Hang on emlx files

[prohtex]

I'm working on a directory catalogue application, and have thus far been using qlmanage to produce thumbs. As far as I can tell, qlmanage doesn't support defining image output type from the command line, and I need jpegs, not pngs. I could pipe the png to imagemagick but I'd rather not do that for performance reasons. I was happy to find this wrapper and have been using it quite a bit. I am sending lots of files of all types, and it works as expected.

Today I encountered an issue with .emlx files. These seem to be the only files that create this issue. qlmanage can generate a thumbnail instantly without issue, but ql-thumbnail hangs for a few seconds, then fails to create the thumbnail file.

For example,
qlmanage -t -f 4 -o . 22221.emlx
produces a png, 22221.emlx.png, 512 pixels with the appropriate preview image

The same operation with ql-thumbnail fails without any output
ql-thumbnail 22221.emlx . public.png 512 512

I've tried public.png and public.jpeg without success. Any help is much appreciated!

[ingve]

The ql API functions do not return a lot of useful info. I've added some minimal error reporting in #3, could you try that and see if an error message is printed in your terminal?

[prohtex]

initial testing of quality flag looks great, thanks!

host:Desktop user$ ql-thumbnail-lossy test_source.png test.jpg public.jpeg 512 512 .95

host:Desktop user$ exiftool test.jpg
ExifTool Version Number : 10.46
File Name : test.jpg
Directory : .
File Size : 37 kB
File Modification Date/Time : 2017:06:21 16:57:38-07:00
File Access Date/Time : 2017:06:21 16:57:41-07:00
File Inode Change Date/Time : 2017:06:21 16:57:38-07:00
File Permissions : rw-r--r--
File Type : JPEG
File Type Extension : jpg
MIME Type : image/jpeg
JFIF Version : 1.01
Resolution Unit : None
X Resolution : 72
Y Resolution : 72
Exif Byte Order : Big-endian (Motorola, MM)
Exif Image Width : 512
Exif Image Height : 288
Current IPTC Digest : d41d8cd98f00b204e9800998ecf8427e
IPTC Digest : d41d8cd98f00b204e9800998ecf8427e
Image Width : 512
Image Height : 288
Encoding Process : Baseline DCT, Huffman coding
Bits Per Sample : 8
Color Components : 3
Y Cb Cr Sub Sampling : YCbCr4:2:0 (2 2)
Image Size : 512x288
Megapixels : 0.147

emlx files generate this error:

host:Desktop user$ ql-thumbnail-lossy 22221.emlx test.jpg public.jpeg 512 512 .95
Error generating thumbnail

host:Desktop user$ ql-thumbnail-lossy 22221.emlx test.jpg public.jpeg 512 512 1
Error generating thumbnail

host:Desktop user$ ql-thumbnail-lossy 22221.emlx test.jpg public.jpeg 512 512
Error generating thumbnail

host:Desktop user$ ql-thumbnail-lossy 22221.emlx test.png public.png 512 512
Error generating thumbnail

qlmanage for the same emlx file works fine:

host:Desktop user$ qlmanage -t -f 4 -o . 22221.emlx
Testing Quick Look thumbnails with files:
22221.emlx

• /Users/user/Desktop/22221.emlx produced one thumbnail
  Done producing thumbnails

host:Desktop user$ exiftool 22221.emlx.png
ExifTool Version Number : 10.46
File Name : 22221.emlx.png
Directory : .
File Size : 36 kB
File Modification Date/Time : 2017:06:21 16:58:16-07:00
File Access Date/Time : 2017:06:21 16:58:19-07:00
File Inode Change Date/Time : 2017:06:21 16:58:16-07:00
File Permissions : rw-r--r--
File Type : PNG
File Type Extension : png
MIME Type : image/png
Image Width : 384
Image Height : 512
Bit Depth : 8
Color Type : RGB with Alpha
Compression : Deflate/Inflate
Filter : Adaptive
Interlace : Noninterlaced
SRGB Rendering : Perceptual
Image Size : 384x512
Megapixels : 0.197

[prohtex]

If you'd like, I can send you the emlx files in question, but I'd rather not post here

[ingve]

I don't use emlx files, do you know if it is a built-in QuickLook generator from Apple, or a third-party quicklook plugin?

[prohtex]

emlx files are just emails. According to

qlmanage -m plugins

emlx files are handled by Mail.qlgenerator

com.apple.mail.emlx -> /System/Library/QuickLook/Mail.qlgenerator (3273)

I can't imagine why qlmanage can make the thumb but not ql-thumbnail!

[prohtex]

I looked over the list of the qlgenerators and tried a few other exotic filetypes - .xls, .ics, .webarchive, .epub and all worked fine. I'm less concerned with having thumbs for a bunch of emlx files and more interested in the root of the problem in case there are other filetypes that are not being generated.

[ingve]

Are the file permissions different on the emlx files, or are the owner/access attributes also the same? Any relevant output in the system log (viewable via Console.App)?

[prohtex]

I double checked and not a permissions issue. No console output.

[ingve]

Thanks for checking. As mentioned previously, I don't use emlx files, but when I tried with a test file from another open source project, the call to QLThumbnailImageCreate failed (returned NULL), which according to the docs happens "if Quick Look does not support this file type". However, as you've already demonstrated, qlmanage is able to generate a thumbnail image for the emlx file.

I will leave this issue open. Please file issues if you encounter other file types that are not supported. I have updated ql-thumbnail to return EXIT_FAILURE if it is unable to generate a thumbnail, so you should now be able to check the exit status and use another program for the (hopefully few) files it cannot handle.

[prohtex]

Thanks. I've encountered quite a few oddities with qlmanage. For example, my admin user account seems to have different qlgenerators loaded than the root user. If I want to make thumbs for audio files (mp3, m4a, m4b), only root seems to be able to do this. On the other hand, there are other filetypes the root user cannot generate. Very weird.

[peters128]

Hi Ingve,
your code about ql-qlthumbnail is cool, I tried it, it's working well. But I have a problem here. I have a big project using standard C++, and I'm trying to use the native MAC API to generate thumbnails, so this "ql-thumbnail" is a perfect sample, I ported most of the code into my project. but for some reason it's not working. the "QLThumbnailImageCreate" call always returning "null". I tested it on MAC Catalina, so I firstly doubt it's the "SIP" problem, so I disabled the "SIP" on my Mac, but the problem is still the same. I can't find any related error information in the system log. The apple doc is saying if the function does not support input format, it'll return null, my input file is a ".png" file and output is a ".jpg" file, the "ql-thumbnail" works well to produce the thumbnail, so it's not the reason of "file format is not supported".
Do you have any idea what is happening ? Do you know where can I find the error information about those API calls ?

Thanks in advance!

Peter