Towards Better Chroma Subsampling - SMPTE Presentation Notes
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Inappropriate mixing of resampling schemes

Most non-linear editing programs render only segments that have effects on them. For a cross dissolve, only the cross dissolve is rendered; the clips on either side not in the transition are not rendered and thus less rendering is needed.

If the material has undergone chroma subsampling, this means that there is a jump from 1st generation to 2nd generation to 1st generation. The box and nearest neighbour resampling schemes "pass through" the chroma, so there is no generation loss. Therefore the jump between 1st and 2nd generation is not noticeable.

1st generation (roll-over to see 2nd generation).	2nd generation.

This scheme tends to backfire if:

• Dealing with multiple chroma formats on the same timeline... e.g. 4:4:4, 4:2:2, 4:1:1
• Exporting to 4:4:4 formats (e.g. 4:4:4 JPEG) and chroma formats that differ than the acquisition format.
• Up and downconverting material in the timeline