M3U Playlists
An M3U playlist is a text file that lists media locations and can add descriptive information for each entry.
Open this M3U playlist and the reader sees an ordered set of media locations, with optional descriptions immediately before them:
#EXTM3U
#EXTINF:180,Opening song
Music/Opening.flac
#EXTINF:240,Second song
Music/Second.flac
#EXTM3U identifies the extended convention. Each #EXTINF line supplies a duration in seconds and a display title for the following location. The title is descriptive; the path is what the reader must open to obtain the sound.
Relative paths resolve from the playlist folder
If the playlist is stored in a folder called Concert, Music/Opening.flac conventionally refers to Concert/Music/Opening.flac. Moving only the playlist into another folder changes that relationship. An absolute location instead identifies its destination independently of the playlist's folder.
Opening the text succeeds before opening the media. A list can therefore display both song titles even if one referenced file is missing. That gives two distinct stages to test: parsing entries and obtaining each entry's content.
M3U8 commonly denotes UTF-8 text. That convention determines how text characters are represented; it does not turn every M3U8 into one particular kind of streaming presentation.
What HLS adds to the family
An ordinary music list describes an order of independent items. HLS gives playlists protocol-specific meanings: a media playlist lists timed segments of one presentation, while a multivariant/master playlist describes alternative streams. Tags govern durations, sequence updates, and other playback behaviour in addition to locations.
The reader must interpret the appropriate conventions, rather than merely follow every path as a new song. Emby's M3U tuner guidance concerns a channel list and its source descriptions, another distinct use of related text syntax.
When inspecting a playlist, first identify its job. Then read the actual location associated with the failing entry and the base location used to resolve it. The playlist organizes access; the referenced resource supplies the codec and container data.