I decided to re-ask this question to get a normal answer, and this time left everything in the archive link, study it and you'll understand what I'm talking about. The error is due to the fact that after changing one number in the header, the entire frame becomes incorrect (although the aspect ratio of 640x480 1:1 and 720x480 4:3 is the same).
Download: https://www.dropbox.com/s/xc9opzn3ujrfxlt/Bug%20in%20video.zip?dl=0
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It's not the same thing.
Changing the coded frame size is always problematic - it's not something you can do with a header or metadata edit. You need to re-encode in order to change the actual encoded frame size.
ie. Where do the extra pixels go ? In case you're bad at math, 720 is not the same thing as 640 .
Actual macroblocks make up each frame, you can't just discard some of them, because some are referenced in other frames; you should expect corruption
You can sometimes change the AR signalling, but the resultant effect is dependent on the playback application. Some may abide by the signalling and do something, or some ignore, or some do something entirely different. 720x480 4:3 might be resized to 640x480 on plaback in some applications, but in others they might resize to 720x540 . Both are 4:3 . (technically 640x480 is more correct)
Moreover, the quality of the resize depends on the algorithm used by the playback application. It might use a blurry algorithm, or it might use something sharp, or something super low processing but fast like nearest neighbor. -
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OK, I guess you are using MPGPatcher.exe, although I am only guessing, since you won't say for sure. I have used similar MPEG patching tools and there are some things you can change without re-encoding which will result in a perfectly valid MPEG-2 file. As poisondeathray has said, there are other things you can't change without causing problems.
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Yes wrong. It requires re-encoding
The resolution is the problem. You can't just add or discard pixels without re-encoding. The video relies on that data. Macroblocks from frames rely on other macroblocks from other frames when using temporal compression. If you reference an area that is "missing" you have corruption
You can signal 720x480 1:1 without re-encoding (DAR = 1.5) . That is what "square pixel" means. But then your AR is wrong , picture is distorted, objects too fat or wide
Why are you trying to do this ? -
If you're using avisynth for processing, that requires re-encoding anyways . It frameserves uncompressed video & audio.
Or did you mean just for preview / look development ?
There are no distortions in the original . If you meant how it displays the AR as "square pixel" - You can load original and resize in the script too. For example if you wanted 640x480 , square pixel, 4:3 DAR . You can choose which resizing method (e.g. maybe you wanted a sharper algorithm), instead of relying on player. -
Last edited by Megafox; 12th Feb 2018 at 18:20.
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In general, for DVD and cartoons, you need IVTC and resize to 640x480 . This requires re-encoding
IVTC is inverse telecine, to fieldmatch and decimate to recover the original film frames. The only reason it's like that in the first place was to make it compliant for DVD-video, you're just trying to reverse the process
But cartoons can be tricky, sometimes they have different effective fps sections (eg. sections with duplicates would be effectively ~12 fps) , other types of cartoons might have "video" sections with 59.94. But for most NTSC DVD cartoons, they should be 23.976p -
You can change the AR flag with MPGPatcher (or DVDPatcher, or a number of other programs). The frame size remains the same within the encoded file but it will be displayed with a different aspect ratio by the player.
I recommend you use the /all flag in MPGPatcher because there are many headers with the AR flag in an MPG file.Last edited by jagabo; 12th Feb 2018 at 18:32.
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