[FFmpeg-user] Why do these blank spots appear in spectrograms of converted youtube videos?

[Paul B Mahol]

On 1/6/17, Ethan Lewis <dummycommandline at gmail.com> wrote:
> Hello
>
> I was converting a bunch of youtube videos into 16kHz wav files using ffmpeg
>
> I used the following commands
>
> youtube-dl -f best /path/to/youtube/video/ -f 'bestvideo,bestaudio' -o
> '%(title)s.f%(format_id)s.%(ext)s'
>
> ffmpeg -i /path/to/download/m4a/audio -acodec pcm_s16le -ar 16000 -ac
> test1.wav
>
> When I use these youtube videos
>
> https://www.youtube.com/watch?v=E1mGPeLqg2g
> https://www.youtube.com/watch?v=XBFOP_pF7PY
>
> I see many blank spots in their spectrograms  (see the ones uploaded here
> https://drive.google.com/file/d/0BzNdoGke8tyRSGgwUUtSTkgxdEE/view?usp=sharing
> )
>
> Natural speech should not have such artefacts.
>
> I am confused why this is happening. Is it because of ffmpeg conversion of
> m4a audio OR was it somehow fault of the original recording?

Have you compared with original audio? prior to resampling with ffmpeg?