Blur at bottom of video frame when BOTH chapters and subtitles are muxed.
Issue #72
invalid
When I use Subler to mux both SRT captions and a text chapter file into an MP4 video, I consistently get blurring across the bottom 1/16 of the video frame. If I reopen the file in Subler and remove either the caption track or the chapter tracks (text and images), the blurring goes away. I've repeated this across dozens of videos.
However, the blurring only appears under very specific conditions. It only occurs with SD video (for example, 640x360p), but not with HD video (1280x720p). And it is only visible in QuickTime for Windows, not in QuickTime for Mac, and not in other Windows video players (not even in iTunes for Windows, which I assume incorporates some version of QuickTime).
Any idea how to work around this? QuickTime is a fairly popular video player for Windows desktops, and perhaps the most popular Windows player that supports chapters and captions, so I'd like to be able to produce video content that's compatible with it. Also, I worry that the blurring indicates some nonconformity or incompatibility that could also be manifesting on platforms I haven't tested.
Comments (8)
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repo owner
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repo owner
You can upload it on dropbox or another service and send me the file link.
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repo owner
Looks ok here: https://www.dropbox.com/s/ewl0lqot9gbrnco/subtitles.png?dl=0
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repo owner
Oh I see. Maybe you should try with a width and a height that are divisible by 16.
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repo owner
Well it's not too hard to try to encode a video with a mod 16 resolution. Try 640 x 368 for example.
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repo owner
- changed status to invalid
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I didn't understand what you were asking for, in the width and height divisible by 16. I thought you meant frame aspect ratio, but you mean each pixel value for height and width. So I exported at 640x352 and found that the blur or row repetition did not occur (with 640x368 I got black bars at the top and bottom, so I wouldn't have seen the problem if it were present). That might explain why I don't see the problem in my 1280x720 files. But I don't understand why my 640x360 (which is a pretty common frame dimension) videos get this blur only when I mux both captions and chapters, and not when I don't mux either, or mux one but not the other. Can you explain, or point me toward an explanation? In particular, what could it have to do with the pixel dimensions being divisible by 16? Thanks.
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Okay, I did some research, and discovered there's this whole world of macroblocks I'd somehow managed to get this far without knowing anything about. I understand a little better what's happening now (though I still wonder why my problems only manifest when both captions and chapters are muxed into the file). And I see what my options are to eliminate the issue. Thank you again!
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Do you have a sample? By the way QuickTime Player 7 has been dead for years, not even iTunes uses it anymore. Vlc supports both chapters and subtitles too.