[FFmpeg-user] live stream - get data from multimedia filter continuously

[Gyan]

On 12-05-2019 10:43 PM, Thomas Seilund wrote:
> Hi All
>
> I capture video stream from webcam and show video on screen.
>
> The same stream goes through the 'metadata' multimedia filter as shown 
> below:
>
> ffmpeg -y -f v4l2 -input_format mjpeg -s hd480 -r 30 -i /dev/video2 
> -filter_complex 
> "[0:0]select='gte(scene,0)',metadata=print:file='movement.txt',null[X]" 
> -map '[X]' -pix_fmt yuv420p -f xv Title
>
> The text file 'movement.txt' gets information about each frame. BUT 
> data is written to text file 'movement.txt' buffered. Is there any way 
> to write data to text file 'movement.txt' as each frame is processed?

Not at present. The file protocol will buffer up to 256 kB and then 
write out. There is an option to write immediately but it isn't applied 
to the metadata filter as its I/O context is isolated. I plan to patch 
that soon-ish.

Gyan