Different video when playing in reverse?

[sufr3ak]

I'm not sure how to even describe this. A friend gave me a copy of a video file he downloaded. When I watch it, the first 5-15 seconds are one set of a/v. But when stepping through backwards in avidemux, it shows what should be the original content.

The weird thing is in avidemux, is when stepping backwards, it keeps flipping between P frame, B frame, and even I Frame.

Actions to replicate:
1. Open Avidemux, drop file in
2. Play or or click forward through frames, it plays the undesired video.
3. If I click back frame by frame (or hold it), it shows the proper video.
4. If I play normal once clicking back into the undesired video, it plays the proper video.

I have some understanding of A/V, which is why my friend asked me for help. But I have no idea what I'm looking at.

[2nHxWW6GkN1l916N3ayz8HQoi]

Can you upload the problem video somewhere public?

[sufr3ak]

It's 2+GB, so im not sure where I can share it publicly. I'll send you a message with a link.

[johns0]

Thread moved to general discussions.

[sufr3ak]

Video Posted here: https://www.swisstransfer.com/d/0261adee-45b0-42da-93ab-0c471ae26d59

[davexnet]

I couldn't reproduce it but
the video seems problematic, with Avidemux giving Error: unable to advance to next key frame.

Opening the video in Virtualdub2 shows 30 fps, instead of the 60.x fps reported Avidemux, which seems bogus

Re-encoding in Vdub2 works well at the actual frame rate, although 24 fps is the true underlying frame rate for almost
the complete the show.
The only section where the true frame rate is 30 is the fox promo at the beginning

[sufr3ak]

I had a similar result in VLC. I will look into vdub2

[Alwyn]

In VDub2 for me, the video is badly out of sync later on. The IVTC filter appears to correctly remove the 5th duplicated frame but the audio sync is still way off.

I couldn't get any sense out of TFM/TDecimate in AVISynth.

[davexnet]

I set "audio skew correction" in vdub2 to -10000 and that seemed to fix the sync.
In case you haven't installed it, there is a recent update to vdub2

[jagabo]

Someone inserted a 10 second ad before the main show. The ad was 30p, the show was 60p. Timestamps for the show were not adjusted for addition of the ad. So the video timestamps run from 0 to 10 seconds then back to 0. This confuses editors and players.

[dellsam34]

In case you haven't installed it, there is a recent update to vdub2

Any direct link? Anything newer than 2.1.3.667?

[davexnet]

Hi dellsam, that appears to be the latest
https://github.com/v0lt/VirtualDub2/releases

[dellsam34]

This latest release is unstable, I couldn't open a DV file using it, So I went back to the last build which is much better.

[davexnet]

That's interesting, I had problems in the previous build with certain audio operations.
Perhaps you can log an incident at GitHub

[Alwyn]

I had problems in the previous build with certain audio operations.

Yes, I had trouble with Dellsam's multi-channel file that VDub 2.1 couldn't handle but VDub2 could. I made a post on Doom about it here and was given the runaround. I'm now back on the original VDub 2.0.

[dellsam34]

Not trying to derail the thread but on that issue I settled on using vdub2 with audio conversion, It takes several minutes for the resulting files from that commend that PDR gave me to load in AVSPmod.

[Alwyn]

I set "audio skew correction" in vdub2 to -10000 and that seemed to fix the sync.

Well done Dave, spot on. You must be a lip reader. I'm going to IVTC it and watch that file; seems like an interesting piece of history.

[sufr3ak]

1. I am truly humbled by how little I knew about video files. I thought I had a decent grasp, but wow, I am in the kiddie pool of this stuff.

2. Not sure if I'm doing this right, first time using Vdub2.

I go to Video > Filters>Add, scroll down to IVTC, click OK to accept defaults, OK again. (Does Save vs OK matter here?)

Then go to Audio > Interleaving, Delay audio track by -10000 and OK.

When I use "Preview Output From Start", it doesn't seem to have fixed the issue.

[Alwyn]

scroll down to IVTC, click OK to accept defaults, OK again. (Does Save vs OK matter here?)

For the IVTC filter, I'm using 'Reduce Frame Rate", "Auto" and "Adaptive". Then yes, just use Ok twice to get back to the main screen.

"Reduce Frame Rate" brings the framerate back to the source of 23.976 (actual source 24fps) by removing the extra frames inserted by the telecine.

When I use "Preview Output From Start", it doesn't seem to have fixed the issue.

I'm not sure what that actually does, but you can check the sync by playing any section (with the commentators talking).

I trimmed off the ad at the start using the black arrows next to the frame count window.

[sufr3ak]

Thank you. Did you have to re-encode it or were you able to just export it?

[Alwyn]

I did a re-encode. I got a "no can do" message when I tried to Direct Stream Copy it because I had applied the IVTC.

I did try a Direct Stream Copy for video and audio (with the audio offset by -10,000ms) and "export > stream copy" but the audio was out of sync.

[sufr3ak]

I tried to re-encode and it was 75% of the way through and was at 300 GB before I canceled it

[davexnet]

I tried to re-encode and it was 75% of the way through and was at 300 GB before I canceled it

Using vdub2?
That's because it defaults to uncompressed RGB Video (which is massive)
Up to you to set a specific output type at video/video compression

[jagabo]

vdub2... Up to you to set a specific output type at video/video compression

Video -> Compression...

[sufr3ak]

Yup, totally missed that setting. So it looks like I can cut off the start of the audio by moving it up 10 seconds, or retain some of the ad beforehand, but proper audio sync. Is that the same result for you all?

[Alwyn]

As I mentioned up a bit, I'd crop off the ad, then adjust the Audio>Interleaving>Audio Skew to -10000 (from Dave's post). Fine adjust that if required then Save Video...

See these guides on my site:

VDub Timeline editing

Saving/Exporting Video

[sufr3ak]

That's what I did, but it trimmed off some of the start of the audio and video. Just making sure I'm consistent in my result. Thank you for the guides, I'm always happy to learn more.

[Alwyn]

So it looks like I can cut off the start of the audio by moving it up 10 seconds, or retain some of the ad beforehand, but proper audio sync. Is that the same result for you all?

Yes, I moved the audio the -10000ms but the first words (I assume), "In 1914, the son of..." now come almost as soon as the video starts, in the middle of the ad. I did a Save Video and the rest is in-sync, so it looks like you'll have to accept the ad, or splice a segment from the titles into the start to replace the ad. Not sure that could be done in VDub easily.

[Alwyn]

This is what I came up with for the start using my NLE.

https://youtu.be/NhMJWJ_cJ7A