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• A 'clean' way to cut an MP4 movie into two sections using FFMPEG ?

  30 août 2020, par Peter in Japan

  I am attempting to use FFMPEG to make a script that can easily split a short MP4 movie with sound into two pieces at a certain point. I've searched through what feels like hundreds of posts to try to find "the" answer, but most of my attempts end up with poor results, broken video files that cause my video play to freeze, and so on. I am attempting to make a script that allows me to easily cut a short anime movie (something grabbed from Twitter or some other short source) and cut it into two sections, so it can be under the 2:20 Twitter time limit, or to cut out some scene I don't want to show my followers.

  


  The issue is that FFMPEG is good at cutting videos into segments, but bad at know where keyframes are, so most videos have two seconds of blank video at the front before some keyframe appears, which looks terrible.

  


  One example I found that works well is below, which cuts any mp4 into a bunch of chunks of n second size (six seconds in the example below). Source and documentation for this is https://moe.vg/3b8eNTs

  


  ffmpeg -i seitokai.mp4 -c:v libx264 -crf 22 -map 0 -segment_time 6 -reset_timestamps 1 -g 30 -sc_threshold 0 -force_key_frames "expr:gte(t,n_forced*1)" -f segment output%03d.mp4

  


  This code works great, at least allowing me to access the "left" side of a video that I want, in this case a six-second segment I want. Can anyone tell me how to accomplish the above, but starting at the 13-second period in said video, so I could get right "right" (not starting from 00:00:00) video cut cleanly ?

  


  Alternately, a single, unified and elegant way to split (re-encode) an MP4 into two segments that forces keyframes from the very beginning of the cut pieces would be wonderful. I can't believe how hard this seems to be.

  


  Thanks in advance for any help you can give ! Greetings from rural Japan !

  


• Capture and Record Desktop Screen with/as Webcam Video

  4 mars 2021, par Bilal Ahmed Yaseen

  Webcam lets others view either still pictures or motion video of a user or other object in front of it. I want to configure Webcam in a way that it start capturing desktop screen instead of what is in front of it.

  



  I want to manipulate desktop screen captured through Webcam using FFMPEG library. Such as :

  



  ffmpeg -f dshow -i video="Integrated Webcam" -f mp4 cam_stream.mp4


  



  I want to use this same application to capture my Desktop Screen that will be possible just in that case when Webcam will be able to capture my Desktop Screen instead. So above command will start recording what Webcam will be capturing that I want it to capture my desktop screen.

  



  Note : I know other ways to capture, record or stream desktop screen but I want to achieve it through Webcam.

  



  What I tried so far : I tried some Fake/Virtual Webcam software (manycam, sparkocam etc.) but I don't think they fulfil what I exactly want.

  



  P.S. I posted the same question in another community but didn't get any response.

  



  Please guide me if there is any way to achieve this ? Thanks

  


• FFmpeg live rtmp capture to segments and encoding to mp4 is causing time glitches in the output

  19 août 2020, par ezwrighter

  I am having issues with capturing live video and converting the latest x minutes to a useable mp4 on demand.

  


  Currently i am capturing the latest 15m of a live rtmp stream and recording it with visual timestamp on it and saving it to segment files like this :

  


  ffmpeg -i rtmps://domain/myawesomestream.stream -map 0 -vf drawtext=x=10:y=10:shadowcolor=white:shadowx=1:shadowy=1:text='%{localtime\:%m/%d/%Y %H\\\:%M\\\:%S MST}' -vcodec libx264 -crf 21 -acodec copy -an -start_at_zero -f segment -segment_time 15 -segment_wrap 61 -segment_list_type ffconcat -segment_list_size 60 -segment_list bufferTime.ffcat -segment_format mpegts /dvr/captureTime-%03d.ts

  


  This works and allows me to always have the latest 15m of video captured with usable segments that I can then roll into mp4 files on demand like this without any re-encoding :

  


  /usr/bin/ffmpeg -safe 0 -f concat -i /dvr/bufferTime.ffcat -c copy -f mp4 /var/www/chat/dvr/ugb/fifteenminutesofvideo.mp4

  


  This does a great job of giving me the last 15 minutes of video from the live stream at any given moment. However, I would like to be able to get the last X minutes of video from the current segments instead of having to get the whole 15m minutes, without more encoding. I can sort of do it with two passes like this :

  


  /usr/bin/ffmpeg -safe 0 -f concat -i /dvr/bufferTime.ffcat -c copy -f mp4 -y /dvr/tmp/mywhole15minutes.mp4
/usr/bin/ffmpeg -sseof -120 -i /dvr/tmp/myshole15minutes.mp4 -c copy -f mp4 -y /dvr/my120secondsofvideo.mp4

  


  This gives me the last 120 seconds of video, but the front of the video has timestamp or keyframe issues at the front of it. It shows the visual timestamp between 5-12 seconds behind and then pauses or jumps the empty frames (Depending on the player) and then starts to play normally. I would love to fix the front of this video and have played with genpts and other flags to no avail :-( Any hints that might push me in the right direction ? Thanks ffmpeg pros out there ! I don't have a great place to publicly host the bad encoded video file, but would be happy to PM a link.