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• How to efficiently create H264 mpeg from two clips with known different motion intensity ?

  14 février 2017, par Serge

  Given an audio and an image we create a static image "video" and then append a short clip that has a rather intense motion.

  Audio and image varies from run to run. Appended animation is always the same. Rendering is done with ffmpeg on a remote server. Rendered file must be in h264 codec mpg.

  Speed of encoding is crucial. Is there a fast and effective way to generate and merge the two clips quickly ?

  Atm we use the following ffmpeg commands :

  // create first clip from image
  
  ffmpeg -loop 1 -r 24 -i $IMAGE -i $AUDIO -t $AUDIO_LENGTH -c:a aac -profile:a aac_low -ar 48000 -b:a 192k -bsf:a aac_adtstoasc -strict -2 -y -c:v libx264 -profile:v high -preset veryfast  -tune stillimage -crf 24 -x264opts bframes=2 -pix_fmt yuv420p -safe 0  clip1.mpg
  
  // . . .
  
  // then append the animation
  
  ffmpeg -f concat -safe 0 -i list.txt -c copy -y -safe 0 final.mpg 

  Intuition is that we can benefit form knowing exact timing of a first clip with a static image and the second one with intense animation – like it is determined in the 1-st pass of a 2-pass compression.

  Someone experienced in tech of h264 codec and mpeg please advice.

• ffmpeg multiple pipes with different filters and outputs

  3 janvier 2024, par diegoddox

  I'm trying to pipe multiple outputs to an s3 but so far it's only working if I tried with only one pipe as soon as I add more I get Could not write header (incorrect codec parameters ?): Broken pipe error.

  


  aws s3 cp s3://bucket-name/original.mp4 - | \
  ffmpeg -f mp4 -i pipe:0 \
  -vf "scale=1280x720:flags=lanczos" -c:a aac -b:a 96k -movflags frag_keyframe+empty_moov -f mp4 pipe:1 | aws s3 cp - s3://bucket-name/720.mp4 --region my-region \
  -vf "scale=854x480:flags=lanczos" -c:a aac -b:a 96k -movflags frag_keyframe+empty_moov -f mp4 pipe:2 | aws s3 cp - s3://bucket-name/480.mp4 --region my-region \
  -vf "scale=640x360:flags=lanczos" -c:a aac -b:a 96k -movflags frag_keyframe+empty_moov -f mp4 pipe:3 | aws s3 cp - s3://bucket-name/360.mp4 --region my-region \
  -ss 00:00:00 -t 3 -vf "fps=10,scale=720:-1" -movflags frag_keyframe+empty_moov -f gif pipe:4 | aws s3 cp - s3://bucket-name/thumbnail.gif --region my-region


  


  Thanks in advance

  


• How would I assign multiple MMAP's from single file descriptor ?

  9 juin 2011, par Alex Stevens

  So, for my final year project, I'm using Video4Linux2 to pull YUV420 images from a camera, parse them through to x264 (which uses these images natively), and then send the encoded stream via Live555 to an RTP/RTCP compliant video player on a client over a wireless network. All of this I'm trying to do in real-time, so there'll be a control algorithm, but that's not the scope of this question. All of this - except Live555 - is being written in C. Currently, I'm near the end of encoding the video, but want to improve performance.

  To say the least, I've hit a snag... I'm trying to avoid User Space Pointers for V4L2 and use mmap(). I'm encoding video, but since it's YUV420, I've been malloc'ing new memory to hold the Y', U and V planes in three different variables for x264 to read upon. I would like to keep these variables as pointers to an mmap'ed piece of memory.

  However, the V4L2 device has one single file descriptor for the buffered stream, and I need to split the stream into three mmap'ed variables adhering to the YUV420 standard, like so...

  buffers[n_buffers].y_plane = mmap(NULL, (2 * width * height) / 3,
  
                                      PROT_READ | PROT_WRITE, MAP_SHARED,
  
                                      fd, buf.m.offset);
  
  buffers[n_buffers].u_plane = mmap(NULL, width * height / 6,
  
                                      PROT_READ | PROT_WRITE, MAP_SHARED,
  
                                      fd, buf.m.offset +
  
                                      ((2 * width * height) / 3 + 1) /
  
                                      sysconf(_SC_PAGE_SIZE));
  
  buffers[n_buffers].v_plane = mmap(NULL, width * height / 6,
  
                                      PROT_READ | PROT_WRITE, MAP_SHARED,
  
                                      fd, buf.m.offset +
  
                                      ((2 * width * height) / 3 + 
  
                                      width * height / 6 + 1) / 
  
                                      sysconf(_SC_PAGE_SIZE));

  Where "width" and "height" is the resolution of the video (eg. 640x480).

  From what I understand... MMAP seeks through a file, kind of like this (pseudoish-code) :

  fd = v4l2_open(...);
  
  lseek(fd, buf.m.offset + (2 * width * height) / 3);
  
  read(fd, buffers[n_buffers].u_plane, width * height / 6);

  My code is located in a Launchpad Repo here (for more background) :
  http://bazaar.launchpad.net/ alex-stevens/+junk/spyPanda/files (Revision 11)

  And the YUV420 format can be seen clearly from this Wiki illustration : http://en.wikipedia.org/wiki/File:Yuv420.svg (I essentially want to split up the Y, U, and V bytes into each mmap'ed memory)

  Anyone care to explain a way to mmap three variables to memory from the one file descriptor, or why I went wrong ? Or even hint at a better idea to parse the YUV420 buffer to x264 ? :P

  Cheers ! ^^