I've just tried the "livestreamer" method. It runs much faster than "ffmpeg", but there are still a couple of errors :
Code:
[cli][info] Found matching plugin stream for URL hlsvariant://stmw1.rthk.hk/aod/_definst_/radio/archive/radio4/Liveon4/mp3/mp3:20150321.mp3/playlist.m3u8
[cli][info] Available streams: 70k (worst, best)
[cli][info] Opening stream: 70k (hls)
[download][01.ts] Written 15.5 MB (2m4s @ 52.0 KB/s)
[stream.hls][error] Failed to open segment 188: Unable to open URL: http://stmw1.rthk.hk/aod/_definst_/radio/archive/radio4/Liveon4/mp3/mp3:20150321.mp3/media_w739913464_188.ts (timed out)
[download][01.ts] Written 43.4 MB (5m27s @ 73.1 KB/s)
[stream.hls][error] Failed to open segment 523: Unable to open URL: http://stmw3.rthk.hk/aod/_definst_/radio/archive/radio4/Liveon4/mp3/mp3:20150321.mp3/media_w1960685163_523.ts (timed out)
[download][01.ts] Written 59.6 MB (7m29s @ 516.6 KB/s)
[cli][info] Stream ended
The errors are fatal, because the resultant "01.ts" cannot be played.
I think nullacht's conclusion is right, that my network connection is not stable enough for lengthy downloading. I'll try at different times when the traffic is less busy.
Thanks again for recommending the useful tools.