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Old 06-29-2020, 09:10 AM   #1
nepenthe
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Default All imported mp4/mov begin with short blank space

Every time a client sends me a reference video (usually MP4 / MOV), it loads in Reaper with a very small segment of blank audio/video before the start of the video. It’s about a frame or less, 1500 samples in the attached screenshot. So, in the Reaper timeline, the audio in the reference video is not in sync with audio exported from their NLE if you line up the media item starting points. (see screenshot)

This is a bit of an issue since it causes the reference video I’m given to be out of sync with the client’s NLE timeline by a small amount. So if I have finished the mix, then select the reference video, set selection to item, and render the new mix to be the same length as the reference video, the new audio will actually be out of sync when the client loads it - it will be slightly early.

Also, it creates problems when mixing and editing since the exported audio is out of sync with the video until I re-align the two.

Just curious what’s up with this and if it can be fixed. Thanks!
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Old 07-07-2020, 07:49 AM   #2
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bump. This is a consistent issue for me and I’m still hoping to hear from someone on the dev team re: what’s going on here. Thanks a bunch.
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Old 07-07-2020, 08:00 AM   #3
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There was once a similar problem but got solved. It was a short blank screen at the end. But you also should consider that this could be a problem with the player, because Reaper just uses VLC or ffmpeg for this.

Last hint: Post your problem in the video section of this forum, maybe there are people who have the same problem or know how to solve it.

greetings
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Old 07-07-2020, 08:27 AM   #4
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Quote:
Originally Posted by Eliseat View Post
There was once a similar problem but got solved. It was a short blank screen at the end. But you also should consider that this could be a problem with the player, because Reaper just uses VLC or ffmpeg for this.

Last hint: Post your problem in the video section of this forum, maybe there are people who have the same problem or know how to solve it.

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Ah thanks :-)
I’m not sure if this also happens on VLC. I’ve only checked on other DAWs and audio editors which can extract audio from video.
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Old 07-12-2020, 05:49 PM   #5
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But I’m not really video editing. Just doing audio post on Reaper. No one from Cockos is going to weigh in on this? I checked online and don’t see an official way to obtain support for Reaper aside from this forum. Im still not sure if this is user error on my part or what since it seems like a really obvious issue that many post editors would be asking about. I’d just like to know what’s up.
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Old 07-12-2020, 10:48 PM   #6
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Why don't you line up the starting points manually? For me this looks like an exporting issue rather then interpretation issue in Reaper.

To make it clear: your client sends you a video (with audio) from a concert and a separate mix (only audio) from that concert. You have to master the mix and send it back so they can put it together to a new video with your mix.
What source program are they using?
Could it be that the tiny amount of shifting has to do with a frame rounding of the source software? Imagine that video has to follow frames. Audio not. So if someone cuts a video in a DAW it cuts thru video as if its audio. But that's not the case. The program has to start the video with a frame even if the item starts at a different point.
To check this you should change the measuring from beats to frames in the source program and take a look if the item really starts with a frame. Hope you can follow me because my English lacks.

That's just a theory.

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Old 07-13-2020, 02:46 AM   #7
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Most of my clients use Premiere Pro. Generally they give me the audio they want me to fix up either by soloing this audio and exporting a WAV or exporting an AAF or OMF. Then they send me a copy of their video with the rough audio mix for reference and sync purposes.

When these items are loaded in Reaper the reference video is always off by a frame or so. The timecode in reaper is not a mirror of the time code in their project. Thus it’s not an accurate representation of the client’s timeline. The audio files are accurate so I leave them as-is and shift the video contents to sync with the audio.

There is another scenario which is like a typical super short-turn YouTuber workflow where I just get a video (mp4) and have to extract the audio to perform repairs. If I extract the audio in iZotope RX, restore and save edited audio as WAV, then load this into reaper for mastering and Re-rendering the video, I’ll have to manually realign the audio even though I haven’t changed the length at all. Because when reaper loads the video it inserts that extra frame, but iZotope does not. So that’s two scenarios where this issue happens. Although in reality it happens on Almost every post project.

As far as your question about aligning starting points manually - this is what I do but not by choice. :-)
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Old 07-13-2020, 03:08 AM   #8
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Hm. I would suggest to not re-encode the video but instead muxing video and audio in an external program without any loss. The question is: what happens in your workflow, what leads into the problems? You mean this also occurs if you load a mp4 video from Youtube with extracted audio? I'm not sure, what you mean.

For example: I could load a video from youtube, demux the audio with mkvtoolnix and load both, the video (with original sound) and the extracted audio, into Reaper. In your case, if both items start at the same point, the video/audio should be shifted. Right? If yes, I could try this myself to reproduce it.
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