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• Streaming a video using ffmpeg from images during the images generation is still on-going

  1er août 2019, par 박성우

  I’m trying to stream a video to web using ffmpeg. My code creates some random images in same shape and i wanted to stream on web. The problem is that image generation is still on-going when I start to stream the video.

  I found that mp4 format is not a suitable one for streaming and gonna changed it to flv or webm.
  So, that i tried is as bellow.

  ffmpeg -i PATH_TO_IMAGES/%5d.jpg -i MY_AUDIO.WAV output.flv
  
  ffmpeg -i PATH_TO_IMAGES/%5d.jpg -i MY_AUDIO.WAV output.webm

  but my problem comes from,
  first, i could not load images generated after above command is executed.
  second, when i used webm, i should reload the video to get next segment.

  first one is critical. Could anyone advise if there is any way to load images during encoding or other way to go ?

  Thank you.

• 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 ?

  


• 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.