feat(ID3): decode APIC frames

[pszemus]

Since the official ID3 site (https://id3.org) is not available, I used a mirror (https://mutagen-specs.readthedocs.io/en/latest/id3/id3v2.4.0-frames.html#apic) to implement the decoding of APIC frames.

[shaka-bot]

Incremental code coverage: 88.00%

[avelad]

@pszemus can you provide a sample stream to test the code? Thanks!

[pszemus]

Here's a sample live HLS stream: https://stream-cdn-1.open.fm/OFM18/ngrp:standard/playlist.m3u8 with ID3 frames inserted at each song change: TIT2, TLEN, WOAF and APIC

In this stream, each APIC frame contains the following informationf:

• MIME Type: --> indicating that Picture Data will store an image URL
• Picture Type: 3 indicating that this is the Cover (front) picture according to https://mutagen-specs.readthedocs.io/en/latest/id3/id3v2.4.0-frames.html#apic
• empty Description
• Picture Data: a string with an image URL

Above should map to the following metadata object being thrown:

{
    "key": "APIC",
    "description": "",
    "data": "https://open-fm.wpcdn.pl/cover/c4a07f00000100000000000000005df37761082777840000",
    "pictureType": 3,
    "mimeType": "-->"
}

and it does, according to unit tests I wrote.

What bothers me is why Shaka Player replaces the pictureType field name set in id3_utils.js with ph in the metadata object (in my build), leaving mimeType, description and data field names unchanged. The metadata is logged as follows:

player.addEventListener('metadata', (e) => {
   console.log("[t: " + player.getMediaElement().currentTime + "] MetadataEvent event", e.payload);
});

and the result of the parsed APIC frame:

{
    "key": "APIC",
    "description": "",
    "data": "https://open-fm.wpcdn.pl/cover/c4a07f00000100000000000000005df37761082777840000",
    "ph": 3,
    "mimeType": "-->"
}

[avelad]

@pszemus I fixed the problem. Thanks for your PR!