On Tue, Sep 29, 2020 at 11:29 AM Mark Filipak (ffmpeg) <[email protected]> wrote: > Oh, dear, that's what "packed" means? ...very misleading name, eh? How are > fields handled? Are the > pixels assumed to be unfielded (meaning so-called "progressive")?
So the topic of how interlaced video is handled in subsampled video is something we could spend an hour on by itself. In the Luma space, the Y samples are organized in interleaved form (i.e. lines of top/bottom/top/bottom). Because of chroma subsampling and the fact that multiple lines can share chroma samples, this gets tricky. In the simple progressive case for 4:2:0, you'll have the first Chroma sample corresponding to the first two luma samples on line 1 and the first two luma samples on line 2. If the video frame is interlaced however, the first chroma sample corresponds to the first two luma samples on line 1 and the first two luma samples on line 3. The first chroma sample on the second line of chroma corresponds with the first two luma samples on line 2 and the first two luma samples on line 4. This is known as "interlaced chroma" and a Google search will reveal lots of cases where it's done wrong and what the effects are. This is the article I usually refer people to: https://hometheaterhifi.com/technical/technical-reviews/the-chroma-upsampling-error-and-the-420-interlaced-chroma-problem/ The above article does a really good job explaining the behavior (far better than I could do in the one paragraph above). Devin -- Devin Heitmueller, Senior Software Engineer LTN Global Communications o: +1 (301) 363-1001 w: https://ltnglobal.com e: [email protected] _______________________________________________ ffmpeg-user mailing list [email protected] https://ffmpeg.org/mailman/listinfo/ffmpeg-user To unsubscribe, visit link above, or email [email protected] with subject "unsubscribe".
