Parse keyid from multi-key widevine PSSH

[yajin2021]

This PR will...

Parse keyId for widevine. PSSH box defines as follows:

aligned(8) class ProtectionSystemSpecificHeaderBox extends FullBox('pssh', version, flags=0)
{
    unsigned int(8)[16]                SystemID;
    if (version > 0)
    {
         unsigned int(32)              KID_count;
         {
             unsigned int(8)[16]       KID;
         } [KID_count];
    }
    unsigned int(32)                   DataSize;
    unsigned int(8)[DataSize]          Data;
}

The length of the DataSize and Data fields is not always 6. For widevine, it is defined in WidevineCencHeader.proto

Why is this Pull Request needed?

Parse KeyId for widevine correctly

Checklist

• changes have been done against master branch, and PR does not conflict
• new unit / functional tests have been added (whenever applicable)
• API or design changes are documented in API.md

[robwalch]

1. Remove unnecessary conditionals (no need to check keyBytes and results[0] or psshData? multiple times)
2. keyId still needs to be set if kids were not parsed

Suggested change

	if (!this.keyId && keyBytes) {
	const results = parseMultiPssh(keyBytes.buffer);
	if (results[0] && 'version' in results[0]) {
	const psshData = results[0];
	if (psshData?.kids?.[0]) {
	this.keyId = psshData.kids[0];
	}
	}
	}
	if (!this.keyId) {
	const results = parseMultiPssh(keyBytes.buffer);
	const psshData = results[0];
	if (psshData && 'version' in psshData && psshData.kids?.[0]) {
	this.keyId = psshData.kids[0];
	} else {
	const offset = keyBytes.length - 22;
	this.keyId = keyBytes.subarray(offset, offset + 16);
	}
	}

• I considered making a similar change (use parseMultiPssh) in Fix Widevine KEYID parsing #7380, but I couldn't find examples of version 1 pssh with kids containing a key. In every example, the KEYID was in the playlist, so that clients don't need a protobuf parser. Most content available to me has version 0 wv pssh.

Do you have content where this fix is necessary?

Fixing the key id parsing from the pssh would require at least some protobuf parsing. That isn't something we should do when standard practice is to include the KEYID attribute. We can still take this fix, if you need it.

[yajin2021]

Because I still use v1.5.x, I added this modification. Parsing the value from KEYID tag in playlist first for v1.6.7, the problem will not occur. But the logic of parsing keyId from URI is still inaccurate. If the version of PSSH is 0, KEYID does not exist. The keyid obtained by offsetting 6 bytes is incorrect.
Because the license request requires a dynamic token, I cannot create a test stream with PSSH version 1 now. But I have a simple example for playlist. The version of PSSH is 1 and the length of DataSize and Data is 5.

#EXTM3U
#EXT-X-VERSION:6
#EXT-X-PLAYLIST-TYPE:VOD
#EXT-X-TARGETDURATION:6
#EXT-X-MEDIA-SEQUENCE:292092204
#EXT-X-INDEPENDENT-SEGMENTS
#EXT-X-MAP:URI="ibOQs5Rcy/init_video_1100.m4s"
#EXT-X-PROGRAM-DATE-TIME:2025-07-15T04:20:26.012Z
#EXT-X-KEY:METHOD=SAMPLE-AES,URI="skd://AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA1",KEYFORMAT="com.apple.streamingkeydelivery",KEYFORMATVERSIONS="1"
#EXT-X-KEY:METHOD=SAMPLE-AES-CTR,URI="data:text/plain;base64,AAAASHBzc2gBAAAA7e+LqXnWSs6jyCfc1R0h7QAAAAGqqqqqqqqqqqqqqqqqqqqhAAAAFAgBEhCqqqqqqqqqqqqqqqqqqqqh",KEYID=0xAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA1,KEYFORMAT="urn:uuid:edef8ba9-79d6-4ace-a3c8-27dcd51d21ed",KEYFORMATVERSIONS="1"
#EXT-X-KEY:METHOD=SAMPLE-AES-CTR,KEYFORMAT="com.microsoft.playready",KEYFORMATVERSIONS="1",URI="data:text/plain;charset=UTF-16;base64,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"
#EXTINF:6.000000,
ibOQs5Rcy/media_video_1100-292092204.m4s
#EXTINF:6.000000,
ibOQs5Rcy/media_video_1100-292092205.m4s
#EXTINF:6.000000,
ibOQs5Rcy/media_video_1100-292092206.m4s
#EXTINF:6.000000,
ibOQs5Rcy/media_video_1100-292092207.m4s
#EXTINF:6.000000,
ibOQs5Rcy/media_video_1100-292092208.m4s
#EXTINF:6.000000,
ibOQs5Rcy/media_video_1100-292092209.m4s
#EXTINF:6.000000,
ibOQs5Rcy/media_video_1100-292092210.m4s
#EXTINF:6.000000,
ibOQs5Rcy/media_video_1100-292092211.m4s
#EXTINF:6.000000,
ibOQs5Rcy/media_video_1100-292092212.m4s
#EXTINF:6.000000,
ibOQs5Rcy/media_video_1100-292092213.m4s
#EXTINF:6.000000,
ibOQs5Rcy/media_video_1100-292092214.m4s
#EXTINF:6.000000,
ibOQs5Rcy/media_video_1100-292092215.m4s
#EXTINF:2.000000,
ibOQs5Rcy/media_video_1100-292092216.m4s
#EXT-X-ENDLIST