Shares in Blinkx plunged almost 8% early on Monday, after the internet media firm swung to an annual pre-tax loss.The London-listed company said heavy investments in a bid to address "rapid industry changes", a decline in revenue and pressure on margins contributed to a very difficult year.In the year to 31 March, the group posted a $24.8m (£15.8m) pre-tax loss compared with a $17.1m in the previous year, while revenue fell 13% year-on-year to $215m and operating costs rose edged 3.5% higher to $222.8m.The drop in revenue was attributable to "changing advertiser requirements" and a reduction in industry supply, Blinkx said in a statement on Monday.Meanwhile, the company said that a shift towards lower margin products and a rise in inventory costs will weigh on gross margin and profitability in the short-term future, although it aimed to restore its gross margins after a number of acquisitions."With the key portfolio acquisitions in place, we intend to redouble our focus on our integration efforts in financial year 2016, which will allow us to be even more responsive to customer demands and industry changes," said group chief executive Subhransu Mukherjee."We remain confident about our prospects in a dynamic industry."Blinkx shares were down 6.41% to 36.50p at 09:31 on Monday.