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• How to stream cv2.VideoWriter frames to and RTSP server

  10 juin 2022, par chasez0r

  Environment : Docker, Ubuntu 20.04, OpenCV 3.5.4, FFmpeg 4.2.4

  


  Im currently reading the output of a cv2.VideoCapture session using the CV_FFMPEG backend and successfully writing that back out in real time to a file using cv2.VideoWriter. The reason I am doing this is to drawing bounding boxes on the input and saving it to a new output.

  


  The problem is I am doing this in a headless environment (Docker container). And I’d like to view what's being written to cv2.VideoWriter in realtime.

  


  I know there are ways to pass my display through using XQuartz for example so I could use cv2.imshow. But what I really want to do is write those frames to an RTSP Server. So not only my host can "watch" but also other hosts could watch too.

  


  After the video is released I can easily stream the video to my RTSP Server using this command.

  


  ffmpeg -re -stream_loop -1 -i output.mp4 -c copy -f rtsp rtsp://rtsp_server_host:8554/stream

  


  Is there anyway to pipe the frames as they come in to the above command ? Can cv2.VideoWriter itself write frames to an RTSP Server ?

  


  Any ideas would be much appreciated ! Thank you.

  


• Absolute timestamp as MP4 start time

  14 juin 2016, par galbarm

  I’d like to store the exact start time a video was recorded on, inside its mp4 container.
  I need a millisecond accuracy (i.e. year,month,day,hour,sec,milli).
  Such an accuracy requires 8 bytes.

  The only standard way I found to store a video creation time is to use the mvhd/tkhd/mdhd boxes creation_time field.
  But according to the base media file format spec, the field only gives a granularity of seconds :

  creation_time is an integer that declares the creation time of this
  track (in seconds since midnight, Jan. 1, 1904, in UTC time)

  In version 0 the field size was 4 bytes, while in version 1 it was increased to 8 bytes. But the description remained unchanged so it can still only reflect a timestamp in up to second granularity. (for maintaining backward compatibility maybe ?)

  So finally, is there a standard way to store a single absolute timestamp with millisecond accuracy in a mp4 container ?
  If the only way to do it, is to store it as a custom metadata, is there an agreed common way to do it according to ?

• Text backdrop by ass formatting

  14 septembre 2024, par Armen Sanoyan

  I want to add box behind a word using ass subtitles formatting. The box should have border radius. the ass file later will be used by ffmpeg.

  


  I have tried the BorderStyle=3 form stack ansers 1, 2 both of them do not provide a way to get rounded boxes. Also the BorderStyle=4 didn't work for me. In comments of last stack answer I found a possible reason that my libraries can be old, but anyway it doesn't seem that BorderStyle=4 will solve my problem of border radius. There is another way to achieve rounded box link to answer. I didn't figure it out how to install all the libs he explained there. Also the later answer seems to me over complicated. Is there an other way to make the borders of box rounded without suffering and pain ? I also tried drawing the box with Drawing commands like

  


  {\p1}m 0 0 s 100 0 100 100 0 100 c{\p0}


  


  But it still doesn't seem to be the best way to achieve rounded borders.