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• Patching FFmpeg to extract more detailed MV information

  13 février 2018, par helmo

  I am new to video compression and in the past one month I have been studying and reading a lot on this topic. My main aim as of now is to be able to extract in a meaningful way, motion vectors data into a text file.

  Some may write about ffmpeg’s extract_mvs.c but I have already explored this example file and is not returning the complete information I would like to get, for instance, the output of this file does not tell the frame type nor whether a backward or forward motion vector was used for a particular frame number.

  I saw here on SO a similar post that had as answers to explore ’patch’ of FFMpeg to get more meaningful information, that’s a reply from Ronald.

  Is there anyone in the community who can help in expanding this file and get more out of ffmpeg ? Does anyone know about this patch and what it means/entails ?

  Thanks in advance.

• Ffmpeg converting to mp4 from mkv[mpeg@ 0x7f9c19800000] start time for stream 0 is not set in estimate_timings_from_pts

  6 février 2018, par croakouttatune

  I recently converted a number of anime episodes from MKV to MP4 to burn and watch on my SamsungBRPlayer, however during the process I wasn’t able to convert the subtitle stream #0:2 through ffmpeg from .ssa to .srt thru their respective codecs (SSA to MOV_TEXT, can also be SUBRIP). I eventually decided to extract the SSA files and encode them as .srt... one for each episode. I converted these to .srt and plugged them back into the 8 episodes.

  for i in *.mkv;do ffmpeg -i "$i" -i *.srt -c copy -c:s mov_text -c:v h264_videotoolbox -c:a aac -b:a 128k -target ntsc-dvd -y "yfolder/${i%.mkv*}.mp4"; done

  After testing the compatibility of these files I know that this video codec will work, and the BluRay player I use also recognizes the subtitle files ; However , when looking back at the streams #0:0 which is where the subtitles are stored gives me "[mpeg @ 0x7f8621000000] start time for stream 0 is not set in estimate_timings_from_pts." This stream #0:O is now a data stream...0:1 video 0:2 being audio ...
  One of the reasons I thought that I could have received this message is from an Attachment from the original MKV files in the #0:3 stream, which because it wasn’t anything more than metadata I ignored.
  Another would probably be from the code mentioned above importing multiple .srt files into each of the new .mp4 files. I did find a solution however I’m not able to utilize the coding.

  $ for video in *.mkv 
  
  do 
  
  base=${video%.mkv} ffmpeg -i $base.mkv -vf subtitles=$base.srt  
  
  $base-out.mkv ; done

  I couldn’t seem to get it to work. My files were as follows :

  [AnimeGT] Hansom Gold - 001 [720p] [suitup].mp4

  [AnimeGT] Hansom Gold - 002 [720p] [suitup].mp4

  [AnimeGT] Hansom Gold - 003 [720p] [suitup].mp4

  [AnimeGT] Hansom Gold - 004 [720p] [suitup].mp4

  [AnimeGT] Hansom Gold - 005 [720p] [suitup].mp4

  [AnimeGT] Hansom Gold - 006 [720p] [suitup].mp4

  [AnimeGT] Hansom Gold - 007 [720p] [suitup].mp4

  [AnimeGT] Hansom Gold - 008 [720p] [suitup].mp4

  So the titles are obviously fake but whatever. What I need to know is how to use the ${I%.*}.mp4 and ${h%.*}.srt to represent both the base and the video variables in the coding I failed at above.
  While keeping the data stream from each file.
  if that’s the problem. Some help would be nice.

  [mpeg @ 0x7f9c19800000] start time for stream 0 is not set in estimate_timings_from_pts

  I need to know how to deal with this.

• ffmpeg - when scaling, how to keep shapes of people's heads

  19 janvier 2017, par Dave

  Ok, I’m quite familiar with FFMPEG utility in general, and have used it for
  years to cut short snippets from videos, etc. But it’s only in the last
  month that and I decided to learn to use it to transcode with video-filters
  etc. (Before that, I was using other tools such as ’Handbrake’ and ’FreeMake’
  and VLC, etc.)

  For my ffmpeg transcodes, my target output resolution will always be constant, from one transcode run to the next. But the resolution and display aspect-ratio of the input file, from one transcode run to the next, will vary...could be almost any values.
  The input files will never already have black-bars when displayed.

  So, the relevant portion [ i.e. the video-filter(s) part) of my cmd line ] presently is as follows :

  ffmpeg ... -vf "scale=720:406,setsar=1,pad=720:506:0:40:Black" ...

  Also note : I do NOT use the "-aspect" option in the cmd-line. (Maybe I’ll
  need to (???) to solve my issue, but I’m unsure about how that interacts
  with scaling.)

  ( EDIT : Oh, I happen to have chosen that resolution value of 720x406, for
  the image-area (i.e. inside the top/bottom black bars) because it
  has an aspect ratio of 16:9 (Of course, 16:9 ratio is common these days. )

  My cmd always executes cleanly and produces an output file (a WebM, tho I doubt
  that container types and/or vcodec choices matter at all to scaling algorithm issues).

  So the issue/problem that I’m trying to solve is how to prevent any stretching
  in either direction. In other words, a round soccer ball in the input file
  must yield a round ball in the output file ! (NOT oval-shaped in either axis).

  ( Edit #2 : Oh, I forgot to mention that I’m not have the same amount of stretching from one ffmpeg output file to the next. Sometimes there is
  no stretch in my output file, and with some other input file, the
  people are too tall in the output, and some other output file will have
  people are too wide. I’m assuming
  there is some single cmd that will always work for each randomly sized
  input file, WITHOUT having to resort to examining meta-data of each
  input and then having to adjust portions of the needed ffmpeg cmd.
  I assume this because I have used a tool called "FreeMake" that needs
  no such adjustment. When you do a ’scale’ with that program, it asks
  you to choose one of four adjustment-algorithms labeled "original"
  "stretched", "zoom..." and "auto". If I recall correctly, it was the
  "auto" choice that prevented any stretching.)

  The goal of that last filter (i.e. the "pad=720:506:0:40:Black" phrase) is to
  add a black bar of 40 pixels to the top and 60 pixels to the bottom.
  (That filter IS producing the black-bands, as desired. I mention it,
  because I’m unsure whether it could be having any effect on the altered
  shape of the ’round soccer ball’). If the "pad" filter IS part of the
  issue, then maybe I’ll need to make multiple ffmpeg cmds to achieve
  my overall goal (!?!?). [I’d LIKE to be able to do everything in just
  one ffmpeg cmd, as shown.]

  OK ?

  So are there any image-processing and ffmpeg gurus out there that
  know how to fix my problem ?

  TIA...

  Dave