I have a 1920x1080, 29.97, interlaced, upper, 1.0 sequence. Embedded in that sequence are some 720p, 59.94 clips (yes, I know that's not the best thing to do here, but let's assume that it needs to be this way).
I exported to a .mp4 file using the H.264 export format with the HD 1080i 29.97 preset; 2-pass VBR; max render quality. Then I exported to a .m2t file using the H.264 Blu-ray export format with HD 1080i 29.97 preset; audio muxed; 2-pass VBR; max render quality. When I play back the .mp4 file in Windows Media Player the video looks poor, especially where there is motion; kind of looks like jagged lines similar to what I saw when I recently exported SD interlaced footage in a progressive sequence. But when I play the .m2t file it looks ok. I pulled both exported clips back into PP and they have the same characteristics when I mouse over. Let me know if you want screen shots or sample video clips.
I would have expected these to looks the same, but then maybe I don't understand the difference between these formats. Feedback?
Despite the Interlaced UFF export setting, the H.264 option doesn't respect that and exports out a poorly deinterlaced progressive video instead.
If you need interlaced H.264, always use the H.264 Blu-ray option.