I’m not sure of the motivation for this ‘unfolded’ tensor. The data is 99.5% redundant, and the 200-sample window can be created at train-time from the audio-data tensor. Just take a slice audio[i:i+200] of the 8m audio tensor, and audio[i+201] as your target.
The only extra ingredient, then, is the set of offset indices into your audio data, which you could sample randomly or sequentially.