PNGs most of the time are compressed, depending on the actual image content the compression ratio and thus the performance needed to decode the frames varies. (Try for example saving an image that is single-colored vs. one that contains 100% noise). The CPU might not be able to cope with decoding that many frames.
When on the other hand the images are not compressed (or not that much) you’ll may have run into another problem: the speed of your SSD. A decent single SATA SSD should yield about 500 MB/s read speed.
If your images were totally uncompressed the player would have to load about 734 MB/s as Sune already calculated. Which is nearly 1,5 times more than your SSD can most likely deliver.
The Player (EX9.Texture) node has two output pins Duration IO and Duration Texture. Connect each of those outputs to an add-(value-spectral) and compare the results. Both results added together will give you the total loading time, which should not be greater than 1/60 or 1/50 depending on the desired renderer framerate.
If the IO-Duration is the bottleneck you have to increase the loading speed. Which can be achieved for example by putting 2 or more SSDs in a RAID0 configuration or a Windows Stripe Volume. Up to a certain point (e.g. max speed of your sata or raid controller) the read speed increases linearly so two SSDs should give you a read speed of about 1000 MB/s.
If the Texture Duration is the problem you might need a faster processor and / or a faster GPU…
Just as a side note:
I rencently also ran into a performance problem with Player (EX9.Texture) using a rather powerful PC. (Intel Core i7-5820K, 3.300 MHz, Sapphire 4GB HBM R9 NANO, 4 SSDs in Raid0). Even though the combined loading time was nowhere near the time needed for calculating one frame (1/50), the framerate always dropped. I tested a lot of different filetypes/formats and only a combination of tga (textures with alpha) and jpg (no alpha) (if barely) worked out. DDS in various formats didn’t work at all though according to the player decoding time was virtually 0 and loading time also negligible.
When doing some “cross-tests” with a (proprietary) DX11 player there were no perf problems at all.
Unfortunately there was no time to test an equally powerful nvidia card.