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• Elixir long running background task doesn't complete, sometimes crashes

  29 mars 2018, par Kulix

  As a little bit of background, I have an endpoint that is responsible for video upload. What I want to do, is copy the video file to a temporary location from the request, and spin up an asynchronous task (ffmpeg shell process) to transcode that video in the background so that my endpoint can return a 200 in a timely manner, and the response does not wait for ffmpeg to finish transcoding that video.

  Here is my code from the controller.

  def create(conn, %{"file" => file ... })
  
      uuid = Video.uuid()
  
      tmp_path = Application.get_env(:myapp, :video_tmp_path) <> "/" <> uuid
  
      :ok = File.cp(file.path, tmp_path)
  
      VideoService.process(tmp_path, final_path)

  The inside of VideoService looks like the following.

  defmodule MyApp.Services do
  
    defmodule VideoService do
  
      def process(tmp_path, final_path) do
  
        Task.start_link fn ->
  
          System.cmd("ffmpeg", ["-i", tmp_path, final_path, "-hide_banner"])
  
          File.rm(tmp_path)
  
        end
  
      end
  
    end
  
  end

  The problem I am having here is that no matter what, nothing past the System.cmd("ffmpeg") call executes in the VideoService, and sometimes the System.cmd call doesn’t even spin up an ffmpeg process. Am I doing something wrong here ? What I need is a way to spin this ffmpeg shell process out in the background from the controller / service and respond with a 200 on video upload. Thanks for help in advance. I am new to elixir / OTP, so I’m sure I’m doing something stupid.

  I also randomly see the following error

  erl_child_setup: failed with error 32 on line 240

• ffmpeg make slideshow with images and videos

  6 avril 2020, par atticus

  I'm trying to make a slideshow with ffmpeg that should contain videos and images. Since as far as I know, ffmpeg cannot do this in one step (which would be of course the preferable step)
I'm breaking it up to make a slideshow of some images and concatenate the resulting video with another video.

  



  The problem with this is that when making a slideshow with ffmpeg (like described here : https://trac.ffmpeg.org/wiki/Slideshow) the framerate is adjusted to make it possible to view one image for a longer time.

  



  Now I've got multiple videos with different framerates to concatenate which is no good (I didn't got it working).

  



  I also tried to make the slideshow with a higher framerate (with -vf fps=25) but I didn't got this working.

  



  (since I have images from different locations/not all images of the current directory should be concatenated at once I really need to use the concat demuxer (as far as I know))

  



  Does someone know how to do this right ?

  



  ---

  



  What I already tried :

  



  ffmpeg -safe 0 -f concat -i tmp -vsync vfr -pix_fmt yuv420p -vf fps=25  output.mkv


  



  with a file tmp looking like this : (see the link above for reference)

  



  file /path/to/file1.JPG
duration 2
file /path/to/file2.JPG
duration 2
file /path/to/file2.JPG


  



  This gives me a video which somehow only the first image.

  



  ---

  



  ffmpeg -safe 0 -f concat -i tmp -vsync vfr -pix_fmt yuv420p output.mkv


  



  with a file tmp looking like this : (see the link above for reference)

  



  file /path/to/file1.JPG
duration 2
file /path/to/file2.JPG
duration 2
file /path/to/file2.JPG


  



  This gives me a file which shows all images at the right rate (everything right up to now) but I'm unable to concatenate it with the right video (25fps) with ffmpeg -safe 0 -f concat -i <(printf "file ${PWD}/%s\n" "output.mkv" "video.mp4") -c copy out.mkv

  



  ---

  



  EDIT : The main problem is the concatenation of these two Files :

  



  $ mediainfo video2.MTS
General
ID                                       : 1 (0x1)
Complete name                            : video2.MTS
Format                                   : MPEG-TS
File size                                : 8.95 MiB
Duration                                 : 8 s 240 ms
Overall bit rate mode                    : Variable
Overall bit rate                         : 9 024 kb/s
FileExtension_Invalid                    : ts m2t m2s m4t m4s tmf ts tp     trp ty

Video
ID                                       : 256 (0x100)
Menu ID                                  : 1 (0x1)
Format                                   : AVC
Format/Info                              : Advanced Video Codec
Format profile                           : High@L4
Format settings                          : CABAC / 4 Ref Frames
Format settings, CABAC                   : Yes
Format settings, Reference frames        : 4 frames
Codec ID                                 : 27
Duration                                 : 8 s 320 ms
Width                                    : 1 920 pixels
Height                                   : 1 080 pixels
Display aspect ratio                     : 16:9
Frame rate mode                          : Variable
Color space                              : YUV
Chroma subsampling                       : 4:2:0
Bit depth                                : 8 bits
Scan type                                : Progressive
Writing library                          : x264 core 159 r2991 1771b55
Encoding settings                        : cabac=1 / ref=3 / deblock=1:0:0 / analyse=0x3:0x113 / me=hex / subme=7 / psy=1 / psy_rd=1.00:0.00 / mixed_ref=1 / me_range=16 / chroma_me=1 / trellis=1 / 8x8dct=1 / cqm=0 / deadzone=21,11 / fast_pskip=1 / chroma_qp_offset=-2 / threads=12 / lookahead_threads=2 / sliced_threads=0 / nr=0 / decimate=1 / interlaced=0 / bluray_compat=0 / constrained_intra=0 / bframes=3 / b_pyramid=2 / b_adapt=1 / b_bias=0 / direct=1 / weightb=1 / open_gop=0 / weightp=2 / keyint=250 / keyint_min=25 / scenecut=40 / intra_refresh=0 / rc_lookahead=40 / rc=crf / mbtree=1 / crf=23.0 / qcomp=0.60 / qpmin=0 / qpmax=69 / qpstep=4 / ip_ratio=1.40 / aq=1:1.00

Audio
ID                                       : 257 (0x101)
Menu ID                                  : 1 (0x1)
Format                                   : AAC LC
Format/Info                              : Advanced Audio Codec Low         Complexity
Format version                           : Version 4
Muxing mode                              : ADTS
Codec ID                                 : 15-2
Duration                                 : 8 s 192 ms
Bit rate mode                            : Variable
Channel(s)                               : 2 channels
Channel layout                           : L R
Sampling rate                            : 48.0 kHz
Frame rate                               : 46.875 FPS (1024 SPF)
Compression mode                         : Lossy
Delay relative to video                  : -21 ms

Menu
ID                                       : 4096 (0x1000)
Menu ID                                  : 1 (0x1)
Duration                                 : 8 s 240 ms
List                                     : 256 (0x100) (AVC) / 257         (0x101) (AAC)
Service name                             : Service01
Service provider                         : FFmpeg
Service type                             : digital television


  



  and

  



  $ mediainfo output.mkv
General
Unique ID                                :     28406040384100140874396026026809692875 (0x155ECDEBB2C5FEFE07B31D86D8B512CB)
Complete name                            : output.mkv
Format                                   : Matroska
Format version                           : Version 4
File size                                : 10.2 MiB
Duration                                 : 6 s 83 ms
Overall bit rate                         : 14.0 Mb/s
Writing application                      : Lavf58.29.100
Writing library                          : Lavf58.29.100
ErrorDetectionType                       : Per level 1

Video
ID                                       : 1
Format                                   : AVC
Format/Info                              : Advanced Video Codec
Format profile                           : High@L6
Format settings                          : CABAC / 4 Ref Frames
Format settings, CABAC                   : Yes
Format settings, Reference frames        : 4 frames
Codec ID                                 : V_MPEG4/ISO/AVC
Duration                                 : 6 s 63 ms
Width                                    : 5 184 pixels
Height                                   : 3 888 pixels
Display aspect ratio                     : 4:3
Frame rate mode                          : Variable
Color space                              : YUV
Chroma subsampling                       : 4:2:0
Bit depth                                : 8 bits
Scan type                                : Progressive
Writing library                          : x264 core 159 r2991 1771b55
Encoding settings                        : cabac=1 / ref=3 /     deblock=1:0:0 / analyse=0x3:0x113 / me=hex / subme=7 / psy=1 /     psy_rd=1.00:0.00 / mixed_ref=1 / me_range=16 / chroma_me=1 / trellis=1 / 8x8dct=1 / cqm=0 / deadzone=21,11 / fast_pskip=1 / chroma_qp_offset=-2 / threads=12 / lookahead_threads=2 / sliced_threads=0 / nr=0 / decimate=1 / interlaced=0 / bluray_compat=0 / constrained_intra=0 / bframes=3 / b_pyramid=2 / b_adapt=1 / b_bias=0 / direct=1 / weightb=1 / open_gop=0 / weightp=2 / keyint=250 / keyint_min=25 / scenecut=40 / intra_refresh=0 / rc_lookahead=40 / rc=crf / mbtree=1 / crf=23.0 / qcomp=0.60 / qpmin=0 / qpmax=69 / qpstep=4 / ip_ratio=1.40 / aq=1:1.00
Default                                  : Yes
Forced                                   : No

Audio
ID                                       : 2
Format                                   : AAC LC
Format/Info                              : Advanced Audio Codec Low         Complexity
Codec ID                                 : A_AAC-2
Duration                                 : 6 s 83 ms
Channel(s)                               : 2 channels
Channel layout                           : L R
Sampling rate                            : 44.1 kHz
Frame rate                               : 43.066 FPS (1024 SPF)
Compression mode                         : Lossy
Writing library                          : Lavc58.54.100 aac
Default                                  : Yes
Forced                                   : No


  


• No output when creating an RTMP stream from an RTP stream with FFmpeg

  28 août 2021, par Simon S

  I am building a service that needs to convert RTP streams into HLS streams. The requirements recently shifted, and I now have to create an RTMP stream from the RTP stream and then convert the RTMP to HLS using two separate FFmpeg processes. The problem is that the RTP to RTMP process doesn't actually output anything to the specified RTMP URL.

  


  Going directly from RTP to HLS with the following command (some options removed for brevity) works as expected :

  


  ffmpeg -f sdp \
       -protocol_whitelist file,udp,rtp \
       -i example.sdp \
       -g 2 \
       -hls_time 2.0 \
       -hls_list_size 5 \
       -vcodec libx264 \
       -acodec aac \
       -f hls chunks/test-master.m3u8



  


  However, converting RTP to RTMP with the following command yields no output, nor does it seem to be receiving any input despite the use of an identical SDP file :

  


  ffmpeg -f sdp \
       -protocol_whitelist pipe,udp,rtp \
       -i example.sdp \
       -g 2 \
       -vcodec libx264 \
       -acodec aac \
       -f flv rtmp://localhost/test-stream



  


  This is an example of what the SDP file looks like :

  


  v=0
o=- 0 0 IN IP4 127.0.0.1
s=Test
c=IN IP4 127.0.0.1
t=0 0
m=audio 37000 RTP/AVPF 97
a=rtpmap:97 opus/48000/2
a=fmtp:97 minptime=10;useinbandfec=1
m=video 37002 RTP/AVPF 96
a=rtpmap:96 H264/90000
a=fmtp:96 level-asymmetry-allowed=1;packetization-mode=1;profile-level-id=64001E


  


  MediaSoup generates the RTP stream, and the ports and host match up. I've verified that there is actually a stream of data coming through the ports in question using nc. There are no error messages. Am I missing something obvious here ?