[FFmpeg-user] Black screen when capturing Windows desktop with audio (gdigrab, dshow)

[Roger Pack]

On Sun, Jan 22, 2023 at 12:26 PM German Geraskin
<german.geraskin at gmail.com> wrote:
>
> # Disclaimer
> Probably, this message should have been sent as a bug report, but
> unfortunately I was not able to post it on trac.ffmpeg.org since there is
> no tool to recover forgotten username on that site.
>
>
> # Versions
> The issue that will be discussed below was observed on the following
> software.
> Operating system: Windows 10 Pro (version: 21H2; build: 19044.2130)
> FFmpeg: 4.x.x and 5.x.x versions
>
>
> # Short Description
> "Black screen" appears when I try to capture desktop and record audio with
> respective input devices, gdigrab and dshow.
>
>
> # Detailed Description
> The command to capture Windows desktop without sound recording works
> flawlessly.
>
>   ffmpeg.exe -f gdigrab -framerate 25 -offset_x 54 -offset_y 114
> -video_size 960x540 -show_region 1 -i desktop -pix_fmt yuv420p -r 25 -g 50
> -c:v libx264 -preset veryfast -profile:v high -crf 28 -f mp4 -y
> gdigrab-without-audio.mp4
>
> Please check the video file produced by this command:
> https://0x0.st/ohDQ.mp4/gdigrab-without-audio.mp4
>
> The command to capture Windows desktop AND record audio at the same time
> does not work as expected. FFmpeg starts working normally, but when the
> user (surprise) clicks the MOUSE button, Windows starts showing a black
> rectangle in the capture region and FFmpeg captures it.
>
>   ffmpeg.exe -f gdigrab -framerate 25 -offset_x 54 -offset_y 114
> -video_size 960x540 -show_region 1 -i desktop -f dshow -i audio="Microphone
> (Logitech USB Headset H540)" -pix_fmt yuv420p -r 25 -g 50 -c:v libx264
> -preset veryfast -profile:v high -crf 28 -c:a aac -b:a 64k -f mp4 -y
> gdigrab-dshow-audio-ISSUE.mp4
>
> Please check the video file produced by this command:
> https://0x0.st/ohDj.mp4/gdigrab-dshow-audio-ISSUE.mp4
> (Sound ON)
>
> I believe that this behavior is common to all versions of FFmpeg.
> Here are list of four builds tested with the same result:
> * ffmpeg-n5.0-latest-win64-gpl-5.0
> * ffmpeg-n4.4-latest-win64-gpl-4.4
> * ffmpeg-4.1-win64-static
>
>
> # Solution
> After some research, I guessed that this phenomenon occurs when some
> message, that FFmpeg cannot correctly interpret, arrives on FFmpeg standard
> input when the mouse button is clicked.
>
> To test this my hunch, I tried to start FFmpeg in a new detached console.
> And it worked!
>
>   start ffmpeg.exe -f gdigrab -framerate 25 -offset_x 54 -offset_y 114
> -video_size 960x540 -show_region 1 -i desktop -f dshow -i audio="Microphone
> (Logitech USB Headset H540)" -pix_fmt yuv420p -r 25 -g 50 -c:v libx264
> -preset veryfast -profile:v high -crf 28 -c:a aac -b:a 64k -f mp4 -y
> gdigrab-dshow-SOLVED.mp4
>
>
> # Conclusion
> Apparently, the issue described above is a bug of the Windows operating
> system itself, but not the FFmpeg.
>
> In conclusion, I would like to note that in this experiment, both the mouse
> and the microphone were connected via USB.
> Perhaps this is important for reproducing the issue and working on fixing
> it.

Do you click in the console to create the problem?