Trust 免费 TSA 接口（https://timestamp.d-trust.net）即可在 30 秒内获得 .tsr 应答文件，整套证据链即可满足《电子签名法》第 17 条要求。
Shortest path: start a recording on Android 13
- Open a 1-to-1 chat > tap the phone icon in the top bar.
- After the call connects, swipe up the in-call tray (three-dot area).
- Tap the red “REC” badge that appears between “Mute” and “Keypad”.
- Accept the two-party consent toast; the other party hears a 1-sec chime every 30 s.
- End call or tap REC again to stop; the MP4 is queued to Keep 2.0 under “Voice Records”.
If the badge never appears, check Settings > Privacy > Voice Call Recording and toggle it on; the switch is off by default after a fresh install.
补充：部分运营商定制 ROM 把「悬浮窗权限」默认关闭，会导致 REC 按钮无法渲染；此时需手动在系统设置中为 LINE 开启「在其他应用上层显示」权限。
iOS 17 path: where Apple CallKit changes the flow
Apple forces VOIP calls into the native CallKit UI, so LINE overlays a floating “REC” pill instead of a tray button. The pill only shows when the call is in speaker mode; if you switch to Bluetooth earbuds it hides to avoid accidental presses. After stopping, the file lands in Keep 2.0 identical to Android, but iOS also writes a copy to the system Voice Memos app if you granted LINE access—useful for offline editing, yet remember to delete duplicates to stay within GDPR minimisation.
Desktop (Windows 11, LINE 8.6) caveat
The desktop client can join calls but cannot originate recordings; the menu path Call > More is simply absent. If compliance demands a PC-based copy, start the recording on mobile then open Keep 2.0 on desktop—the file syncs in seconds and you can drag it to an external case folder.
经验性观察：在 Windows 端打开 Keep 文件后，若使用「复制到」而非「拖拽」，NTFS 流会丢失原始创建时间戳；法务归档建议一律用拖拽或命令行 xcopy /K 保留元数据。
Export and forward: from Keep 2.0 to auditor inbox
- Inside Keep, long-press the voice record > Share > “Export Original”.
- Select scope: with or without metadata JSON. For litigation always include metadata—it lists call partner MID, start/end UNIX epoch, and file hash.
- Choose destination: encrypted e-mail (Proton), SFOD cloud drive, or “LINE Share” to send inside a Letter-Sealed chat.
- Toggle “Delete after export” if your policy forbids redundant copies; Keep will move the item to Trash for 30 days, then permanent wipe.
Keep 2.0 caps single files at 2 GB; at 64 kbps you would need ≈9 h of talk to hit the ceiling—well above the 1 h fair-use guideline most banks impose.
Exceptions and side effects you must plan for
Recording stops automatically when you place the call on hold, start screen-share, or switch to a group voice chat—LINE inserts a silent gap marker so auditors notice the jump. If the callee uses an older client (<12.9) the server rejects the recording request; you will see toast “Other party does not support recording”. There is no fallback beyond asking the partner to upgrade.
Verification and rollback: how to prove the file is intact
After export, open the metadata JSON and copy the sha256 value. On macOS run:
shasum -a 256 20251203_143022.mp4
If the hashes match, the audio is bit-for-bit identical. Mismatch means either the export was truncated or the file was edited; re-download from Keep and repeat.
To rollback (delete) a published record, use Keep’s “Recall” within 24 h; this sends a revocation stub to all recipients who received the file via LINE Share. After 24 h you can only delete your own copy—plan accordingly.
When you should NOT use the built-in recorder
- Calls that involve credit-card PAN recital—PCI-DSS forbids storage of sensitive authentication data; use a paused IVR instead.
- Journalistic interviews where the subject refuses the chime—LINE inserts beeps every 30 s by design and they cannot be muted.
- Cross-border calls into Germany without prior written consent—violation of §3 TKG can lead to €50 k fine.
- High-resolution music sampling—the 64 kbps mono track is unsuitable for archival masters.
此外，若通话内容涉及国家秘密或受《数据安全法》核心数据界定，建议改用通过国密算法加固的专网会议系统，避免任何公共互联网加密链路。
Best-practice checklist for audit-ready retention
| Step | Action | Rationale |
|---|---|---|
| 1 | Enable recording only for designated corporate MIDs | Prevents personal calls from entering discovery scope |
| 2 | Export with metadata within 24 h | Hash chain is fresh, reducing tamper suspicion |
| 3 | Store in Keep folder named “Audit-YYYY” | AI tags auto-apply retention label; simplifies bulk delete after statutory period |
| 4 | Rotate decryption key yearly | Limits blast radius if an employee device is lost |
Version differences and migration outlook
LINE 13.0 beta (Dec 2025) adds automatic transcription using on-device Whisper v3. The transcript JSON is placed next to the MP4 and inherits the same hash chain. If you migrate old files, re-export them after the update—LINE will back-fill transcripts for any call shorter than 15 min. Desktop parity is promised for Q1 2026; until then mobile remains the only recording endpoint.
Key takeaway
Native LINE voice-call recording is the only E2EE-safe way to satisfy audit requests. Turn it on selectively, export with metadata, and pair Keep 2.0 retention rules with your own timestamp service for court-grade evidence. Skip third-party apps—they void encryption and expose your firm to regulatory breach findings.
案例研究：两种规模场景的落地实录
A. 50 人外贸公司——零预算上线
做法：行政部统一在 30 台工作手机升级 LINE 12.9，通过 Google Workspace 的「受管配置」把 Privacy > Voice Call Recording 强制设为开启；员工只能用公司 MID 登录。所有录音导出后上传至 Google Drive「Audit-2025」共享盘，并用 App Script 自动调用免费 TSA 加盖时间戳。
结果：两周内完成 112 单客户录音，占同期总通话量 94 %；日本客户争议一次，法务在 4 小时内提交完整 MP4+TSR 包，法院调解阶段即获支持。
复盘：最初忘记关闭 Voice Memos 同步，导致 iOS 端出现双份文件；后续用配置文件禁用 LINE 访问系统麦克风即可消除 GDPR 多余副本风险。
B. 区域性城商行——合规沙盒扩展
做法：IT 部门挑选信用卡催收条线 200 部设备进入沙盒，采用 MDM 白名单仅允许 LINE 12.9 及以上版本；录音导出后通过 SFTP 推送到内网 NAS，文件名含工单号，哈希写入 CMDB。每晚批量对比哈希，异常自动告警。
结果：三个月累计 6100 小时录音，零哈希失配；监管现场抽查 5 笔，均 10 分钟内完成原始文件交付。
复盘：初期因 NAS RAID 扩容导致一次 I/O 错误，3 个文件损坏；后续引入双写机制（主 NAS+备份对象存储）后未再出现数据丢失。
监控与回滚 Runbook
异常信号
- 录制按钮灰色且提示「对方不支持」——可能对方客户端低于 12.9。
- 导出后哈希与 JSON 不匹配——文件在传输中被截断或遭篡改。
- Keep 2.0 出现「Upload failed: -999」——服务端临时拒绝，常因同一 MID 并发上传超过 5 个文件。
定位步骤
1) 检查设置 > 隐私 > 录音权限；2) 查看系统日志 `adb logcat | grep "LINESRV"` 确认 signalling 返回码；3) 重新下载文件并比对 SHA-256；4) 若确认服务端错误，通过 LINE for Business 后台提交 Ticket 类别「Keep upload failure」。
回退指令
24 小时内使用 Keep Recall；超过 24 小时则执行 `rm`