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I am currently using Kdenlive, but have also used ffmpeg when I have the simple task of adding audio to a video that does not yet have audio. Since it is just a matter of putting the video file together with the audio, it seems like it ought to be simple. Is there something about encoding mp4's that means it must take a lot of processing to complete?

I have good hardware (i7 6700k and gtx 1080), but kdenlive currently estimates 2.5 hours to complete adding audio to a 10 minute video.

Akami_Channel
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    It doesn’t take for ever, your doing something wrong. What is the command you are using? – szatmary Jul 31 '20 at 05:10
  • The command is needed as mentioned. Otherwise we can't provide any suggestions because we don't know what you're doing. – llogan Aug 01 '20 at 23:08
  • @llogan As mentioned, I was using Kdenlive, not ffmpeg that time. I will investigate further. Perhaps Kdenlive was only using 1 core, which might be the default. – Akami_Channel Aug 03 '20 at 20:32

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Without more info (encoder, settings, video width x height, instructions to duplicate the behavior, etc) we can only guess. It's probably re-encoding the video instead of only muxing it. Encoding is CPU intensive and takes a long time. Although 2.5 hours for 10 minutes seems excessive, but there is not enough info in the question to say why it takes this long.

If you want to add audio with ffmpeg see How to add a new audio into a video using ffmpeg? This will allow you to mux the video (and optionally the audio) without encoding it: like a copy and paste.

llogan
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  • I suppose it is a Kdenlive bug, because I just did it with ffmpeg and it took about 90 seconds, while trying to render it with Kdenlive says it will take an hour and 43 minutes. When just adding audio to a clip, I will stick with ffmpeg at the command line then. – Akami_Channel Aug 03 '20 at 21:32