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• How can I tell ffmpeg to start to write on file as soon as it detects some motion ?

  29 mai 2017, par krvl

  A little background. I am recording a stream from a camera (using rtsp protocol) and I’d like to save on the disk not the whole input stream but only some excerpts after a motion is detected.
  The "basic" command I’m using is something like :

  ffmpeg -i rtsp://{my_camera_address}/ -movflags +frag_keyframe+separate_moof+omit_tfhd_offset+empty_moov -acodec aac -vcodec h264 output.mp4

  I recently add the -movflags option to achieve a sort of realtime, that is I can read the video file while is’t been written by ffmpeg.
  A user suggested in this question to add a filter to ffmpeg command in order to grab only the frames where a motion is detected, they used this option :

  -vf select=gt(scene\,0.05),setpts=N/(25*TB)

  But it has some incompatibility with the -vcodec copy option, although this is not a big issue.

  My question is : is it possibile to use the filter (or another option) just to trigger the file writing ? For example, I save a 5 minutes video after a motion-detection is triggered.

• Scenecut detection and consistent GOP size - adaptive streaming

  24 mars 2014, par Tarun

  Sample Command :

  -map 0:0 -f mp4 -vcodec libx264 -preset slow -profile:v main -vf scale="640:trunc(ow/a/2)*2" -vb 700k -minrate 650k -maxrate 750k -bufsize 10000k -an -g 48 -x264opts keyint=48:min-keyint=10:scenecut=40 -flags +cgop -sc_threshold 40 -pix_fmt yuv420p -threads 0 -y

  There is as such no error in encoding, But I wanted to understand following points-

  1) the above command will ensure that range of GOP size is 10,48, and if any scene change value (frame1 to fame2) is >40%, then a keyframe is introduced there ?

  2) So that means in a 3 hours of source video, there is no guarantee that GOP size will remain same

  3) No consider, I am creating 7 MP4 files each with different bitrate and resolution. (These Mp4s will be encoded to smooth in later stage). Hence i am targeting adaptive streaming. But when I did that, I found that if GOP sizes were not consistent across each bitrates. What I mean by this is, for ex : if in Bitrate1 - GOP size is like 10, 20, 48 and so on, in other bitrates it wasnt in the same sequence. I hope my question makes sense.

  So is there a way to ensure that GOP size may vary across one single output. But it should be consistent across each bitrate provided that the source is same ?

  Also for adaptive streaming Is scenecut detection advisable ?

• Add Timestamp to extracted thumbnail's name from a video file

  12 décembre 2013, par Harish Varada

  I have a requirement of generating thumbnails(camera change, slide change, scene change) from a videofile with it's timestamp(pos) included in the generated output thumbnails.

  I used the following command to generate thumbnails :

  ffmpeg -i input.mp4 -vf select="eq(pict_type\,I)" -vsync 0 -an keyframe-%06d.png

  This command works absolutely fine for generating thumbnails (assume 15 thumbnails are generated) with names in sequence like : keyframe-000001.png, keyframe-000002.png, .... , keyframe-000015.png.

  But, according to my requirement, I need the output thumbnail file names something like as follows :

  keyframe-001426.png, keyframe-002769.png, .... , keyframe-014571.png where

  001426 is the position of thumbnail keyframe-000001.png

  002769 is the position of thumbnail keyframe-000002.png

  014571 is the position of thumbnail keyframe-000015.png

  Is there a way to achieve this in a single command.? Please help me out achieving this.