M3U

The format is about as simple as a format gets. Each entry is two lines: one starting with #EXTINF that names the thing, and one with the address it lives at. Everything else — logos, channel numbers, the groups that become categories in a player — arrived later as attributes people agreed to put on the #EXTINF line. No standards body ever ratified any of it.

That informality is why M3U files vary so much. One provider writes group-title="Sports", another writes group-title="SPOR", a third leaves it out entirely and expects the player to guess. A player that handles IPTV well is mostly a player that has met a lot of badly written M3U files.

The confusion with M3U8 is worth clearing up: the 8 refers to UTF-8 text encoding, nothing more. Every HLS playlist is an M3U8, but not every M3U8 is HLS — an IPTV channel list saved as UTF-8 is also an .m3u8 and has nothing to do with segmented streaming.

Provider lists have grown in a way the format never anticipated. A file that was a few hundred lines in 2010 is now, from a large provider, hundreds of thousands of entries and hundreds of megabytes of text.

The naive way to read one — load the file into memory, parse it, hold the result — falls over long before that. Parsing a 200 MB list that way means a memory spike an iPhone will not tolerate, and iOS ends the app rather than waiting. This is why so many IPTV apps simply crash on a large provider.

The approach that works is to never hold the list at all: read it from disk in pieces, write each channel straight into a database as it is parsed, and then page the screen from that database. FoxDL was measured against a 485 MB list of two million channels — 123 seconds to import, 9 MB of extra memory, 4 milliseconds to draw the first page, 400 milliseconds to search the whole list. The numbers are only interesting because the naive approach cannot produce them at all.