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• Should a long Running video processing task to be done client side or server side

  27 avril 2021, par Ritwiz Sinha

  I was creating an application in react for uploading video and using a REST API to send that to the server and store in S3. I also wanted the simple audio version of the video for some other tasks and I am confused as to what might be the better way :

  


  

  1. Creating audio file on the fly when it is needed using node-ffmpeg package and not store it anywhere

  


  2. Start converting the video file to audio on the browser client only, and posting that to the server for storage along with the video.

  


  3. Just post the video to the server and use queue system for creating a new task for video conversion to audio and then save that to the S3 storage.
The second method seems to be saving some compute power on the server but it might be a problem if the video upload completes, audio conversion is still going on and the client disconnects.
Would appreciate some help, thanks.

  


  


• ffmpeg decode example using vda acceleration ?

  18 mars 2015, par Bill Yan

  I’m testing the vda hw accelerated decoder of ffmpeg, but have no luck so far.

  the command line I use is this :

  ./ffmpeg -hwaccel vda -i ~/Downloads/big_buck_bunny_720p_surround.avi -c:v rawvideo -pix_fmt yuv420p out.yuv

  (the input video can be downloaded here : http://mirrorblender.top-ix.org/peach/bigbuckbunny_movies/big_buck_bunny_720p_surround.avi)

  but it uses the sw decoder, instead of the requested vda hw decoder.

  I debugged ffmpeg.c, and found out that in the function get_format :

  if (!(desc->flags & AV_PIX_FMT_FLAG_HWACCEL))
  
      break;

  the desc->flag isn’t set with AV_PIX_FMT_FLAG_HWACCEL, so it skips the hw acceleration initialization.

  the reason is because the pix_fmt is set to AV_PIX_FMT_NONE for some reason, instead of yuv420p as specified by the command.

  I then changed the command to this :

  ./ffmpeg -hwaccel vda -i ~/Downloads/big_buck_bunny_720p_surround.avi -c:v rawvideo -pix_fmt vda_vld out.yuv

  but what I got was :

  Impossible to convert between the formats supported by the filter 'format' and the filter 'auto-inserted scaler 0'
  
  
  
  
  
  Error opening filters!

  Can you please show me an example of using ffmpeg to dump the above video into yuv using the vda hw decoder ?

  UPDATE from the ffmpeg mailist.

  I was told to try the following command instead :

      ./ffmpeg -vcodec h264_vda -i ~/Downloads/big_buck_bunny_720p_surround.avi out.yuv

  but this is what I got :

  ./ffmpeg -vcodec h264_vda -i ~/Downloads/big_buck_bunny_720p_surround.avi out.yuv
  
  
  
  ffmpeg version 2.6.1 Copyright (c) 2000-2015 the FFmpeg developers
  
  built with Apple LLVM version 6.0 (clang-600.0.57) (based on LLVM 3.5svn)
  
  configuration: 
  
  libavutil      54. 20.100 / 54. 20.100
  
  libavcodec     56. 26.100 / 56. 26.100
  
  libavformat    56. 25.101 / 56. 25.101
  
  libavdevice    56.  4.100 / 56.  4.100
  
  libavfilter     5. 11.102 /  5. 11.102
  
  libswscale      3.  1.101 /  3.  1.101
  
  libswresample   1.  1.100 /  1.  1.100
  
  [10:20:50.169] vtDecompressionDuctCreate signalled err=-8973 (err) (Could not select and open decoder instance) at /SourceCache/CoreMedia_frameworks/CoreMedia-1562.107/Sources/VideoToolbox/VTDecompressionSession.c line 1181
  
  [h264_vda @ 0x7f9feb034600] Failed to init VDA decoder: -12473.
  
  [avi @ 0x7f9feb00da00] Failed to open codec in av_find_stream_info
  
  [NULL @ 0x7f9feb034600] missing picture in access unit with size 9960
  
  [10:20:50.252] vtDecompressionDuctCreate signalled err=-8973 (err) (Could not select and open decoder instance) at /SourceCache/CoreMedia_frameworks/CoreMedia-1562.107/Sources/VideoToolbox/VTDecompressionSession.c line 1181
  
  [h264_vda @ 0x7f9feb034600] Failed to init VDA decoder: -12473.
  
  [NULL @ 0x7f9feb034600] missing picture in access unit with size 457

  the reason I wanted to try this was because I wanted to use vda with libavcodec in the first place. but the problem I saw was exactly the above. looks like ffmpeg has the same issue.

• Declaring Variables in ffmpeg in a batch file

  8 juillet 2020, par John Smith

  So I wanted to declare a variable and then use that variable throughout my ffmpeg commands in a batch file. I've seen another question about using the duration of the video, but I want to be able to change the timecode I want to cut at myself.

  


  However, the problem is I don't think I'm declaring the variable properly because it says it 00:52:00 is unrecognised, this is what I've tried so far.

  


  $timecodeToCut = 00:52:00

rem The following command can be used to trim an mp4 file at a specified position. In this example it copies the first 42 minutes of the input.mp4 file and copies it to the output.mp4 file.
ffmpeg -i input.mp4 -c copy -to $timecodeToCut tmpOutput1.mp4


  


  EDIT :
I found this from another answer, but couldn't find much information on how variables work with ffmpeg. Sorry about that, I'm a beginner when it comes to coding, do you happen to know how I could correct it to use it in a batch file ? I've tried using set timecodeToCut = 00:52:00 and then in place of $timecodeToCut used %timecodeToCut%, but it still gives me an error ?