Some CBCS-encrypted content has an all-zeros default_KID in the tenc box while the real KID is only in the PSSH boxes. mp4decrypt matches keys against the tenc KID, so it silently skips decryption when the provided KID doesn't match. This adds a track ID-based key fallback when a zero KID is detected, matching the existing shaka-packager zero-KID fallback behavior.
Replace removed `WrmHeader.read_attributes()` with `key_ids` property and add missing WRMHEADER v4.1-v4.3 XML paths (`DATA/PROTECTINFO/...`) to the base64 PSSH parser fallback.
Session keys from master playlists often contain PSSHs with multiple KIDs covering all tracks, causing licensing to return keys for wrong KIDs.
Changes:
- Unified DRM licensing logic for all downloaders
- Prefer media playlist EXT-X-KEY tags which contain track-specific KIDs
- Add filter_keys_for_cdm() to select keys matching configured CDM type
- Add get_track_kid_from_init() to extract KID from init segment with fallback to drm.kid from PSSH
- Track initial_drm_key to prevent double-licensing on first segment
- Simplify n_m3u8dl_re block to reuse common licensing flow
- Use strict PlayReady keyformat matching via PR_PSSH.SYSTEM_ID URN instead of loose substring match
- Fix PlayReady keyformat comparisons that incorrectly compared strings to PlayReadyCdm class
- Fix byterange header format in get_track_kid_from_init() to use HLS.calculate_byte_range()
Also fixes PlayReady keyformat matching in:
- unshackle/core/tracks/track.py
- unshackle/core/drm/playready.py
Fixes download failures where track_kid was null or mismatched, causing wrong content keys to be obtained during PlayReady/Widevine licensing.
Remove erroneous `.bytes` accessor from PSSH.SYSTEM_ID comparisons in from_track() and from_init_data() methods. The pyplayready PSSH.SYSTEM_ID is already the correct type for comparison with parsed PSSH box system_ID values.
* Introduced a new configuration option for DRM decryption in `unshackle.yaml`.
* Updated the `decrypt` methods in `PlayReady` and `Widevine` classes to allow using `mp4decrypt`.
* Enhanced the `Config` class to manage decryption methods per service.
* Added `mp4decrypt` binary detection in the binaries module.
