Duplicate Data Resulting from Custom Tags

[slipthebit]

CustomTags are parsed in twice when using DecodeWith. This happens because both decodeLineOfMasterPlaylist and decodeLineOfMediaPlaylist are called in decode, and both parse the CustomTags seperatley.

This issue can be observed using the Master Manifest, https://devstreaming-cdn.apple.com/videos/streaming/examples/img_bipbop_adv_example_fmp4/master.m3u8, and CustomTag example in Issue #160 detailed by @slugalisk.

The Master Manifest includes 5 #EXT-X-MEDIA tags, but DecodeWith produces 10 Values for the CustomTag.

The go-playground link below duplicates the issue as of 9/20/2023 with v0.12.0
https://goplay.tools/snippet/e_p-kLnpqco

[slipthebit]

As a workaround to the issue, I filter out duplicates in the Custom Tag Decode function.

Using the example from Issue #160, I modified the Decode function to be:

func (tag *ExtXMediaTag) Decode(line string) (m3u8.CustomTag, error) {
	val := &ExtXMediaTagValue{}
	
         for k, v := range m3u8.DecodeAttributeList(line) {
		switch k {
		case "TYPE":
			val.Type = v
		case "GROUP-ID":
			val.GroupID = v
		case "CHANNELS":
			val.Channels = v
		case "NAME":
			val.Name = v
		case "LANGUAGE":
			val.Language = v
		case "DEFAULT":
			val.Default = v == "YES"
		case "AUTOSELECT":
			val.AutoSelect = v == "YES"
		case "FORCED":
			val.Forced = v == "YES"
		case "URI":
			val.URI = v
		}
	}
	
         //prevent duplication - ref: https://github.com/grafov/m3u8/issues/201
	dup := false
	for _, t := range tag.Values {
		if *t == *val {
			dup = true
			break
		}
	}

	if !dup { 
		tag.Values = append(tag.Values, val)
	}

	return tag, nil
}

[slipthebit]

Alternatively, if the playlist type is known, the CustomTags can be added to the playlist itself before decoding.
https://goplay.tools/snippet/COz0f_dEbA9