I downloaded some simple 2 channel stereo video files in MKV format. I can play the files in VLC player to confirm the audio is present.
I follow the exact same steps as shown in the youtube video (https://www.youtube.com/watch?v=C1XO3cgwHIg).
The resulting video file has no audio.
I noticed in the youtube instruction video he unchecked the audio stream. I tried that the first time, no audio. On the second attempt I return the check mark to the audio stream. The audio details show Output AAC 2.0, quality 0.75.
After processing the file, the icon on the audio track is replaced by the red circle with the white "X". And as my title suggests, there is no audio.
Viewing the MkvToMp4 log window, the first test had no comments about the audio track, and I see the following text referring to the audio in the 2nd test.
...file name YouTube_internal_audio_2_new.opus" +65529ms -progressnumbers
WAV, 2.0 channels, 0:03:43, 16 bits, 1536kbps, 48kHz
Eac3To terminated with error: 1
I have tried several different MKV to MP4 converters that are recommended on the Videohelp website, and each of them generates an mp4 file with no sound.
The only tool that retains the audio track is VLC Player, but it took the VLC player 9 minutes to convert the 3:43 video to mp4.
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I tested another MKV with Opus audio. Box4 reported no problems, the resulting mp4 file has no audio when opened in VLC, and does not play at all when opened in Media Player.
Should I try a different tool to save the MKV files from YouTube?
(Currently using Video DownloadHelper add-on for Firefox 54.0.1)
I'm not really familiar with DownloadHelper. Youtube does provide AAC audio. Personally, I use youtube-dl from the command prompt. It can download/create H.264 + AAC in MP4 automatically.
youtube-dl -f "bestvideo[ext=mp4]+bestaudio[ext=m4a]" "URL"
OK. So I downloaded youtube-dl.exe
I run the program one time to make sure it does not need to extract or unzip anything.
I drop a copy of the exe file into my system path in the C:\Windows\system32 folder as instructed on the youtube-dl page of this website.
I open a command prompt, enter the text exactly as you desribed and the app crashes with a Fatal Python Error.
Starting to wonder if I am jinxed.
Don't put it in system32 folder. Try somewhere else.
Or you could try this converter: http://www.pazera-software.com/products/mkv-to-mp4-converter/
If all else fails Pazera makes an free audio converter which can handle Opus
Convert it and mux the separated audio conversion with the video file.