H264: tool for swapping frames without re-encoding?

[fvisagie]

Hi All,
One of the iPod H264 encodes I made from interlaced source has shuddery motion looking very much like incorrect field order handling.
I no longer have the source for this particular encode and am trying to find a fix after the fact.

No explicit interlaced handling was done during the encode (ffmpeg) and according to MediaInfo the output scan type is progressive. That means it won't be possible to fix the problem by changing output file field order. Even if I could find a tool for that; MPEG4 Modifier won't work with this file anyway.

Assuming that field order was initially incorrectly read, is there some tool with which I can swap frames in the progressive output file? Could something like Avisynth or VirtualDub be scripted to do that?

Many thanks,
Francois

[manono]

Could something like Avisynth or VirtualDub be scripted to do that?

You stipulated without reencoding, so the answer's no.

It probably can't be fixed anyway, even if reencoding's OK, if you've resized an interlaced source. With a sample we could provide more informed advice.

[jagabo]

I imagine it's theoretically possible to reorder frames (at least within a few frames) without reencoding an h.264 video but I don't know of any software that has this ability.

[fvisagie]

It probably can't be fixed anyway, even if reencoding's OK, if you've resized an interlaced source. With a sample we could provide more informed advice.

Quite so, for possibly yet another reason. Seeing the encode was neither explicitly deinterlaced nor interlaced, it probably decimated by using only every 2nd field (ffmpeg did complain about the container and video frame rates differing, 25 vs 50). In other words, the encode would have consistently used either Top Frame or Bottom Frame only, meaning field order maybe didn't come into the picture at all. Meaning the shuddery motion (only in high motion scenes) is probably due to missing picture information from alternate fields?

So having thought about it a bit more, this was probably a dumb question to ask in the first place .

[jagabo]

the encode would have consistently used either Top Frame or Bottom Frame only, meaning field order maybe didn't come into the picture at all. Meaning the shuddery motion (only in high motion scenes) is probably due to missing picture information from alternate fields?

Maybe. Take a look at the video in this post:

https://forum.videohelp.com/threads/307004-Best-framerate-conversion-%28eg-23-97-to-30-...=1#post1888926

If your source was telecined film you'll have one duplicate frame in every five frames. That causes a slight jerk 4 times a second.

[fvisagie]

Maybe. Take a look at the video in this post:

https://forum.videohelp.com/threads/307004-Best-framerate-conversion-%28eg-23-97-to-30-...=1#post1888926

If your source was telecined film you'll have one duplicate frame in every five frames. That causes a slight jerk 4 times a second.

Very illustrative sample video that.

Unfortunately I don't have the source to look at anymore. Here's an example of shuddering in the encode in case that sheds any light:

http://www.mediafire.com/file/zez0yuydy12/Shudder.mp4

[poisondeathray]

There's nothing wrong with the frame ordering in that sample. That's typical of a 25fps video with a camera pan of that speed.

If there is a frame ordering issue, it might be a playback/decoder issue on your end

If you were referring to the "juddery" look , and you source was interlaced, you could have bob-deinterlaced to 50fps with 2x the number of frames (instead of single rate deinterlaced to 25fps) , but I doubt your ipod supports those frame rates

Here is a simulation of what it would have looked like if you bob-deinterlaced to 50fps (I used avisynth and mflowfps to generate the "in-between" frames, as an example of frame interpolation)

[jagabo]

Shudder.mp4 is a normal 25 fps clip. It should display the normal jerkiness of 25 fps video. Another possible issue would be related to the refresh rate of your display. If it's 60 Hz the player will have to repeat frames to get 60 fps. Different repeat patterns can result in different types of jerkiness.

[fvisagie]

I'm a little surprised that this looks normal for that pan speed at 25 fps, but thanks very much for the reassurances. And for taking the trouble to demonstrate what deinterlaced encoding might have looked like, poisondeathray.

I've worked a lot with 25 fps video that remains interlaced from camera through DVD and I don't see this effect there even with faster panning. I guess it must be due to the "progressive" encode in this case throwing away half the frame information by just decimating.

I'll look into the iPod's maximum framerate, otherwise I'll just suitably deinterlace and compare results before deciding. Come to think of it, previously when I encoded home movies with panning etc. for computer display as opposed to hardware DVD, I did get good results with deinterlacing (and before anyone asks, my hardware DVD isn't progressive scan ).

Thanks very much again,
Francois

[poisondeathray]

I've worked a lot with 25 fps video that remains interlaced from camera through DVD and I don't see this effect there even with faster panning. I guess it must be due to the "progressive" encode in this case throwing away half the frame information by just decimating.

That's because your DVD player is effective bob-deinterlacing it to 50p upon playback. The interlaced PAL DVD is 25 frames per second or 50 fields per second

When you single rate deinterlace to 25p, you are throwing out 1/2 the temporal information. If you bob-deinterlace to 50p, you keep all the information (50 moments per second are represented)