Sur d’autres sites (1560)

• GoPro (MP4) video timestamp sync with precision of milliseconds

  3 février 2021, par Raphael Ottoni

  I need your help with a data sync problem... I m currently trying to sync my GoPro video with real world time (a.k.a my notebook). I manage to sync date and time of my notebook and my GoPro 3+ black perfectly. The problem is that when the GoPro save the files in disk it round up the milliseconds on the creation_time (the milliseconds is always 000000) . Thus, turning the perfect sync impossible. In attachment is a picture of the meta information (extracted by ffprobe) of the MP4 video.

  



  My question is : What I have to do, so the GoPro actually save the creation_time with precision of milliseconds ?

  



  Another small question : Looking at the attachment figure, we see the "timecode" which is a time synchronization data in the format of hours:minuts:seconds:frame. I was thinking that I could use the "frame" value to calculate the missing milliseconds value. If we take this attachment, as a example, we can see that the frame value is "36". Meaning that the millisecond that it started to record was the one associated with the 36th frame of the FPS (in this video : 60fps) value : Some thing like 1000/60 * 36 which is 600 milliseconds, thus the actual creation_time of this video would be : 2017-07-19T18:10:34.600

  



  Is this logic right ? it didn't work ! I don't know what else to do.

  



  P.S : I need this kind of time precision because I will sync the video frames with a external sensor data that is recorded at 11hz.

  



  Please Help

  



  

  



  update

  



  I forgot to mention, even if you check the original raw file information, inside the GoPro SSD card, using "stats" to read the creation time (see attachment) it still has the same timestamp without milliseconds.

  



  

  


• FFMPEG : embed current time in milliseconds into video

  22 décembre 2023, par stevendesu

  I would like to embed the computer's local time in milliseconds into a stream using FFMPEG.

  



  I can embed the local time in seconds using drawtext like so :

  



  ffmpeg -i <input /> -vf "drawtext=text=&#x27;%{localtime\:%T}&#x27;" -f flv <output>&#xA;</output>

  



  Looking through the documentation for drawtext, doing some tests, and Googling around, it seems like localtime and gmtime don't provide milliseconds — just seconds. However the pts options does have milliseconds :

  



  ffmpeg -i <input /> -vf "drawtext=text=&#x27;%{pts\:hms}&#x27;" -f flv <output>&#xA;</output>

  



  I also found out that pts supports an offset, so I was able to use something like this to display local time (kind of) :

  



  ffmpeg -i <input /> -vf "drawtext=text=&#x27;%{pts\:hms\:$(date &#x2B;%s.%N)}&#x27;" -f flv <output>&#xA;</output>

  



  This had two problems :

  



  

  1. It displayed something like 17499:17:29 for the time... I found a (rather complex) way to work around this

  


  2. It uses the server's current time when you first run the ffmpeg command as the offset — not the server's current time when ffmpeg actually starts decoding video. I noticed ffmpeg had about a 2-second startup time, causing the clock to be off by roughly 2 seconds

  


  



  Is there a way to modify my solution, or an entirely separate solution, that can embed server local time in milliseconds into the stream ?

  


• extract frames using ffmpeg and find out their offset (milliseconds)

  24 février 2019, par ori silberberg

  I wish to extract 10 consecutive frames every 2 seconds.
  (this is because I wish to choose "best one" from the "nearby offset").
  I know how to extract a frame each x seconds :

  ffmpeg -i /tmp/V.MP4 -vf fps=1 %02d.jpg

  I know how to extract 10 frames from some starting offset :

  ffmpeg -ss 20.0 -i /tmp/V.MP4 -vframes 10 %02d.jpg

  I have 2 issues :

  1. How do I find the offset for each output image ? I can try and calculate it (using the video fps, which is 29.97 in my case) but it sounds like a bad idea - the data is right there in the video for ffmpeg to grab..
  2. Is there an efficient way to "merge" the two commands into one, therefore getting 10 consecutive frames each x seconds ?