Write pssh boxes to generated moov box

[tbranyen]

Write the pssh boxes to the generated moov box when writing out during
segmentation initialization. This is required otherwise Chrome will not
trigger an onEncrypted event.

[tbranyen]

While this triggers the onEncrypted event, it does not seem to produce the correct ArrayBuffer value that is required to set the mediaKeys. I'll keep iterating on this branch.

[tbranyen]

I compared the init pssh data with and without mp4box:

• Without: 678
• With: 618

Looks like a loss of 60 bytes.

---

More notes:

• When reading the boxes layout using the mp4box file reader I counted the byte lengths, and when added together reached the correct 678 bytes
• Looking at the parsed boxes in the moov box, I see 20 bytes missing from each pssh box, but yet in the visualizer they look to have the correct lengths

---

Found the missing 20 bytes, looks like the default write will obviously miss pssh-specific metadata, in this case it's the system id which gets saved as hex, but written back as a uint8 array. This accounts for the offset.

[tbranyen]

Trying to follow this format, but hitting some roadblocks. Will attempt to get pssh writing done by EOD.

var pssh = [
    0x00, 0x00, 0x00, 0x44, 0x70, 0x73, 0x73, 0x68, // BMFF box header (68 bytes, 'pssh')
    0x01, 0x00, 0x00, 0x00,                         // Full box header (version = 1, flags = 0)
    0x10, 0x77, 0xef, 0xec, 0xc0, 0xb2, 0x4d, 0x02, // SystemID
    0xac, 0xe3, 0x3c, 0x1e, 0x52, 0xe2, 0xfb, 0x4b,
    0x00, 0x00, 0x00, 0x02,                         // KID_count (2)
    0x30, 0x31, 0x32, 0x33, 0x34, 0x35, 0x36, 0x37, // First KID ("0123456789012345")
    0x38, 0x39, 0x30, 0x31, 0x32, 0x33, 0x34, 0x35,
    0x41, 0x42, 0x43, 0x44, 0x45, 0x46, 0x47, 0x48, // Second KID ("ABCDEFGHIJKLMNOP")
    0x49, 0x4a, 0x4b, 0x4c, 0x4d, 0x4e, 0x4f, 0x50,
    0x00, 0x00, 0x00, 0x00,                         // Size of Data (0)
];

[tbranyen]

Got it working! I had to compare the data using a hex editor since the spec defined a different format. My guess is that this code will need to be reworked a little and can defer to @cconcolato to help with that. This gets me unblocked for now at least.