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• How do I pass a pipe to ffmpeg ?

  6 novembre 2022, par m_j_alkarkhi

  I want to send a couple of images to ffmpeg and output a video

  


  I have tried to use something similar to this which always seems to finish but when I check the output, it always returns an empty 48b file

  


  I have tried changing the order of the flags but nothing seems to work

  


  Here is my code

  


  using System.Diagnostics;
using SkiaSharp;

Process process = new Process();
process.StartInfo.FileName = @"ffmpeg";
process.StartInfo.Arguments = "-f image2pipe -r 30 -i - /home/user/Videos/test33.mp4";
process.StartInfo.UseShellExecute = false;
process.StartInfo.RedirectStandardInput = true;
process.StartInfo.RedirectStandardOutput = true;
        
process.Start();

for (int i = 0; i < 300; i++)
{
    using var ms = new MemoryStream();
    SKImageInfo imageInfo = new SKImageInfo(1280, 720, SKColorType.Rgba8888);
    using SKSurface surface = SKSurface.Create(imageInfo);
    SKCanvas canvas = surface.Canvas;
    canvas.Clear(SKColor.Parse("#ffffff"));
    using SKImage image = surface.Snapshot();
    using SKData data = image.Encode(SKEncodedImageFormat.Png, 80);
    data.SaveTo(ms);
    ms.WriteTo(process.StandardInput.BaseStream);
}


  


• Ffmpeg saving rtsp stream as mp4 has audio sync issues in Chrome

  28 juin 2020, par user3533414

  I'm saving rtsp stream as mp4 files using ffmpeg using the following command ;

  


  ffmpeg -use_wallclock_as_timestamps 1 -rtsp_transport tcp -i rtsp ://192.168.1.30:8554/Stream1 -vcodec copy -acodec copy -f segment -segment_time 60 -reset_timestamps 1 "test-%01d.mp4"

  


  When I try to play those files on Chrome, audio sync is broken after a while. I get the following warning in chrome ://media-internals/ ;

  


  "Failed to reconcile encoded audio times with decoded output."

  


  I also get the following warning for a couple of files with ffmpeg while saving mp4 ;

  


  Non-monotonous DTS in output stream 0:0 ; previous : ..., current : ... ; changing to .... This may result in incorrect timestamps in the output file.

  


  There's no issues regarding audio sync with video players such as VLC.

  


  This is the information regarding my rtsp stream ;

  


  Duration : N/A, start : 1593340813.628389, bitrate : N/A

  


  Stream #0:0 : Video : h264 (Baseline), yuv420p(tv, progressive), 1280x720, 29.97 fps, 29.97 tbr, 90k tbn, 59.94 tbc

  


  Stream #0:1 : Audio : aac (LC), 24000 Hz, stereo, fltp

  


  How can I overcome the audio sync issue ?

  


• Get a still frame during video capture on Linux

  15 janvier 2020, par Arthur Hebert

  I want to capture video from a webcam (saving to file), and occasionally get the most recent still frame on-demand (from python code), while continuing to capture. Is there a way to do this on Linux ?

  To capture video, I am using the following command :

  ffmpeg -f v4l2 -framerate 30 -video_size 1024x576 -i /dev/video0 myvideo.mp4

  Then in another terminal, I try to capture the latest still frame :

  ffmpeg -sseof -3 -i myvideo.mp4 -update 1 -q:v 1 current_frame.jpg

  I get varied responses from this last command, including

  Cannot use -sseof, duration of myvideo.mp4 not known

  and

  [matroska,webm @ 0x55e1aae26900] Duplicate element
   Last message repeated 2 times

  Constraints :

  1. I need to control the solution from python (e.g. calling ffmpeg via subprocess.Popen) to (a) start recording, (b) get frames at arbitrary points, (c) stop recording.

  Flexibility

  1. The frame timing doesn’t have to be exact. It’s okay for it to be a frame within the last couple seconds.
  2. I am not attached to a particular container format (mkv, mp4, etc.)
  3. I am open to programs other than ffmpeg (it’s nice if it works on Windows too, but not required)