Sales and Marketing. Sales and marketing expenses consist primarily of personnel and related expenses for our sales and marketing staff, including salaries, benefits, incentive compensation, commissions, stock-based compensation and travel costs, amortization of acquired intangible assets, in addition to costs associated with marketing and promotional events, corporate communications, advertising, other brand building and product marketing expenses and allocated overhead. Our sales and marketing expenses have increased in absolute dollars in each of the last three years. We intend to continue to invest in sales and marketing and expand the sale of our product offerings within our existing customer base, build brand awareness and sponsor additional marketing events. Accordingly, we expect sales and marketing expense to continue to be our most significant operating expense in future periods. Over the long term, we believe that sales and marketing expense as a percentage of revenue will decrease, but will vary depending upon the mix of revenue from new and existingcustomers and from small, medium-sized and enterprise customers, as well as changes in the productivity of our sales and marketing programs.
General and Administrative. General and administrative expenses consist primarily of personnel and related expenses for executive, legal, finance, information technology and human resources functions, including salaries, benefits, incentive compensation and stock-based compensation. General and administrative expenses also include the costs associated with professional fees, insurance premiums, other corporate expenses and allocated overhead. Over the long term, we believe that general and administrative expenses as a percentage of revenue will decrease.
Merger-related. Merger-related costs consisted of expenses incurred during the three and six months ended June 30, 2019 of $2.6 million and $5.6 million, respectively, as part of the acquisition of the online video platform assets of Ooyala Inc. and certain of its subsidiaries, or Ooyala and costs related to the transition of Ooyala customers to the Company’s technology.
Other Income (Expense), net
Other expense consists primarily of interest income earned on our cash, cash equivalents, and foreign exchange gains and losses.
Income Taxes
As part of the process of preparing our consolidated financial statements, we are required to estimate our taxes in each of the jurisdictions in which we operate. We account for income taxes in accordance with the asset and liability method. Under this method, deferred tax assets and liabilities are recognized based on temporary differences between the financial reporting and income tax bases of assets and liabilities using statutory rates. In addition, this method requires a valuation allowance against net deferred tax assets if, based upon the available evidence, it is more likely than not that some or all of the deferred tax assets will not be realized. We have provided a valuation allowance against our existing U.S. net deferred tax assets at December 31, 2018. We maintain net deferred tax liabilities for temporary differences related to our foreign subsidiaries.
Stock-Based Compensation Expense
Our cost of revenue, research and development, sales and marketing, and general and administrative expenses include stock-based compensation expense. Stock-based compensation expense represents the fair value of outstanding stock options and restricted stock awards, which is recognized as expense over the respective stock option and restricted stock award service periods. For the three months ended June 30, 2019 and 2018, we recorded $1.4 million and $1.8 million, respectively, of stock-based compensation expense. For the six months ended June 30, 2019 and 2018, we recorded $2.8 million and $3.5 million, respectively, of stock-based compensation expense. We expect stock-based compensation expense to increase in absolute dollars in future periods.
Foreign Currency Translation
With regard to our international operations, we frequently enter into transactions in currencies other than the U.S. dollar. As a result, our revenue, expenses and cash flows are subject to fluctuations due to changes in foreign currency exchange rates, particularly changes in the euro, British pound, Australian dollar, and Japanese yen. In periods when the U.S. dollar declines in value as compared to the foreign currencies in which we conduct business, our foreign currency-based revenue and expenses generally increase in value when translated into U.S. dollars. We expect the percentage of total net revenue derived from outside North America to increase in future periods as we continue to expand our international operations.
Critical Accounting Policies and Estimates
Our consolidated financial statements are prepared in accordance with accounting principles generally accepted in the United States. The preparation of these financial statements requires us to make estimates and assumptions that affect the reported amounts of assets and liabilities and the disclosure of contingent assets and liabilities at the date of the financial statements and the reported amounts of revenue and expenses during the reporting periods. We base our estimates on historical experience and on various other
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