This paper investigates how authentic web-delivered video can inform ESL online instruction and enhance the incidental acquisition of vocabulary and listening comprehension. A total of 24 adult learners of English as a Second Language enrolled in a listening comprehension class at a major Midwestern university participated in the study. The participants completed pre-, post-, and delayed vocabulary post-tests, a computer-assisted language learning (CALL) activity including an academic lecture on horticulture, and a questionnaire. In addition to the performance measures, a screen capturing application, Camtasia Recorder (2001), was used for nine learners to document actual learner-CALL activity interaction, which was used as the basis for a post-task interview. The results suggest that incidental vocabulary acquisition occurs and that lower-level learners are more likely to resort to the wrong aspects of the lecture in responding to comprehension questions. While engaged in the online CALL activity, advanced learners exhibited both metacognitive and cognitive learning strategies. Intermediate and lower-level learners mostly made use of cognitive strategies. Female learners used more strategies than male learners and female learners preferred cognitive strategies while male learners used more metacognitive than cognitive strategies.