During high-power laser processing of metals, the amount of absorbed light is largely a result of vapor cavity geometry. This relationship has been established previously using ray-tracing simulations coupled with computational fluid dynamics models, but there has been no real-time experimental data that measures both absorption and keyhole shape directly. We simultaneously measure the keyhole shape and laser absorption by combining high-speed x-ray transmission imaging and integrating sphere radiometry during laser processing of Ti-6Al-4V solids and powders. The x-ray imaging is obtained at 50,000 frames per second while the integrating sphere collected scattered laser light every 40 nanoseconds. Under single spot illumination of a solid, correlation analyses of absorption with keyhole width, depth, and transverse keyhole area found that area most strongly correlates. Furthermore, we discovered that even under strong keyhole conditions rapid, microsecond dips in energy absorption of up to 25% resulted from short-lived collapses of the keyhole. Keyhole instability was also explored by introducing oxygen during laser processing, which caused prolonged keyhole collapses with a concomitant reduction in absorbed energy. Scanning the laser across the metal surface reveals that the keyhole has an initially high aspect ratio (near 3) for the first several hundred microseconds until a shallower steady state keyhole is achieved. This change in keyhole geometry is accompanied by a severe reduction in laser absorption of up to 35 %. When Ti-6Al-4V powder is introduced to replicate the laser powder bed fusion additive manufacturing (AM) process, this effect is again present. Similar changes in keyhole aspect ratios have been shown to occur during the AM process and cause porosity, but the effect of the highly localized increase in absorbed laser power has not yet been explored. As keyhole fluctuations are thought to contribute to porosity formation, monitoring of the scattered laser light thus appears promising for rapid, in situ detection. These results also demonstrate that absorption should be considered a dynamic quantity, even under nominally steady state conditions.