I am also seeing the same issue, running MC 26.0.30 (selecting "Play trailer" reports "There is nothing to play"). Are others seeing this issue?
I have attached the log file. The following failure is reported in the log file while trying to play the trailer.
0008672: 6376: Import: JRAnalyzer::AddFile: Start
0008672: 6376: Import: JRAnalyzer::AddFile: Filename: webmedia://YouTube/5U2AJvU3bl4
0008672: 6376: Reader: CWinINetReader::Open: Start
0008672: 6376: Reader: CWinINetReader::Open: Opening webmedia://YouTube/5U2AJvU3bl4
0008672: 8564: Reader: CWinINetReader::Thread: Start
0008672: 8564: Reader: CWinINetReader::Thread: url: webmedia://YouTube/5U2AJvU3bl4
0008672: 8564: Reader: CWinINetReader::Connect: Start
0008672: 8564: Reader: CWinINetReader::Connect: Finish (0 ms)
0008672: 8564: Reader: CWinINetReader::Thread: failed, unknown protocol.
0008672: 8564: Reader: CWinINetReader::Thread: Finish (0 ms)
0008672: 6376: Reader: CWinINetReader::Open: ConnectToURL failed, m_bConnectError=true, URL=webmedia://YouTube/5U2AJvU3bl4