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• given a list of mp4, generate fmp4 and concatenate

  6 août 2021, par onion

  my input is a list of mp4 (for example each one is 10s), each mp4 will have correct timestamp, for example the second mp4 represents from 10s - 20s data.

  


  To simulate my input, I generate a list of mp4 this way

  


  ffmpeg -i ../origin-long-video.mp4 -map 0 -c copy -f segment -segment_time 10 -force_key_frames "expr:gte(t,n_forced*2)" -reset_timestamps 0 videos/output_%03d.mp4


  


  Note I use reset_timestamps 0 so that the timestamp is preserved.

  


  Then I convert each mp4 to fragment mp4 by using

  


  ffmpeg -y   -i videos/output_001.mp4   -force_key_frames "expr:gte(t,n_forced*2)"   -sc_threshold 0   -s 1280x720   -c:v libx264 -b:v 1500k   -c:a copy   -hls_time 100   -hls_playlist_type vod   -hls_segment_type fmp4   -hls_segment_filename "hls1/file%d.m4s"  -copyts hls1/index.m3u8


  


  The above cmd is for the first mp4 file, i did same operation for other mp4 in the list.
Note I used a large hls_time so that each mp4 will result in one fmp4, and also I use copyts to preserve the timestamp.

  


  Then I want to concatenate for example the 2nd and the 3rd fmp4 to generate one mp4, I used

  


  cat init.mp4 > rs.mp4
cat 2nd fmp4 >> rs.mp4
cat 3rd fmp4 >> rs.mp4


  


  However when trying to play the generated rs.mp4, it is 20s black screen then 10s video (corresponding to the 3rd mp4).

  


  I tried another approach which just generated a list of fmp4 directly like this :

  


  ffmpeg -y   -i ../origin-long-video.mp4   -force_key_frames "expr:gte(t,n_forced*2)"   -sc_threshold 0   -s 1280x720   -c:v libx264 -b:v 1500k   -c:a copy   -hls_time 10   -hls_playlist_type vod   -hls_segment_type fmp4   -hls_segment_filename "videos/file%d.m4s"   videos/index.m3u8


  


  And then if I concatenate the 2nd and 3rd generated fmp4 use the same way above, the result mp4 plays well.

  


  I wonder what is the difference between the generated fragment mp4 of the two approach so that they leads to different behavior when concatenation. Thank you !

  


• How to get a list of audio devices in dshow and save

  25 novembre 2016, par H S T

  I use avformat_open_input in ffmpeg to open the audio device, but the second argument to this function is the audio device name, and may not be the full name. So how do I get avformat_open_input (& pFmtCtx, "video = dummy", iformat, & options);
  List of audio device names listed ?Or directly use ffmpeg to open the default audio device ?Thanks.

• Add processing class when initializing file list. Closes #2189.

  4 avril 2013, par blueimp

  m js/main.js
  

  Add processing class when initializing file list. Closes #2189.