After using mp4encrypt to encrypt an MP4 file with MPEG-CENC, the video cannot be played by dragging the progress bar.

[cderfv1]

The source video needs to be a fragmented MP4 file. so first I convert mp4 to a fragmented file.mp4fragment：
./mp4fragment --index /mnt/c/test/zhz1.mp4 /mnt/c/test/zhz1-f.mp4

then：
./mp4encrypt --method MPEG-CENC --key 1:a0a1a2a3a4a5a6a7a8a9aaabacadaeaf:0123456789abcdef --property 1:KID:121a0fca0f1b475b8910297fa8e0a07e --key 2:a0a1a2a3a4a5a6a7a8a9aaabacadaeaf:aaaaaaaabbbbbbbb --property 2:KID:121a0fca0f1b475b8910297fa8e0a07e /mnt/c/test/zhz1-f.mp4 /mnt/c/test/zhz1-cenc.mp4

After dragging the progress bar, it will play for a long time. It looks like it's must decrypted from the first frame until the current frame.

I find the difference between the encrypted stream's sidx and the clear stream is very large.

HELP！

[cderfv1]

why mp4encrypt required source video needs to be a fragmented MP4 file？