How to preserve kCMFormatDescriptionExtension_FieldXXX after encoding?

I am currently working with AVAssetWriterInput with interlaced source.

I want to know the proper procedure to preserve 'fiel' format description extension through AVAssetWriterInput compression operation.

Do you anyone have an answer on this?


>>Technical Note TN2162

>>Uncompressed Y´CbCr Video in QuickTime Files

>>The 'fiel' ImageDescription Extension: Field/Frame Information


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What I have tried is following:


First decode into sample buffer with Field/Frame information

- Decode DV-NTSC source and get current FieldCount/Detail of source data

- Create a kCVPixelFormatType_422YpCbCr8 CVImageBuffer from source

- CMSetAttachments() kCVImageBufferFieldCountKey/kCVImageBufferFieldDetailKey with FieldCount=2/FieldDetail=14 to imageBuffer, same as DV-NTSC source

- CMVideoFormatDescriptionCreateForImageBuffer()

- CMSampleBufferCreateForImageBuffer()

- Now decompressed samplebuffer has kCMFormatDescriptionExtension_FieldXXX same as source


Second encode using ProRes422

- Next I create AVAssetWriterInput to transcode from _422YpCbCr8 into AVVideoCodecAppleProRes422

- Now AVAssetWriter can produce ProRes422 mov file, but it does not contain the format description extension 'fiel'.

- ProRes422 Encoder does preserve 'colr', 'pasp', 'clap' same as source, but no 'fiel' is there.


I have also tried to serve format description with kCMFormatDescriptionExtension_FieldXXX with initWithMediaType:outputSettings:sourceFormatHint:

but no success.

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I see this was several years ago, does anyone know a solution to this ?

How to preserve kCMFormatDescriptionExtension_FieldXXX after encoding?
 
 
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