No documentation on availability of kVTDecompressionPropertyKey_FieldMode

Originator:aman
Number:rdar://30561783 Date Originated:
Status:Open Resolved:
Product: Product Version:
Classification: Reproducible:
 
Area:
Core Video

Summary:
According to the documentation, the various kVTDecompressionPropertyKey_FieldMode and kVTDecompressionPropertyKey_DeinterlaceMode flags are "optional property for video decoders to implement".

When I attempt to use this on macOS Sierra, no deinterlacing is performed.

Are these deinterlacing options supported by macOS or iOS? Is there any information available about which OS/devices support these decoder options? Or any way to determine if a specific piece of Apple hardware does or does not support deinterlacing in the decoder?

Steps to Reproduce:
1. Use VTDecompressionSession with kVTDecompressionPropertyKey_FieldMode and kVTDecompressionPropertyKey_DeinterlaceMode options

Expected Results:
Expect deinterlaced output

Actual Results:
Output is not deinterlaced.

Version:
iOS 10

Notes:
I tried all the various decoder options, including using kVTDecompressionProperty_FieldMode_DeinterlaceFields and kVTDecompressionProperty_DeinterlaceMode_Temporal, along with kVTDecodeFrame_EnableAsynchronousDecompression | kVTDecodeFrame_EnableTemporalProcessing. None seem to be able to produce deinterlaced output.

Configuration:
macOS Sierra and iOS 10

Comments

I looked at the documentation again and found VTSessionCopySupportedPropertyDictionary(), which I was able to use to verify that VTDecompressionSession on my macbook supports FieldMode. The same call on iOS does not list FieldMode. 

FieldMode =     {
    PropertyType = Enumeration;
    ReadWriteStatus = ReadWrite;
    SupportedValueList =         (
        DeinterlaceFields,
        BothFields
    );
};

However, the DeinterlaceMode property is not listed so I don't know which options are valid to use with that property.

Further, when I try to decode H264 video that is interlaced (with MBAFF coding) after setting FieldMode=DeinterlaceFields, the decoded image data is not deinterlaced as I would expect.

Here is a sample video file which does not get deinterlaced with a VT decompression session: https://s3.amazonaws.com/tmm1/videotoolbox/interlaced.mp4

By aman at Feb. 23, 2017, 6:02 p.m. (reply...)

Apple Developer Relations

Engineering has determined that this issue behaves as intended based on the following information:

First, determining if kVTDecompressionPropertyKey_FieldMode is supported: Call VTSessionCopySupportedPropertyDictionary. If this key is in the returned dictionary, it is supported with the decoder, and we would expect setting kVTDecompressionProperty_FieldMode_DeinterlaceFields to produce deinterlaced results.

In general, this is supported on macOS for DV content and H.264 content. Please give this a try and let us know if deinterlace doesn’t work in a case where the VTDecompressionSession implies that it should (via the SupportedPropertyDictionary). In such a case, providing an example of content that demonstrates the issue would help.

By aman at Feb. 23, 2017, 6:01 p.m. (reply...)

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