mdls command gives “null” in output

All,

I have shell script that loops recursively through a given folder and generates a metadata report for media files using the mdls command.. The code works most of the time, but sometimes I get null as the output for some media files. Here is my script which finds all m4v files in a given folder and outputs the metadata information for each file found.

cd "path_to_folder"
while IFS= read -r -d $'\0' file; do

mdls "$

file

echo -e "===================================\n"

done < <(find .  \( -iname \*.m4v \)  -print0 )

The output sometimes doesnt include complete info for the files. I dont see kMDItemPixelHeight, kMDItemPixelWidth, kMDItemKind etc in the output. Here is a sample output that's missing most of the info.

kMDItemFSContentChangeDate = 2012-04-03 05:45:24 +0000

kMDItemFSCreationDate = 2012-04-03 05:45:24 +0000

kMDItemFSCreatorCode = ""

kMDItemFSFinderFlags = 0

kMDItemFSHasCustomIcon = 0

kMDItemFSInvisible = 0

kMDItemFSIsExtensionHidden = 0

kMDItemFSIsStationery = 0

kMDItemFSLabel = 0

kMDItemFSName = "video1.m4v"

kMDItemFSNodeCount = 2328812

kMDItemFSOwnerGroupID = 20

kMDItemFSOwnerUserID = 501

kMDItemFSSize = (null)

kMDItemFSTypeCode = ""

=============================================================================

If I run mdls command from the terminal for the video1.m4v, it displays complete info for the file. What am I doing wrong? Is it some spotlight related issue?