Unable to decode H.265 alpha channel file with YUV400 format

[cylindrical2002]

png00001.zip

Description

I'm trying to decode H.265 files that contain alpha channels. While the main color video file (YUV420P format) decodes successfully, the alpha channel file fails to decode with error code 0x3d4.

Steps to Reproduce

1. Encode two H.265 files:
   • Main color file (png00001.h265) in YUV420P format
   • Alpha channel file (png00001_alpha.h265) in YUV400 format
2. Create config file png00001_alpha.cfg:

--input png00001_alpha.h265
--output png00001_alpha.yuv
--save_output 1
--num_frames -1
--chroma_format YUV_420P
--share_display_buf 0
--max_wd 770
--max_ht 200
--max_level 51
--num_cores 4
--loopback 0
--display 0

3. Run decoder:

./hevcdec png00001_alpha.cfg

Current Behavior

The decoder fails with the following output:

Ignoring argument :  --max_wd
Ignoring argument :  --max_ht
Ignoring argument :  --max_level
Ittiam Decoder Version number: @(#)Id:HEVCDEC_production Ver:05.00 Released by ITTIAM Build: Feb 12 2025 @ 13:03:56
FrameNum:    1 TimeTaken(microsec):      3 AvgTime:      3 PeakAvgTimeMax:      0Output:  0 NumBytes:    794 
Error in video Frame decode : ret 3d4 Error 0
Summary
Input filename                  : png00001_alpha.h265
Output Width                    : 0   
Output Height                   : 0   
Bitrate @ 30 fps(mbps)          : 0.21  
Average decode time(micro sec)  : 3     
Avg Peak decode time( 8 frames) : 0     
FPS achieved (with format conv) : 333333.33

Expected Behavior

The decoder should be able to handle YUV400 format files, which are commonly used for alpha channels in H.265 video coding.

Environment

• OS: macOS
• Compiler: Clang
• Build: Feb 12 2025 @ 13:03:56
• libhevc version: 05.00

Additional Context

The main color file in YUV420P format decodes successfully with the same configuration (except for the input/output file names). This suggests that the issue is specifically related to the handling of YUV400 format in the alpha channel file.

Questions

1. Does libhevc support YUV400 format for alpha channel decoding?
2. If not, what is the recommended way to handle alpha channels in H.265 files?
3. Is there a workaround available, such as encoding the alpha channel in YUV420P format?

[harishdm]

Does libhevc support YUV400 format for alpha channel decoding?

No. libhevc currently doesn't support YUV400 files.

If not, what is the recommended way to handle alpha channels in H.265 files?

No way to handle alpha channels coded as YUV400 using libhevc at the moment.

Is there a workaround available, such as encoding the alpha channel in YUV420P format?

If alpha channels can be coded in YUV420P (with chroma set to 128), that can be decoded by libhevc.

[cylindrical2002]

Thanks for the quick response!

Just to clarify, is there any chance libhevc will support YUV400 in the future? If not, I’d be happy to help out by adding this feature myself. Would it be possible to submit a pull request for this?

Also, if I decide to proceed with modifying the code to support YUV400, do you have any suggestions on how to best approach this?

[harishdm]

Just to clarify, is there any chance libhevc will support YUV400 in the future?

this is currently in review internally and as and when it is approved we would be adding the support for the same.

[cylindrical2002]

I’m glad to hear that support for YUV400 format is under review. Since our company is working on a related project, it would be extremely helpful for us to know if there is any estimate on when the support for YUV400 might be added to libhevc. Do you have a rough timeline for when this feature could be available?

If it's not too much trouble, we’d appreciate any further insights on the current status or plans for this feature.

Thanks again for your help!

[harishdm]

Unfortunately we do not have a timeline that we can commit to at the moment. It all depends on the internal review discussions about the need for YUV400 and its feasibility.

[harishdm]

@cylindrical2002
libhevc now supports YUV400 format.

Can you please try the following?

$ ./hevcdec -i ~/Downloads/png00001/png00001_alpha.h265 -o png00001_alpha.yuv --num_frames -1 --save_output 1  --enable_yuv_format 1 --chroma_format GRAY

Please note, YUV400 support is just added and may need some more updates (especially with odd dimensions).