HandBrake · Primary-source explanation; examples are illustrative. Instructions are based on publisher guidance; a UK IPTV account was not tested on this platform.
Choose a question for the preview
HandBrake documents a live preview workflow which encodes a selected short portion using the chosen settings. This is useful before committing substantial time to a long permitted source. First decide what needs checking: movement, dark detail, fine lettering or a particular subtitle. A quiet opening title is a weak sample for judging a later fast moving sequence. The preview should exercise the question which might change your encoding decision.
Keep the comparison small and traceable
For an original example, suppose a family recording includes a slow introduction, a busy outdoor scene and small lettering near its end. Preview the outdoor scene to assess movement and another portion to inspect the lettering. Keep source, range and playback display stable while comparing one relevant setting. Name or note the settings associated with each result so the preferred preview can be reproduced. A higher numbered label alone is not a visual comparison.
Check what the sample cannot establish
Wait until the encoded preview is ready before judging the result, and replay it if needed. A successful short sample does not establish that every later scene, audio track or subtitle will be correct. Before discarding any original, inspect the completed full output at several positions and confirm the selected tracks. This workflow saves time by finding an obvious problem earlier; it provides no measured encoding speed, guaranteed quality threshold or universal preset recommendation.