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• Insert keyframe into m4v/mp4 at specific times

  31 janvier 2024, par reynoldsnlp

  I have a program for educators (written with electronjs framework) that plays videos, skipping to preset points in the video as defined in a companion JSON file. Sometimes there is a significant lag after a skip, and this answer suggests that the lag is there because of infrequent keyframes.

  



  Assuming this is correct, I would like to insert keyframes at exact points in the mp4 file where I know the player will skip to. However, some of these video files are already quite large, so I do not want to decrease the keyframe interval, thereby making the files even larger. I only need to force a handful of keyframes in the entire file.

  



  I would like to be able to pass an argument (to ffmpeg, for example) with the times at which I want to force keyframes. Preferably, I would like to do this without re-encoding the entire video (just like this unanswered question), but if I have to reencode the video, I could do that too.

  


• Streaming Encoded MPEG-4 live video from a web camera using RTP in C++

  6 mars 2017, par Maad A.Galil

  I have been working on building a video streamer from a webcam using RTP protocol in C++ language in Linux. I was able to use opencv to take frames from the webcam and send them frame by frame to a client app that shows those frames one by one using the same frame per second parameter.

  But that is mostly a MJPEG kind of transfer as the encoding used is JPEG encoding with a specific quality for each frame. However, I would like to use MPEG-4 encoding before transferring the video. After a deep search online I found out that ffmpeg is the best for such purpose. But the samples online mostly work through a command line interface to capture a webcam video and save it as a video file with the given encoding and format.

  What I am asking about here. Is there a possibility to encode the webcam "LIVE", and get byte data while encoding the camera stream. I would like to use those byte data to transfer it using RTP for example. And then I would like to decode the received byte data and show the video using opencv imshow function for example.

  I hope that I could explain my question clearly.

  Thanks in advanced,

  Yours,
  Maad

• VBR header created for CBR encoded mp3 when using ffmpeg with lame codec ?

  7 novembre 2012, par user784637

  When I run this command to perform a lossy-to-lossy transcode from a youtube video (audio encoded in either aac or vorbis) to mp3 at constant bit rate (cbr)..

  ffmpeg -y -i input.vid -vn -acodec libmp3lame -ab 128K -- output.mp3

  the resulting file has a Xing header (intended to be associated with variable bit rate, vbr, files) instead of CBR header. I do not know if this is an issue with ffmpeg or with the lame codec. How do I force a CBR header to be written instead of the Xing Header ?

  The reason I ask is because on some old software, the song loops perpetually and on older firmware of some mp3 players the song will cause the player to crash due to the header discrepancy.

  If it's not possible to force a CBR header to written, are there any linux command line tools that can change this header ? The only linux cli program I found was mp3val, however when I run the -f option it reports the file is just fine and dandy.