There are only a couple of actual live performances by F&S on youtube (shortage of actual video of them); I imagine that the large number of other videos probably divide fairly evenly between people putting graphics to the audio recordings and amateur covers (of the usual range of quality).
If you don't know, I should probably mention that Michael Flanders suffered from Polio - you can see in the real video clips that breathing requires unusual (and very obvious) physical effort for him. Some people find this disturbing and/or upsetting, especially if they're not expecting it. (His voice control is very good despite having effectively no intercostal muscles and being chairbound. Listening to the audio without video, the only clue that there's anything wrong is that he takes very frequent breaths while singing; impressive for a man who has to move his shoulders up and down to breathe at all....)
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If you don't know, I should probably mention that Michael Flanders suffered from Polio - you can see in the real video clips that breathing requires unusual (and very obvious) physical effort for him. Some people find this disturbing and/or upsetting, especially if they're not expecting it. (His voice control is very good despite having effectively no intercostal muscles and being chairbound. Listening to the audio without video, the only clue that there's anything wrong is that he takes very frequent breaths while singing; impressive for a man who has to move his shoulders up and down to breathe at all....)