Use handbrake to convert audio to stereo without re-encoding video

[paqman]

Hey everyone, I made a mistake, and captured a bunch of Hi8 tapes using only one channel for audio. The camcorder only has one audio input, and I didn't think to use a Y-adapter. When converting the video in handbrake, the audio mixdown was set to stereo, so I falsely assumed that it would convert the mono channel to come out both right and left. So now I have about a dozen videos going out the right channel only. If I have to re-capture all these videos I can, just trying to avoid that. I can process the videos through Handbrake again and choose the "mono" option, which I believe should mixdown the mono audio to go out both channels right? (If that's wrong, please let me know what audio setting I should use)

But my main question is, is there a way to re-run the videos through handbrake with the new audio option, without re-encoding the video? I feel like re-encoding, even with the same presets is going to lower the original video quality. I'd prefer to not mess with the video and leave it lossless from what I already have converted. Thanks!

[ron spencer]

handbrake does not have a pass-thru option, so no. myFFMPEG does...as do other FFMPEG-based tools.

[TeeDawwg]

Avidemux allows you to COPY the video while re-encoding the audio only. I have used this to quickly change audio codecs. Looks like you can VIDEO Output to Copy and then change the audio to a codec that works for you, click the FILTER button and window opens where you can remix to stereo. Audio only reencodes are fast....I have played with these to find a combo that works with my media server and Roku media players.

[paqman]

Thanks guys that's perfect. I just tested one with myFFMPEG. Selected video passthrough, and changed the audio channels to mono and that did the trick! Thanks a bunch. If I have to do it more, I may look at Avidemux as well because the myFFMPEG is just a trial. But thanks again, that worked great. Saved me having to re-capture 15 tapes lol. I'm capturing them now with a y-splitter so I shouldn't have a problem with the rest. (There are over 100 of them lol)

Edit: I do find it interesting that the resulting file is a bit smaller than the original. I would have figured since it's mixing the mono channel out to 2 channels that it would have increased a bit in size.

[paqman]

Ha well maybe I spoke too soon. myFFMPEG worked great, but didn't realize the free trial was for only 5 conversions. With my trial and error, I only got 2 conversions out of it. Anyway, I only have these 15 videos to convert and I've already spent so much money on this project (capturing home movies for my parents), trying to be cheap her. So I tried Avidemux. However, no matter how I configure the Audio, it keeps coming out as mono, only coming out of the left channel. What am I doing wrong? I've tried setting Remix to stereo and mono, and neither one gets the audio coming out of both channels. If I absolutely must I can buy myFFMPEG, but man I'm tired of spending money on this lol.

Also Avidemux seems to double the size of the file, even though I just have "copy" set for Video output. What's up with that?

[davexnet]

Can you provide a 15 second sample cut from the source video?
You can use Mediainfo to get the video/audio details

Mediainfo should confirm

Channel(s)                               : 1 channel

In which case the system should play it across both speakers. If it does not, something is wrong with
your PC sound settings

[alex]

Another totally free program to try which may work is clever FFmpeg available on this site.

[alex]

This one is simpler to use. Clever FFmpeg GUI

[ProWo]

You can do this very easily with clever FFmpeg-GUI.
Follow the instructions carefully the first time you start it.

Then load your video, click main, click convert audio stream, click continue, set channels to 1(mono), leave everything else as it is, click convert.

[Attachment 61662 - Click to enlarge]
Click multiplex, the newly created audio mono stream is green, deselect the old audio stream and click multiplex.

[Attachment 61663 - Click to enlarge]
Done.

[jagabo]

Here's an ffmpeg command line for a batch file:

ffmpeg -i %1 -map_channel 0.1.0 -c:v copy -c:a mp3 -b:a 128k "%~dpn1.mono.mkv"

Put it in a batch file called LeftToMono.bat or RightToMono.bat and you can drag/drop files onto the batch file to convert them. New new file will have ".mono" added to the end of the filename. "filename.mvk" will become "filename.mono.mkv". Put the batch file in your SendTo folder and you can right click on any A/V file and select SendTo -> LeftToMono.bat (or RigthToMono.bat, or whatever name you give it). You can easily put the command in a For loop to process all files in a folder, all files in a folder tree, or even all files on a drive.

Change "-map_channel 0.1.0" to "-map_channel 0.1.1" to keep the right channel rather than the left channel. The meaning of the three numbers is file#.stream#.channel#. Since we're working with a single input file the first value will always be zero. If your audio stream isn't stream #1 you'll have to change the second number. Most files have the video as stream 0, the first audio stream as stream 1. But you will sometimes see them in a different order.

Change the audio codec from mp3 to another if you want (aac, ac3, etc.) Change the audio bitrate as desired.

Change the container from mkv to whatever you want (mp4, mov, mts, etc.) and whatever is compatible with the video and audio streams (for example, you can't put uncompressed pcm, "-acodec pcm_s16le, in mp4, so use mov instead).

[paqman]

You can do this very easily with clever FFmpeg-GUI.
Follow the instructions carefully the first time you start it.

Then load your video, click main, click convert audio stream, click continue, set channels to 1(mono), leave everything else as it is, click convert.

[Attachment 61662 - Click to enlarge]
Click multiplex, the newly created audio mono stream is green, deselect the old audio stream and click multiplex.

[Attachment 61663 - Click to enlarge]
Done.

Thanks! This worked really well.

Here's an ffmpeg command line for a batch file:

Code:

ffmpeg -i %1 -map_channel 0.1.0 -c:v copy -c:a mp3 -b:a 128k "%~dpn1.mono.mkv"

Put it in a batch file called LeftToMono.bat or RightToMono.bat and you can drag/drop files onto the batch file to convert them. New new file will have ".mono" added to the end of the filename. "filename.mvk" will become "filename.mono.mkv". Put the batch file in your SendTo folder and you can right click on any A/V file and select SendTo -> LeftToMono.bat (or RigthToMono.bat, or whatever name you give it). You can easily put the command in a For loop to process all files in a folder, all files in a folder tree, or even all files on a drive.

Change "-map_channel 0.1.0" to "-map_channel 0.1.1" to keep the right channel rather than the left channel. The meaning of the three numbers is file#.stream#.channel#. Since we're working with a single input file the first value will always be zero. If your audio stream isn't stream #1 you'll have to change the second number. Most files have the video as stream 0, the first audio stream as stream 1. But you will sometimes see them in a different order.

Change the audio codec from mp3 to another if you want (aac, ac3, etc.) Change the audio bitrate as desired.

Change the container from mkv to whatever you want (mp4, mov, mts, etc.) and whatever is compatible with the video and audio streams (for example, you can't put uncompressed pcm, "-acodec pcm_s16le, in mp4, so use mov instead).

This is really slick thanks. I was trying the CLI, but couldn't quite get the right flags. This works really well because I can run them through a loop with this and do them all at once. Thanks a bunch.

Thanks for all the great help everyone, we got it solved, and cheaply.