The use case is very straight forward. Imagemagick is able to do the conversion but I want to do it with ffmpeg. Here is the all commands I have tried and all of them gives moov atom not found error.
ffmpeg -i /Users/ajitesh/Downloads/sample1.heif -c:v png -pix_fmt rgb48 /Users/ajitesh/Downloads/sample.png
Output
[mov,mp4,m4a,3gp,3g2,mj2 @ 0x7f85aa813200] moov atom not found
/Users/ajitesh/Downloads/sample1.heif: Invalid data found when processing input
it seems like moov atom is actually not present by trying to extract the location of moov atom using the following command
ffmpeg -v trace -i /Users/ajitesh/Downloads/sample1.heif 2>&1 | grep -e type:\'mdat\' -e type:\'moov\'
Output
[mov,mp4,m4a,3gp,3g2,mj2 @ 0x7f824c00f000] type:'mdat' parent:'root' sz: 2503083 420 2503495
[mov,mp4,m4a,3gp,3g2,mj2 @ 0x7f824c00f000] type:'mdat' parent:'root' sz: 2503083 420 2503495
FFmpeg does not currently support HEIF decoding (as of 2021-01-11).
Check the bug report #6521: HEIF support as FFmpeg development is active and the situation may change in the future.