How To Keep Original Audio On Newly Recoded Video

Hello there.

I load a video in VideoReDo to lower the width by height resolution and the amount of kbps, in order to shrink the video file and for it not to lag when fastforwarding/rewinding the video on the computer. But mainly to shrink its size and keep almost the perfect quality as the original.

So I go to the "Save Video As" screen, and do what I gotta do in there for the settings. Yet for this one video that I'm trying to recode, I recode it, then it completes. Then I open the video file and the audio apparently starts glitching from minutes 6:00 till 30:00 or whatnot. I tried changing up the settings again, yet the same thing happens.

So I'm aware of a different app that I use which lets you keep the original audio source of a video file. How can I do that in VideoReDo?



Staff member
The audio won't be touched in VideoReDo unless you ask it to. However, if there are issues with the source video such as missed frames, audio frames may be dropped in order to keep sync with the dropped video frames. Where there any dropped or audio or video frames in the output complete dialog. A copy of the dialog box statistics is also written to the log file (Help>Display log).
Hmh.. Okay.

So when I try to save the video:
> I do Force Recode
> I change the resolution to 480p
> I set my Bitrates
Yet down in the Audio section, I must select: Automatic, MPEG Layer 2, LPCM/WAV or AAC
You say that VideoReDo doesn't touch the audio settings unless I ask it to. Which option is the one where VideoReDo doesn't recode the audio?

I've tried Automatic (which causes the glitches), and I've also tried AAC (which also causes the glitches at the same time ranges). So how can I set up the save dialog to not touch the original audio? Thanks.

Okay. I just tried using the MPEG Layer 2 audio settings, yet with this option, I get a different high pitched ringing sound for that time range. The only other one I still didn't try is the WAV audio setting. Yet I know that WAV files are usually very big in size, which would make the output file size to be pretty big.

Sooo... my only known solution for the time being, is to re-encode the video & audio using HandBrake, and then using VideoReDo to trim the video to the precise start & end frames (because HandBrake doesn't do a good job in trimming videos to the exact frames). (One of the reasons why I switched from HandBrake to VideoReDo is because VideoReDo is very precise about trimming videos to exact frames). I'm still sticking with VideoReDo, yet it would be really nice to have this small bug fixed in the audio output settings.
Okay. So I just tried recoding different video, and the same exact thing happens! It also happens at the same time frames!! This never used to happen before! What happened? Why is this happening?


Senior Developer
Staff member
Is the audio changing at that point? Going from 2ch to 6ch, changing sample rate, etc...? With MP4 a single audio header is stored in the MP4 file itself and then the audio headers are stripped from each individual frame. The header from the MP4 is then applied to every frame during playback. Which means that if the audio changes mid-stream the header will be incorrect and it will cause distortion. There is no way for us to check this during output so we just passthrough the audio and assume it's all the same. If the audio does change then you'll need to force a recode of the audio, including setting specific channel and sample rate values, so that it's corrected to all match before it hits the MP4 muxer.
Hi Dan203, thanks for the response. What's strange is that I tried trimming off the beginning and ending parts of a completely different mp4 file, and the same exact thing happened. From minute 6:00 to about 20:00, the audio completely disappeared but re-appeared in-sync after that 20:00 minute mark. Those two mp4 files are completely different and are not related to each other. But what's strange, as well, is that I tried using a different audio setting (I tried MPEG Layer 2 instead of AAC), and the same exact thing happened. So this could imply that there is some setting that got screwed up inside VideoReDo whenever re-encoding the audio part of a video file.

Also I have a question. Can you please tell me how to pass-through the audio of a video file? From the attached picture above, I click on the drop-down list of Audio Encoding type, yet there is no audio pass-through. How can I do that please?


Senior Developer
Staff member
"Automatic" is passthrough IF the output container supports the audio format of the source stream. In most cases that's always passthrough, but there are a few formats where the container doesn't support a specific audio format. If that's the case then you'll see the "Audio recode required" warning in the save dialog.

As for the audio cutting out at 2:00 I have no idea what would cause that. We've never seen any other reports of that behavior. Based on your other post it sounds like there is some change in the audio at that point that's messing up the decoder. If you open the original file and let it play inside VRD until it gets to that point (don't seek, start from the beginning) does it have the same high pitch sound? Or does it go blank?
Okay cool thanks for clarifying how the passthrough works.

And I just tried playing the whole video in the program without pausing/seeking/etc. It played completely normal.

I'll try to reinstall the program and see if this gets fixed.


Senior Developer
Staff member
If it plays OK in the UI then it's not the decoder. Weird that the output file would suddenly have a high pitch squeal at that point but the playback inside VRD was OK. They use the same decoder and channel remapper so I'm not sure why the output would be affected but not the UI. Let me know if the reinstall helps at all. Also try disabling your AV program just to make sure it's not interfering with the output.