When loading an image sequence to the "Movie Clip Editor", click on the first image that you want to load (in our case here at "0001.jpg" and then on "Open Clip":
Selecting everything with "a" has no effect. On my first try, I had clicked on image #300 and then marked everything with "a" but this loaded only that last image of the sequence.
Hi, I just tried it on my Blender 2.91.2 (win x86_64), I can A select all 1800 images under a folder.
May be there's something wrong on your side?relidin Selecting everything with "A" was also possible in my case as described in the last two sentences of my post above, but this was irrelevant for the "Image Sequence" loading. What counts is the image onto which you click directly. When loading an image sequence, Blender also loads all images of that sequence with higher numbers than the image that you have selected directly by clicking onto it.
Sorry, didn't understand your question clear enough.
I checked it again and found "Open Clip" button takes directory path as input.
Which means no matter which image(s) you choose, it will always load all images under that folder.
I've tested it with Blender 2.92 Alpha again. The sorting order obviously matters. If you click onto "Name" so that you get a sorting order with descending indices and then select an image, you get automatically loaded all images with higher indices as well:
If you select everything with "A", you get only the image with the highest index.
Now, change the order to ascending indices and repeat the same. Selecting one image also loads all images with higher indices but selecting everything with "A" now selects all images. You could alternatively only select the image with the lowest index and this would load all images as well.
So, selecting everything with „A“ works like selecting the top entry of your images after sorting them by their indices.