The file boot.emmc.win is a raw partition backup created by Team Win Recovery Project (TWRP). It is essentially a boot.img file that has been renamed by the recovery software during the backup process. Understanding the File Formats
mv boot.emmc.win boot.emmc.win.gz gunzip boot.emmc.win.gz mv boot.emmc.win boot.img boot.emmc.win to boot.img
Rename the Extension: The simplest method is to manually change the file extension from .win to .img. Example: Rename boot.emmc.win to boot.img. The file boot
Several scenarios require this conversion: LZ4 magic: 04 22 4D 18 LZO/others vary
mv boot.emmc.win.copy boot.img
sudo apt install android-sdk-libsparse-utils android-sdk-ext4-utils mkbootimg
04 22 4D 18A very specific and technical topic!
If you want to be 100% sure the file is valid before flashing: Check File Signature : Use a hex editor or the