If you extend what you already have,
$line =~ m/StreamTitle='(.*?)(?:'|\z)/i;
or just
$line =~ m/StreamTitle='(.*?)'?/i;

However, if you replace the .*? with the more predictable [^']*, you don't even have to match the end quote:
$line =~ m/StreamTitle='([^']*)/i;

Update: I knew I avoided .*? for a reason. Struck out a bad "solution".