New submission from Stu-e <[email protected]>: Please can we have a libavfilter filter to implement double field rate interlace output in order to support graphics card interlace output with correct field order?
This is an idea taken from some MythTV discussion I read a while back. There is a way to maintain correct field order without relying on any field synchronisation signal from the video card. Currently 2 fields are presented to the graphics card frame buffer at the same time something like this: Frame A A B B C C D D Fields 12 12 34 34 56 56 78 78 Video t b t b t b t b (t=top field, b=bottom field) This is fine if the video stream (encoded with top field first) just happened to start just before the top video field is displayed. If the stream started when the bottom field was about to be displayed, field order would be incorrect with ugly consequences: Frame A A B B C C D D Fields 12 12 34 34 56 56 78 78 Video b t b t b t b t If instead 1 field was presented to the frame buffer per vertical sync, field order would always be correct: Frame A A B B C C D D Fields 12 32 34 54 56 76 78 98 Video t b t b t b t b or Frame A A B B C C D D Fields 12 32 34 54 56 76 78 98 Video b t b t b t b t What I propose is adding tinterlace to libavfilter and adding a new mode 5 to tinterlace that doubles the field rate as shown above. The new mode 5 would output 2 frames for every input frame. The first output frame would be a direct copy of the first input frame. The second output frame would consist of the top field of the second input frame and bottom field of the first input frame. The third output frame would be a direct copy of the second input frame, etc. This example assumes top field first: Input frame A A B B C C D D Input fields 12 12 34 34 56 56 78 78 Output fields 12 32 34 54 56 76 78 The most obvious use of this is to display a television video stream "as is" and let the television or flat panel decide on how and when to deinterlace. This is an alternative to power hungry pulldown detection and deinterlace schemes in a home theatre PC. ---------- messages: 12322 priority: normal status: new substatus: new title: Double field rate interlace filter (tinterlace new mode 5?) type: feature_request ________________________________________________ FFmpeg issue tracker <[email protected]> <https://roundup.ffmpeg.org/issue2314> ________________________________________________
