Old 12-15-2018, 07:15 AM   #1
lilith93
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Default Rendering Video but leaving Audio untouched

I have a video of which I want to change the aspect ratio. The problem is when I render the video in Reaper I get crackles and strange artifacts, depending on the export settings of the audio. I'm on Linux and use ffmpeg for converting the video.
Audio codec AAC in not working very well, I get better results with MP3 or 24bit PCM.

Is it possible to leave the audio trace unchanged and only render the video?

edit: Can a mod move this to https://forum.cockos.com/forumdisplay.php?f=54 please?
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Old 12-15-2018, 12:24 PM   #2
Eliseat
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Its always better to separate (demux) video and audio before editing in Reaper as Reaper can't leave video or audio alone if joined together. mkvToolnix is a good option. Its quick and easy to separate the files and you can place video and audio on different tracks in Reaper then. But this only works if you don't mess with time and tempo.

Another method would be to render two times. One only the video. One only the audio in the preferred format. Then join them externally with mkvtoolnix.
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Old 12-15-2018, 01:00 PM   #3
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Cool, thanks! There's also a linux version of this tool.
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Old 12-15-2018, 01:15 PM   #4
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You might need to ensure that your encoding at the same framerate you started with. There are tools for this but in Reaper the framerate is set in project preferences.
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Old 12-16-2018, 07:24 AM   #5
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Quote:
Originally Posted by foxAsteria View Post
You might need to ensure that your encoding at the same framerate you started with. There are tools for this but in Reaper the framerate is set in project preferences.
Does this affects audio also?
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Old 12-16-2018, 08:25 AM   #6
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No, its about later joining video and audio together. If you change the frame rate from original video it could lead into tiny time changes which then make the audio asynchronous.

But that's all assumption as we have no idea what you are doing there. If audio and video don't have to be synchronous its not too important. You could practically join (mux) every audio and video with the same length.
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Old 12-16-2018, 08:42 AM   #7
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Ok, I see. I recorded a video made with lebiniou (www.biniou.net) with simplescreenrecorder:

https://www.youtube.com/watch?v=6DcsqBRBIew

After recording it I wanted to adjust the size of the video to 1280:720, which I did with reaper using ffmpeg. The problem was, that with some codecs the sound was crackling at some positions. ffmpeg executed in a terminal can also merge the original audio with the resized video. I guess the same can be done with mkvtoolnix, which I will try the next time.

At least now I'm aware of all the problems I can run into. Thanks again.
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