Greatly appreciated posts medtnaculus!
You've posted a wealth of interesting music on your youtube channel, I hope they stay up, just beware of using recordings from companies who are very anti-copyright vigilant such as Hyperion etc. I've seen too many awesome score videos be taken down for this reason.
It's not just record companies - that would be the case only with recordings issued commercially by such companies - but in any case there's more than one copyright to be considered here; in fact, there are usually four - those of the record company (where there is one), the publisher (where there is one), the performer and the composer. In the case of record companies and publishers, it is always possible to request their permission (provided that they're still in existence), in that of the performer/s it's also sometimes possible and in the case of the composer it's safest to adhere to the 70 year rule, under which, of the composers posted above, Bridge and Blumenfeld are in the public domain.
This can often be a problem because of the conflict of interest between the need to preserve legitimate copyright and the desire to share worthwhile performances of worthwhile music, epsecially that which is under-represented and otherwise unavailable or hard to source.
Record companies invest their money in making recordings, so anything that might risk compromising their subsequent income from them is likely to persuade them to be vigilant; much the same goes for publishers, especially in cases where their scores are included with uploaded recordings. With the performers, it's rather more limited to a matter of courtesy, as most would not likely sustain noticeable financial loss just because someone's uploaded their performances. As to the composer, whilst many who are alive would likely welcome the exposure provided by such uploads, most cannot afford for their royalties to be compromised and many composers depend heavily upon those as a vital income source - not all composers can live on commissions alone!
The best way to try to address and overcome these issues is to ask permission first wherever possible.
Best,
Alistair