how to create a .wav file empty correspondant to a video-only file?

[marcorocchini]

Hi cats,

I have a example.mp4 that have the video track but no audio.
Simply I need to generate with ffmpeg a example.wav mute audio track that have the same lenght of the example.mp4

is it pobbile? thanks

[TreeTops]

Did you try Audacity?

[cholla]

This works for me.
I had to remove the audio track from the .mp4 first.
I'm not sure how top do it with a .wav but this works with aac:
ffmpeg -f lavfi -i aevalsrc=0 -i input.mp4 -c:v copy -c:a aac -map 0 -map 1:v -shortest output.mp4

[zing269]

use -c:a pcm_s16le for .wav

[cholla]

use -c:a pcm_s16le for .wav

That is fine for .mkv & some other formats but not for the .MP4 format.

[Cornucopia]

use -c:a pcm_s16le for .wav

That is fine for .mkv & some other formats but not for the .MP4 format.

That's because LPCM is not normally a supported stream type in mp4. I wouldn't expect it to work, for you or for the OP.

Scott

[cholla]

That's why I gave the command line for aac audio.

AFAIK ffmpeg would convert a .wav audio track to .aac or .mp3 automatically by removing-c:a copy .

Like this:

ffmpeg -i input.wav -c:v copy output.mp4

This creates an AAC (LC) audio track in a .mp4 container.

[zing269]

ffmpeg -f lavfi -i anullsrc -t 300 -c:a pcm_s16le out.wav

will create a 5 minute long .wav @ 44,100 Hz, 16 bit, stereo.

Adjust the -t parameter to the needed length in seconds and replace pcm_s16le with the required type of sample format. See https://trac.ffmpeg.org/wiki/audio%20types for a list.

[marcorocchini]

maybe I have do a mess but in some way I think to have get the target, but exactly I don't know why. This is the subroutine

IF NOT "%OnlyOneTrackMonoStereo%"=="1" IF NOT "%multipleAudioStreamDetected%"=="1" IF NOT EXIST "%cd%\decisor.mov" If NOT "%isMXF%"=="1" ffmpeg64bitAug2019.exe -loglevel quiet -y -threads auto -y -f concat -safe 0 -i concatList.txt -map 0:? -vcodec copy -acodec copy "%cd%\decisor.mov"
IF NOT "%OnlyOneTrackMonoStereo%"=="1" IF NOT "%multipleAudioStreamDetected%"=="1" if NOT "%isMXF%"=="1" fart.exe "%cd%\decisor.avs" "###spaceForSource##" "%cd%\decisor.mov"
IF NOT "%OnlyOneTrackMonoStereo%"=="1" IF NOT "%multipleAudioStreamDetected%"=="1" if NOT "%isMXF%"=="1" ffmpeg64bit2014.exe -y -loglevel quiet -threads auto -i "%cd%\decisor.avs" -acodec copy "%cd%\decisor.wav"
IF NOT "%OnlyOneTrackMonoStereo%"=="1" IF NOT "%multipleAudioStreamDetected%"=="1" if NOT "%isMXF%"=="1" IF EXIST "%cd%\AllWav\canaleAudio1_2.wav" del "%cd%\AllWav\canaleAudio1_2.wav"
IF NOT "%OnlyOneTrackMonoStereo%"=="1" IF NOT "%multipleAudioStreamDetected%"=="1" if NOT "%isMXF%"=="1" if NOT "%isMXF%"=="1" copy /y "%cd%\decisor.wav" "%cd%\AllWav\canaleAudio1_2.wav"
IF NOT "%OnlyOneTrackMonoStereo%"=="1" IF NOT "%multipleAudioStreamDetected%"=="1" if NOT "%isMXF%"=="1" ffmpeg64bit2014.exe -y -threads auto -i "%cd%\decisor3OR4.avs" -acodec copy "%cd%\AllWav\canaleAudio3_4.wav"


       rem #### check duration of avigen file ####
        if exist aviGenDuration.txt del aviGenDuration.txt
        Set "aviGenDuration=undef"
        FFProbe64bit2014.exe -loglevel fatal -show_entries format=duration -of csv="p=0" -sexagesimal "%cd%\decisor.mov">aviGenDuration.txt   
        set /p aviGenDuration=<aviGenDuration.txt
        if exist aviGenDuration.txt del aviGenDuration.txt
        echo durata pari a %aviGenDuration%


IF "%testEsistenzaAudio%"=="0" ffmpeg34_64bit.exe -y -f lavfi -i aevalsrc=0 -i "%cd%\decisor.mov" -af "pan=stereo:c0=c0:c1=c1" -c:a pcm_s16le -ar 48000 -shortest -t %aviGenDuration% decisor.wav
IF NOT "%OnlyOneTrackMonoStereo%"=="1" if NOT "%isMXF%"=="1" IF NOT "%multipleAudioStreamDetected%"=="1" v:\automazioneclip\core\ffmpeg34_64bit.exe -loglevel quiet -y -threads auto -i "%cd%\decisor.mov" -i "%cd%\decisor.wav" -i "%cd%\decisor.wav" -map 0:v:0 -map 1:a:0 -vcodec copy -c:a pcm_s16le -ar 48000 "%cd%\decisorRemuxed.mov"

IF NOT "%OnlyOneTrackMonoStereo%"=="1" If NOT "%isMXF%"=="1" IF NOT "%multipleAudioStreamDetected%"=="1" IF NOT "%testEsistenzaAudio%"=="0" ren "%cd%\decisorRemuxed.mov" "concatHD.mov" & echo "%cd%\allwav\usataRoutineDecisorCon%numeroCanaliAudio%canaliAudio">"%cd%\allwav\usataRoutineDecisorCon%numeroCanaliAudio%canaliAudio.txt"

IF NOT "%OnlyOneTrackMonoStereo%"=="1" If NOT "%isMXF%"=="1" IF NOT "%multipleAudioStreamDetected%"=="1" IF "%testEsistenzaAudio%"=="0" ren "%cd%\decisorRemuxed.mov" "concatHD.mov" & echo "%cd%\allwav\usataRoutineDecisorCon%numeroCanaliAudio%canaliAudio">"%cd%\allwav\AudioAssenteInOrigineVieneGeneratoAudioMuto.txt"

IF NOT "%OnlyOneTrackMonoStereo%"=="1" If NOT "%isMXF%"=="1" IF NOT "%multipleAudioStreamDetected%"=="1" IF "%testEsistenzaAudio%"=="0" copy /y "%cd%\decisor.wav" "%cd%\AllWav\canaleAudio1_2.wav"

maybe the correct way is to generate a intermediate .mov with only the video, and test the duration. And then create an empty .wav of the same duration. The wav achieved is ready to be remuxed in a new file with video and audio (but audio in silence, with 2 audio channels)

[cholla]

maybe I have do a mess but in some way I think to have get the target, but exactly I don't know why. This is the subroutine

maybe the correct way is to generate a intermediate .mov with only the video, and test the duration. And then create an empty .wav of the same duration. The wav achieved is ready to be remuxed in a new file with video and audio (but audio in silence, with 2 audio channels)

Yes a mess.
I believe you will end up with a .MOV file.
Is this correct?

Did you try this as it worked for me:

ffmpeg -f lavfi -i aevalsrc=0 -i input.mp4 -c:v copy -c:a aac -map 0 -map 1:v -shortest output.mp4

This will create a video with a silent aac (lc) audio track of the same length as the video.

A valid audio MP4 must contain an MPEG audio track (mp3 or aac).
This means you can not have a .WAV audio track in a .MP4 container.
Or a PCM audio track.

[ProWo]

Hi cats,
I have a example.mp4 that have the video track but no audio.
Simply I need to generate with ffmpeg a example.wav mute audio track that have the same lenght of the example.mp4
is it pobbile? thanks

What is the purpose of a silent stereo audio track?

[cholla]

Hi cats,
I have a example.mp4 that have the video track but no audio.
Simply I need to generate with ffmpeg a example.wav mute audio track that have the same lenght of the example.mp4
is it pobbile? thanks

What is the purpose of a silent stereo audio track?

I wondered the same thing.
There must be a reason.

[marcorocchini]

Did you try this as it worked for me:

ffmpeg -f lavfi -i aevalsrc=0 -i input.mp4 -c:v copy -c:a aac -map 0 -map 1:v -shortest output.mp4

[Attachment 65959 - Click to enlarge]

mmm it maybe good, but I don't know exactly if it works also for conCat input (ffmpeg.exe -loglevel quiet -y -threads auto -y -f concat -safe 0 -i concatList.txt ...)

[cholla]

What is the purpose of using concat ?

Also why is the silent audio track needed?

[Cornucopia]

He will probably give the "excuse" that he's a "cat", as if that solves anything.


Scott

[marcorocchini]

What is the purpose of using concat ?

Also why is the silent audio track needed?

because I need to concatenate all the .mp4 of the drone dji footage, and I need to put all in avisynth. But avisynth parse all with a necessary audio track (also if mute). Dji osmo for example does have audio inside each .mp4 but the drone does not have any audio track

[cholla]

First is the acc in the ffmpeg code I posted acceptable for the silent audio track ?

What is the codec of the audio tracks in the Dji Osmo .MP4s ?

Someone else is going to need to help with this.
I haven't used avisynth by itself only as part of other software.
I'm not good at creating batch files.
I have only used concat with a few DVDs.

I take it you are trying to put several drone videos together into one?

[marcorocchini]

osmo seems to me have aac audio. Drone dji don't have any audio track

[Cornucopia]

Concatenation only works reliably when all elements have the same stream configuration. So either drop the audio of the osmo files prior to concat, and then do a video stream only concat, or do what cholla said and add an aac tracks to the drone files - prior to the concat - and then concat with video and audio streams.
Or, do separate concats for video-only streams vs v+a streams.

Avisynth scripts can be designed to work with audio, or ignore audio. If must have audio, avisynth can also generate a silent track for use with silent clips in combination along with tracks WITH audio.
But you must be consistent, as neither AVISynth nor ffmpeg, nor most other editing/processing apps I can think of will be happy with a checkerboard of audio-noaudio-audio-noaudio.

My recommendation to you is that you use fprobe to assist with script-based ffmpeg generation of an aac track for video-only clips, then remux, then when they are all consistent do the concat.


Scott

[cholla]

This was the original post & what was asked for:

Simply I need to generate with ffmpeg a example.wav mute audio track that have the same lenght of the example.mp4
is it pobbile? thanks

Since the .MP4 contaier can't have a .wav or PCM audio track I used aac.
The code I posted produces a silent audio track the same length as the video track.

It was afterwards all the concat or other joining came up.

If I was doing this I would join all the videos with silent & sound audio track with MKVToolNix.
Into one .mkv . Problem solved.

I might even try ProWo's Cleaver but I have only used it a little bit.
So I can't say that it would work for sure.
It would use FFMPEG though.