Is it possible to capture video signal waveform as audio for video replay?
The short answer to your question is "no".  The sample rate of video is typically measured in MHz or GHz.  If you have a 1080p24 signal at 8 bits per pixel, the actual frame is 2750 x 1125 pixels (according to digital test equipment manufacturer Kramer).  Multiplied by a 24 fps refresh rate, this results in 74,250,000 pixels / second.  Multiplied by 10 bits per clock tick per pixel, this is a bandwidth of 0.74 Gbps.  As a "sample rate", that is approximately 1000x higher than 16-bit at 48K.  Hence the answer "no".