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

Thomas Seilund tps at netmaster.dk
Sun May 12 22:06:10 EEST 2019

On 12/05/2019 19.25, Gyan wrote:
> 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
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Thanks Gyan.

Is there another way to get the metadata, ie. lavfi.scene_score, as the 
frame is processed?

Basically, I want to take some action when there is motion in the video!

Thanks Thomas S

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