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• avutil/eval : add function to track variable use

  17 novembre 2019, par Gyan Doshi

  avutil/eval : add function to track variable use
  1)Some filters allow cross-referenced expressions e.g. x=y+10. In
  
  such cases, filters evaluate expressions multiple times for
  
  successful evaluation of all expressions. If the expression for one or
  
  more variables contains a RNG, the result may vary across evaluation
  
  leading to inconsistent values across the cross-referenced expressions.
  2)A related case is circular expressions e.g. x=y+10 and y=x+10 which
  
  cannot be succesfully resolved.
  3)Certain filter variables may only be applicable in specific eval modes
  
  and lead to a failure of evaluation in other modes e.g. pts is only
  
  relevant for frame eval mode.
  At present, there is no reliable means to identify these occurrences and
  
  thus the error messages provided are broad or inaccurate. The helper
  
  function introduced - av_expr_count_vars - allows developers to identify
  
  the use and count of variables in expressions and thus tailor the error
  
  message, allow for a graceful fallback and/or decide evaluation order.
  

  • [DH] libavutil/eval.c
  • [DH] libavutil/eval.h
  • [DH] libavutil/version.h

• How to Record a Seekable Video File with Lossless Compression wich is seekable while recording ?

  21 novembre 2024, par Christian Schaffner

  I am using FFmpeg to record a dshow device to a .mkv file. My goal is to use a lossless codec like H.264 or FFV1 for the best quality. Here’s the issue I’m encountering :

  


  In my application, the recorded file needs to be played in another application while recording is still in progress. While playback works, the file is not seekable because the index is written only after the recording ends.

  


  My question :
  
Is there any way to record a video that remains seekable, even if the recording process is incomplete ? I am open to low-filesize, uncompressed formats or other practical solutions that meet these requirements.

  


  Here’s my current FFmpeg command :

  


  ffmpeg -f dshow -i video="Your Video Device" -c:v libx264 -preset ultrafast -crf 0 output.mkv

  


  I've also tried FFV1 as the codec, but the seekability issue persists :

  


  ffmpeg -f dshow -i video="Your Video Device" -c:v ffv1 output.mkv

  


  Things I’ve Tried :

  


  

  1. Using the -movflags +faststart option (applicable to MP4, but not for MKV).

  


  2. Switching container formats to see if other containers might write the index during recording (e.g., AVI or MP4).

  


  3. Exploring streaming protocols (e.g., udp or rtmp) for playback but found these unsuitable for my use case.

  


  


  Requirements :

  


  

  • Lossless video quality (e.g., H.264 lossless or FFV1).

  


  • Seekable playback during recording.

  


  


  Examples

  


  

  1. How to record a seekable H.264 lossless video while still recording ?

  


  2. Can FFV1 (or similar codecs) support live seekable playback during recording ?

  


  


  Does FFmpeg or any container format have a feature or flag that could solve this problem ? Or are there alternative workflows or tools that can help ? Any help or suggestions would be appreciated !

  


  EDIT :
The Reading aplication uses PyAV wich intern uses FFMEG.

  


• Problems with paperclip and ffmpeg

  15 avril 2015, par proeo pre

  I have a problem with update a video for web cam.

  my model :

  has_attached_file :video_presentacion, :styles => { 
  
      :original => { :geometry => "1280x720", :format => 'mp4',:convert_options => { :output => { :vcodec => 'libx264'}} },
  
      :thumb => { :geometry => "350x350#", :format => 'png', :time => 12}
  
  }, :processors => [:ffmpeg]
  
  
  
  
  
  
  
  validates_attachment_content_type :video_presentacion, :content_type => [ 'application/x-mp4','video/mp4',
  
                                                                        'video/mpeg',
  
                                                                        'video/quicktime',
  
                                                                        'video/x-la-asf',
  
                                                                        'video/x-ms-asf',
  
                                                                        'video/x-msvideo',
  
                                                                        'video/x-sgi-movie',
  
                                                                        'video/x-flv',
  
                                                                        'flv-application/octet-stream',
  
                                                                        'video/3gpp',
  
                                                                        'video/3gpp2',
  
                                                                        'video/3gpp-tt',
  
                                                                        'video/BMPEG',
  
                                                                        'video/BT656',
  
                                                                        'video/CelB',
  
                                                                        'video/DV',
  
                                                                        'video/H261',
  
                                                                        'video/H263',
  
                                                                        'video/H263-1998',
  
                                                                        'video/H263-2000',
  
                                                                        'video/H264',
  
                                                                        'video/JPEG',
  
                                                                        'video/MJ2',
  
                                                                        'video/MP1S',
  
                                                                        'video/MP2P',
  
                                                                        'video/MP2T',
  
                                                                        'video/mp4',
  
                                                                        'video/MP4V-ES',
  
                                                                        'video/MPV',
  
                                                                        'video/mpeg4',
  
                                                                        'video/mpeg4-generic',
  
                                                                        'video/nv',
  
                                                                        'video/parityfec',
  
                                                                        'video/pointer',
  
                                                                        'video/raw',
  
                                                                        'video/rtx']

  MY file name have WIN_20150415_103337.MP4

  file have codec h.264
  sonido have codec MPEG-4 AAC

  When I upload in development mode on my laptop, it work fines. When I update on test or production don’t work and log archive...

  [paperclip] An error was received while processing: #tmp/3f143e8fbebaf46e7103d8153e06f17920150415-11490-1buc2jr.MP4' -vcodec libx264 -s 1280x720 -acodec aac -strict experimental -y '/tmp/3f143e8fbebaf46e7103d8153e06f17920150415-11490-1buc2jr20150415-11490-1ww6qqc.mp4'' returned 1. Expected 0

  Here is the command output :

  [paperclip] [ffmpeg] ffprobe "/tmp/3f143e8fbebaf46e7103d8153e06f17920150415-11490-1buc2jr.MP4" 2>&1
  
  
  
  [paperclip] [ffmpeg] Command Success
  
  
  
  
  
  [paperclip] [ffmpeg] Making...
  
  [paperclip] [ffmpeg] Building Destination File: '3f143e8fbebaf46e7103d8153e06f17920150415-11490-1buc2jr' + 'png'
  
  
  
  [paperclip] [ffmpeg] Destination File Built
  
  [paperclip] [ffmpeg] Adding Geometry
  
  [paperclip] [ffmpeg] Extracting Target Dimensions
  
  [paperclip] [ffmpeg] Target Size is Available
  
  [paperclip] [ffmpeg] Keeping Aspect Ratio
  
  [paperclip] [ffmpeg] Pad Only
  
  [paperclip] [ffmpeg] Convert Options: 
  
  [paperclip] [ffmpeg] Adding Format
  
  [paperclip] [ffmpeg] Adding Source
  
  [paperclip] [ffmpeg] Building Parameters
  
  [paperclip] [ffmpeg] -ss 12 -i :source -vf scale=350:-1,pad=350:350:0:77.0:black -vframes 1 -f image2 -y :dest
  
  Command :: PATH=/usr/local/bin/:$PATH; ffmpeg -ss 12 -i '/tmp/3f143e8fbebaf46e7103d8153e06f17920150415-11490-1buc2jr.MP4' -vf scale=350:-1,pad=350:350:0:77.0:black -vframes 1 -f image2 -y '/tmp/3f143e8fbebaf46e7103d8153e06f17920150415-11490-1buc2jr20150415-11490-txzcol.png'
  
  Command :: PATH=/usr/local/bin/:$PATH; file -b --mime '/tmp/3f143e8fbebaf46e7103d8153e06f17920150415-11490-1buc2jr20150415-11490-txzcol.png'
  
  
  
   Command :: PATH=/usr/local/bin/:$PATH; file -b --mime '/tmp/3f143e8fbebaf46e7103d8153e06f17920150415-11490-1kbatzu.MP4'
  
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