Slow starts and buffering

There are two different complaints here, with different causes.

A film takes a long time to start

This is almost always the file plus how fast your provider serves it.

Before a film can show its first picture, the player has to read enough of the file to know how to play it, and with many provider films that takes a while. How long depends almost entirely on your provider and your connection to it. On a weak link a large film can take many seconds to start. That is the file and the speed of the provider, not something wrong with the app.

What helps with a slow film start

A better connection to the provider. This is the one thing that really changes it, and the app already does what it can at its end without being asked.
A smaller file. Where a provider offers the same title more than once, the lighter version starts sooner. Try Variants on the title.
Fetch films over several connections, on Android phones, tablets, Android TV and Fire TV, in Settings → Player. It helps where a provider caps the speed of a single connection. Turn it off again if films then pause and start over every few minutes, and leave it off if your account allows only one connection.

Buffer size does not fix a slow start

No buffer setting will change it. The buffer decides how much is held once data arrives, not how fast it arrives. If somebody tells you to raise the buffer to fix a slow start, they are wrong.

Telling a slow start from slow seeking

Look at the total time on the seek bar. While it still says 0:00, the film has not really started yet. That is a start, not a seek.

It plays, then stops to buffer

Buffering means the picture is waiting for the next part of the stream. Two questions decide what helps, so answer them first:

Is it a live channel or a film? They buffer for different reasons.
Is it one channel, or everything? One channel points at that channel or its version; everything points at the connection, the Wi-Fi or the account.

Everything buffers, every channel and every film

The Wi-Fi. A box at the far end of the house, behind walls, or a busy 2.4 GHz network is the most common cause. Try it with a cable or next to the router: if it is smooth there, it is the Wi-Fi, and no setting in the app changes that.
The provider’s evening rush. When a provider is overloaded, every app on every device buffers at the same hours. Check another app on the same network at the same time.
Two devices on one stream. On an account that allows one stream at a time, two devices take it from each other and each stops when the other starts. The app says so: Your provider allows one stream at a time and they are all in use. Stop the other device, see HTTP 403 and 509.

A live channel stops for a moment, again and again

Raise Buffer size, in Settings → Player: Large, or Very large if the pauses are longer. Some providers send the picture in bursts with gaps between them; a larger buffer holds more before the picture starts, so the gaps no longer reach the screen. The price is that each channel starts a little later, so changing channels feels slower. Go back to Auto if it does not help. Buffer size is on Android phones, tablets, Android TV and Fire TV, and on Apple TV once VLC is picked as an engine.
When it happens as the connection dips, set Live stream format to HLS in the playlist’s details. HLS can step down to a lower quality instead of stopping. See Live channels.
Try another version of the channel with Versions in the player: it often comes from another server of the provider.
A channel in HLS played by VLC ignores Buffer size and Low latency live, because it keeps its own buffer. If you want those settings to work on it, set the format back to MPEG-TS or play live channels on the other engine.
Low latency live together with Large or Very large gives away part of what each one does. If the channel stops, turn Low latency live off first.

A live channel freezes and stays frozen

The app notices that the stream stopped arriving and opens the channel again by itself; the player shows Reconnecting while it does. If the picture is not back within about half a minute, press Restart channel in the player. If it keeps happening on the same channel, set Live stream format to HLS for that playlist. A larger Buffer size does not change this one.

A film stops in the middle to buffer

Raise Buffer size to Large or Very large. It holds more of the film ahead of you, so a connection that stalls now and then stops interrupting you. It does nothing for a connection that is simply too slow for the film: then a lighter version under Variants helps.
A film that stops every few minutes, shows its start again for a moment and plays on: turn Fetch films over several connections off, in Settings → Player.
On weak Wi-Fi or a small box: set Buffer size to Small and keep Fetch films over several connections off.

Multiview windows stop

Buffer size and Low latency live do not apply to the windows of multiview: each window keeps a small buffer of its own. If the windows stop, use fewer of them, or set the formats and engines above for the channels in them.

When a buffer change seems to do nothing

A new Buffer size, Low latency live or engine applies when the channel or film starts again; if something is playing, it starts again with the new setting. Live stream format is set per playlist, on each device, so with two playlists change it in both, and on the television as well as the phone.

It buffers here but plays in another app

Two players can treat the same stream differently, so this is worth working through in order:

Switch the engine for what you are watching: Player settings → Player engine on a phone, Options → Player engine on a television, or the green button on an Android TV or Fire TV remote. If it plays smoothly on the other one, make that the default in Settings → Player: Engine for live channels for channels, Player engine for films. Windows, the Mac and LG and Samsung TVs have one engine.
Try another version of the channel with Versions in the player.
Close the other app while you compare. On an account that allows one stream, two apps take it from each other, and each stops to buffer when the other one starts.
For a live channel that stalls whenever the connection dips, set Live stream format to HLS in the playlist’s details, see Live channels.
For a film, try a larger Buffer size, as above.

If one channel still buffers only here, report it with the channel, the time, your device and the version, and say which other app plays it.

Seeking is slow in a film

Every jump asks the provider to start serving the film from a new place, so a slow provider is slow again at each jump.

In a catch-up stream, seeking is different by nature: a jump lands near where you dropped the marker rather than exactly on it, and plays on from there.

The app itself is slow, not the video

Different problem. A very large playlist makes the first open of a screen slow while the catalogue is indexed. It settles. If it does not, trimming categories is the lever with the biggest effect.

The logo at start

The IPTV Deck logo you see when the app opens is not an intro, so there is nothing to skip or turn off. It stays on screen while the app opens your playlists and your settings, and Home takes its place as soon as it is ready. On an older box it stays longer.

If the logo never goes away, close the app fully, see An update that changed nothing for how on each device, open it again and report it if it happens again.