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• How to compress video in android faster ?

  21 avril 2017, par Qandeel Abbasi

  I have recently used ffmpeg library for android to compress the video of length 10 seconds and size nearly 25 MB. Following are the commands i tried to use :

  ffmpeg -i /video.mp4 -vcodec h264 -b:v 1000k -acodec mp2 /output.mp4

  OR

  ffmpeg -i input.mp4 -vcodec h264 -crf 20 output.mp4

  Both of the commands were too slow. I canceled the task before it completed because it was taking too much time. It took more than 8 minutes to process JUST 20% of the video. Time is really critical for me so i can’t opt for ffmpeg. I have following question :

  • Is there something wrong with the command or ffmpeg is slow anyway ?
  • If its slow then is there any other well documented and reliable way/library for video compression that i can use in android ?

• Slowing down audio using FFMPEG

  24 janvier 2020, par Maxim_A

  For example I have a source file which is the duration of 6.40 seconds.
  I divide this duration into 10 sections. Then each section is slowed down by a certain value. This works great.

  ffmpeg.exe -i preresult.mp4 -filter_complex 
  
  "[0:v]trim=0:0.5,setpts=PTS-STARTPTS[vv0]; 
  
  [0:v]trim=0.5:1,setpts=PTS-STARTPTS[vv1]; 
  
  [0:v]trim=1:1.5,setpts=PTS-STARTPTS[vv2]; 
  
  [0:v]trim=1.5:2,setpts=PTS-STARTPTS[vv3]; 
  
  [0:v]trim=2:2.5,setpts=PTS-STARTPTS[vv4]; 
  
  [0:v]trim=2.5:3,setpts=PTS-STARTPTS[vv5]; 
  
  [0:v]trim=3:3.5,setpts=PTS-STARTPTS[vv6]; 
  
  [0:v]trim=3.5:4,setpts=PTS-STARTPTS[vv7]; 
  
  [0:v]trim=4:4.5,setpts=PTS-STARTPTS[vv8]; 
  
  [0:v]trim=4.5:6.40,setpts=PTS-STARTPTS[vv9];
  
  
  
  [vv0]setpts=PTS*2[slowv0];
  
  [vv1]setpts=PTS*4[slowv1];
  
  [vv2]setpts=PTS*5[slowv2];
  
  [vv3]setpts=PTS*2[slowv3];
  
  [vv4]setpts=PTS*3[slowv4];
  
  [vv5]setpts=PTS*6[slowv5];
  
  [vv6]setpts=PTS*3[slowv6];
  
  [vv7]setpts=PTS*5[slowv7];
  
  [vv8]setpts=PTS*2[slowv8];
  
  [vv9]setpts=PTS*6[slowv9];
  
  
  
  [slowv0][slowv1][slowv2][slowv3][slowv4][slowv5][slowv6][slowv7][slowv8][slowv9]concat=n=10:v=1:a=0[v1]"  
  
  -r 30 -map "[v1]" -y result.mp4

  Then I needed to slow down along with the video and audio stream. In the documentation I found out about the atempo filter. The documentation says that the extreme boundaries of the value of this filter are from 0.5 to 100. To slow down by half, you need to use the value 0.5. I also learned that if you need to slow down the audio by 4 times, then you just need to apply two filters.

  [aa0]atempo=0.5[aslowv0] //Slowdown x2
  
  [aa0]atempo=0.5, atempo=0.5[aslowv0] //Slowdown x4

  Question 1 :
  How can i slow down audio an odd number of times ? for example, slow down audio by 3.5.7 times. There is no explanation of this point in the documentation.

  Question 2 :
  Do i understand correctly that if you slow down separately the audio stream and the video stream, they will have the same duration ?

  Thank you all in advance !

• FFmpeg av_read_frame not reading frames properly ?

  2 août 2016, par Sir DrinksCoffeeALot

  Alright, so I’ve downloaded some raw UHD sequences in .yuv format and encoded them with ffmpeg in .mp4 container (h264 4:4:4, 100% quality, 25fps). When i use ffprobe to find out how many frames are encoded i get 600, so that’s 24 secs of video.

  BUT, when i run those encoded video sequences through av_read_frame i only get like 40-50% of frames processed before av_read_frame returns error code -12. So I’m wild guessing that there are some data packages in middle of the streams which get read by av_read_frame and forces a function to return -12.

  What my questions are, how should i deal with this problem so i can encode full number of frames (600) ? When av_read_frame returns value different from 0 should i av_free_packet and proceed to read next frame ? Since av_read_frame returns values < 0 for error codes, which error code is used for EOF so i can insulate end of file code ?