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• FFmpeg create video from images, insert images as frame from timestamp ?

  29 août 2018, par Hunter_AP

  So I’m trying to extract every frame of a video, then use ffprobe to see when each frame is played within a video, then be able to stitch that video back together using those extracted images and ffprobe output.

  Right now, I have this batch file :

  for %%a in (*.mp4) do (
  
      mkdir "%%~na_images" > NUL
  
      ffmpeg.exe -hide_banner -i "%%a"  -t 100 "%%~na_images\image-%%d.png"
  
      ffprobe.exe "%%a" -hide_banner -show_entries frame=coded_picture_number,best_effort_timestamp_time -of csv > "%%~na_frames.txt"
  
  )

  First, a directory is made for the images.
  Then ffmpeg extracts all the frames of the video to individual PNG files, which are numbered appropriately.
  Lastly, ffprobe sees when each frame is first shown within that video (IE : frame 1 is shown at 0 seconds, but at say 60fps then frame 2 is played at 0.016667 seconds in the video). The output looks like this :

  frame,0.000000,0
  
  frame,0.000000
  
  frame,0.017000,1
  
  frame,0.023220

  Where the first number (IE 0.17000 is the time the second frame appears) and the 2nd number is the frame number.
  Now my problem is using ffmpeg to take each frame and place it in the proper time within the video. I can do this using another language (probably Python), but my best guess is to make a loop to iterate through the ffprobe output file, get the frame time and image number, place that frame at the points that it appears, then move on to the next frame and time placement. Looking at the frame data I used as an example above, it ’d be something like this :

  for line in lines:
  
      mySplit = line.split(',')
  
      # Get image number 0 and insert at time 0.000000

  This is the part that I’m not sure how to do in a coding sense. I can read in and parse the lines of the ffprobe output text file, but I have no idea how to insert the frames at certain points in a video using ffmpeg or similar solutions.

• aarch64 : vp9itxfm : Skip empty slices in the first pass of idct_idct 16x16 and 32x32

  9 janvier 2017, par Martin Storsjö

  aarch64 : vp9itxfm : Skip empty slices in the first pass of idct_idct 16x16 and 32x32
  This work is sponsored by, and copyright, Google.
  Previously all subpartitions except the eob=1 (DC) case ran with
  
  the same runtime :
  vp9_inv_dct_dct_16x16_sub16_add_neon :   1373.2
  
  vp9_inv_dct_dct_32x32_sub32_add_neon :   8089.0
  By skipping individual 8x16 or 8x32 pixel slices in the first pass,
  
  we reduce the runtime of these functions like this :
  vp9_inv_dct_dct_16x16_sub1_add_neon :     235.3
  
  vp9_inv_dct_dct_16x16_sub2_add_neon :    1036.7
  
  vp9_inv_dct_dct_16x16_sub4_add_neon :    1036.7
  
  vp9_inv_dct_dct_16x16_sub8_add_neon :    1036.7
  
  vp9_inv_dct_dct_16x16_sub12_add_neon :   1372.1
  
  vp9_inv_dct_dct_16x16_sub16_add_neon :   1372.1
  
  vp9_inv_dct_dct_32x32_sub1_add_neon :     555.1
  
  vp9_inv_dct_dct_32x32_sub2_add_neon :    5190.2
  
  vp9_inv_dct_dct_32x32_sub4_add_neon :    5180.0
  
  vp9_inv_dct_dct_32x32_sub8_add_neon :    5183.1
  
  vp9_inv_dct_dct_32x32_sub12_add_neon :   6161.5
  
  vp9_inv_dct_dct_32x32_sub16_add_neon :   6155.5
  
  vp9_inv_dct_dct_32x32_sub20_add_neon :   7136.3
  
  vp9_inv_dct_dct_32x32_sub24_add_neon :   7128.4
  
  vp9_inv_dct_dct_32x32_sub28_add_neon :   8098.9
  
  vp9_inv_dct_dct_32x32_sub32_add_neon :   8098.8
  I.e. in general a very minor overhead for the full subpartition case due
  
  to the additional cmps, but a significant speedup for the cases when we
  
  only need to process a small part of the actual input data.
  This is cherrypicked from libav commits
  
  cad42fadcd2c2ae1b3676bb398844a1f521a2d7b and
  
  a0c443a3980dc22eb02b067ac4cb9ffa2f9b04d2.
  Signed-off-by : Michael Niedermayer <michael@niedermayer.cc>
  

  • [DH] libavcodec/aarch64/vp9itxfm_neon.S

• How to parse WMV (ASF) file ? Can't find length of data packets

  9 mars 2018, par bukkojot

  I try to parse WMV (ASF) files without any SDK, just by decoding raw bytes. Now I have problem with ASF_Data_Object, where I can’t find length of data packet. More precise, Single payload data packet.

  See image :
  

  Here I have 9 packets, but unable to find size of individual packet. How I can determine border between packets ?

  I think, my problem at byte 0x411, where field "Length type flags". As you can see, here 0 value, so all flags are zero. Even Packet Length Type.

  
  

  Yes, 0 value here allowed here. But how to read this type of content ?

  This is now compressed payload, as replication data is 8, not 1. So, this is single payload without additional fields of size.

  Sample of WMV file : https://files.catbox.moe/b51l2j.wmv