Interlaced video incorrectly handled

[Sharc99]

Rendering of interlaced video sources of format YV12 (4:2:0) or YV16 (4:2:2) to interlaced YV12 (4:2:0) using libx264 is flawed. There is significant chroma crosstalk/contamination between the fields, The functionality is essential for rendering captured interlaced VHS sources to interlaced YV12 h.264 video, for example. Setting the source file properties manually does not help / has no effect. Windows11, all Shotcut versions, including 22.12.21.

[ddennedy]

This was already fixed for the next version for which there is a beta that you can test.

[Sharc99]

Thanks. Will test soon. Shotcut is really great.

[Sharc99]

I made some test with beta 23.04.03.

• It works now for YV12 4:2:0 interlaced AVC (h264) sources.
• It still fails for lossless YUV 4:2:2 and 4:2:0 interlaced sources in .avi container, even though I set the input format (properties) accordingly (interlaced top field first).

[bmatherly]

I am willing to look into this if you can provide some test clips and instructions to reproduce.

[Sharc99]

Thank you for your kind offer. I stand corrected. The conversion works correctly for 4:2:2 and 4:2:0 sources with the latest Beta, so this is solved, thanks. I am just not sure whether the Preview and Sopes->Video Zoom show the scanlines and colors right for 4:2:2 .avi sources. I attach a testfile. The source properties have to be set manually to interlaced, top field first as the .avi does not provide the corresponding signalling. Export is h264 interlaced TFF which works correctly with the latest Beta., The fields of the h264 encode can be cleanly separated again as a test. So the main issue (chroma mingling between fields) of the previous version got solved. 0) 422i_.zip

[bmatherly]

I am just not sure whether the Preview and Sopes->Video Zoom show the scanlines and colors right for 4:2:2 .avi sources.

Make sure you uncheck "progressive" in the player settings.

The player always operates in 4:2:0. And the video zoom scope takes its values from the player. So the chroma samples will always be shared between 4 pixels in a box.

So if your source is 4:2:2, you will see some chroma bleeding in the preview/zoom scope.

[Sharc99]

The player always operates in 4:2:0. And the video zoom scope takes its values from the player. So the chroma samples will always be shared between 4 pixels in a box.

So if your source is 4:2:2, you will see some chroma bleeding in the preview/zoom scope.

This explains it. Thank you

[Sharc99]

There is another similar issue I like to report: The latest Beta of Shotcut processes interlaced 4:2:2 and interlaced 4:2:0 sources correctly, as discussed. However, when opening a virtual 4:2:0 interlaced .avi from the AVFS (Avisynth Virtual File System) the chroma is mingled between the fields as before. I am using the AVFS for opening Avisynth scripts (.avs) in Shotcut, because Shotcut cannot read Avisynth scripts directly. I am aware that this may be beyond the scope of Shotcut, but because the AVFS method works well with other video tools which do not directly read .avs scripts I thought I would bring this up as it may be I bug. Otherwise never mind.

[ddennedy]

That is not something in our control. It is somewhere between FFmpeg and AVFS.

[Sharc99]

maybe, yes.