I read the tutorial and opened the DSM7 folder's read/write permissions. But it still can't play normally, please help me
embyserver (3).txt
ffmpeg-transcode-c0903779-a44d-4cd8-92a8-a3c4b3fa0785_1.txt
This is a known issue, and you are correct with the above. It's fixed in the beta and it will be fixed in the 4.8.x released.
Unfortunately, the fix cannot be backported to 4.7.x because there were fundamental changes since then.