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• FFmpeg function avformat_open_input for USB video device throws exception : No such file or directory

  8 juin, par ffvideoner

  Windows & C# & FFmpeg.AutoGen

  


  I used the ffmpeg-function (from library FFmpeg.AutoGen) to show video from rtsp-stream :

  


  ffmpeg.avformat_open_input(&pFormatContext, "rtsp://127.0.0.1:8554/abc", iformat, null);


  


  It works right.

  


  Now I want to use this function for USB video device.

  


  FFmpeg outputs this device name :

  


  ffmpeg -list_devices true -f dshow -i dummy

[dshow @ 0000000000163000] "GENERAL WEBCAM" (video)


  


  This is how I'm trying to get the video :

  


  string deviceName = "GENERAL WEBCAM";


  


  or

  


  string deviceName = "video=GENERAL WEBCAM";

ffmpeg.avformat_open_input(&pFormatContext, deviceName, ffmpeg.av_find_input_format("dshow"), null);


  


  For both variants of device names, I get an error :

  


  No such file or directory.


  


  But here it works :

  


  ffmpeg -video_size 1280x720 -framerate 30 -f dshow -i video="GENERAL WEBCAM":audio="Microphone (3- GENERAL WEBCAM)" -c:v libx264 -crf 30 -preset ultrafast ffmpegvideo.mp4


  


  Why doesn't avformat_open_input work with video device name ?

  


• Do H264 P&B frames contain pixels values ?

  29 janvier 2019, par Ibrahim Radwan

  From what I understand, the I-frames are the ones containing the actual pixels values, and the P&B frames just contain some kind of indicators on how to construct the next frames from the already decoded frames.

  With that being said, shouldn’t I get a completely blue video, if I’ve only changed the I-frames to be completely blue pictures ?

  Thank you !

• Short HLS MPEG2 Video Segments Do Not Play

  24 août 2019, par Jon H

  I’ve been attempting to cut a video into small segments (words), to be rearranged. While I’ve been able to do it with FFMPEG, cutting into segments and using the fast concat demuxer to reassemble the segments, I am trying to speed it up.

  I have been doing this by splitting the original video into short MPEG2 .ts segments for each word :

  ffmpeg -ss 1 -to 1.5 -i "source.mp4" -c:v libx264 -b:v 1200k -c:a aac -b:a 192k -hls_flags single_file "word.ts"

  I have then tried making a m3u8 playlist of these short video segments, but I found that only segments around 2 seconds or more, play at all.

  I then tried using the ’cat’ command to join these segments into a single file, which I understand should be possible with MPEG2 streams. However, this did not play all the segments either.

  To test if all the segments were present in this concatenated file, I used FFMPEG to convert it back into an MP4 file, and all the segments were present.

  I would appreciate any suggestions on producing the segments, and concatenating individual segments simply without FFMEPG. My project isn’t viable if having to call FFMPEG each time, but would work great if I can simply concatenate words together.