S4C - which is directly subsidised by the government - will have to find extra funding to continue its current output of programmes.
The channel is spending more than it is receiving in income for a second year in a row, together with a steady fall in its audience share.
Chief executive Huw Jones said more had to be done to appeal to a wide audience, but added he was pleased at the 700,000 weekly viewing figures.
"I think what we need is a schedule that appeals equally to all parts of Wales, but it is difficult to get a perfect balance," he said.
Its hold on the Welsh-speaking audience in north Wales has dropped from 12.5% to 11% in the past year, following a fall in the previous 12 months.
Figures in south Wales show a more alarming 4% fall in viewing figures.
Average peak hours viewing share of S4C's Welsh-language programmes by Welsh speaking viewers was 13.8% compared to 15.3% in 2000.
The broadcaster is fighting back with more programmes tailored towards a younger audience, based round the growing popularity of Welsh medium education.
Commissioning editors at S4C are looking at specifically to try to gain a loyal audience.
But the company's immediate concerns lie with deciding on its digital provision in the coming year.
Some 700,000 people watch S4C's Welsh language output once a week, but the signs of decline will not be taking lightly by S4C's Authority or the Department of Culture in London which is its principal funder.
The channel has asked for a limited 2% above inflation funding increase to compete in the digital age.