Media diagnostics · Primary-source explanation; no UK IPTV implementation or account test. Instructions are based on publisher guidance; a UK IPTV account was not tested on this platform.
Treat track selection as a separate decision
An output file can look correct while containing only part of the input’s track inventory. Encoder settings describe how selected material is handled; they do not necessarily say which material was selected. Before changing quality presets, compare the number and identities of audio and subtitle streams in the original and output. Work on a duplicate and retain a record of the command that produced it.
Examine a hypothetical two-language input
Imagine an input with a stereo English track and a six-channel French track. If an automatic selection rule favours the track with more channels, the outcome can be technically consistent with that rule while failing the viewer’s language requirement. More channels is not the same thing as the preferred language. Similarly, retaining one audible track does not prove the original commentary or audio-description option survived.
Use the tool’s documented mapping model
FFmpeg documents automatic stream selection and an explicit -map mechanism. Its current documentation explains that the automatic rules choose one stream of each acceptable type, with audio channel count among the criteria; explicit mappings allow deliberate selection. Review those rules for your installed version and intended output. A codec-copy setting alone should not be interpreted as an instruction to retain every track or attachment in the input.
Verify the user-facing choice
After preparing a permitted output, inspect its track inventory and open the player’s audio selector. Confirm that the intended option exists and plays the expected language or commentary. Do this before deleting intermediate work. If the output format cannot represent a required stream, reconsider the packaging or use an appropriate authorised conversion path rather than silently accepting a file that has lost an accessibility or language option.