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• How to benchmark the decoding of the frame by ffmpeg ?

  13 juin 2018, par Anny G

  [ What I have done ]

  I am trying to measure a performance of different ffmpeg decoders by

  • timing how long the call to function avcodec_decode_video2(..) takes in ffmpeg.c and running ffmpeg binary the following way

  ~/bin/ffmpeg -benchmark_all -loglevel debug -threads 0 -i ~/Documents/video-input.h264 -c:v libx265 -x265-params crf=25 video-output.hevc

  • and by timing how long the same function takes in ffplay.c and running the ffplay binary the following way

  ~/bin/ffplay ~/Documents/video-input.h264

  In my understanding the average time for the call to that function should be the same whether I am converting the video or playing it, because I am only measuring how long it takes to decode the frame for that video. Is this a wrong way of doing it ? Please let me know if I am incorrect. The results I am getting are strange to me - the call to the aforementioned function takes twice as much in ffmpeg binary compared to ffplay binary. I have tried to run ffmpeg binary with -threads 0 and without it, but the results are still the same(twice as long as ffplay). Could it be because ffplay binary simply utilizes more threads ? When I try it with -threads 1, ffmpeg takes about 10 times as long as ffplay (which makes sense to me since before it was using several threads and now it is only using 1)

  Before I ask my question, I want you to know that I am a beginner in video processing and video encoding/decoding processes.

  [My question]

  I am wondering what would be an accurate way to measure how long it takes to decode a frame (using 1 thread) ? Should I simply measure only how long it takes to call avcodec_decode_video2(..) function using the ffmpeg binary, and not the ffplay binary ? Would the results be more accurate that way ?
  I also tried to enable -benchmark_all -loglevel debug options, but it seems like the following message bench:    64537 decode_video 0.0 is not very helpful if 0.0 is supposed to mean time. (Not sure what the other number means).

• Sending BlackMagic DeckLink Studio 4K over RTMP streams with FFmpeg

  17 novembre 2017, par im dumb

  I’m trying to send a stream of video that’s coming into a BlackMagic DeckLink Studio 4K capture card over a few different RTMP streams at once with FFmpeg. The command that I am doing it with is this :

  ffmpeg -re -format_code Hi59 -f decklink -i 'DeckLink Studio 4K' -map 0 -flags +global_header -vcodec libx264 -crf 25 -preset medium -pix_fmt yuv422p -acodec aac -f tee "[f=flv]rtmp://ip1/live/test|[f=flv]rtmp://ip2/live/test.

  However, whenever I send this video out, I just get color bars when looking at the stream. I tried using a different video source (the testsrc supplied by FFmpeg), and that sends out fine over RTMP to multiple stream destinations.

  Is there something weird with how tee and the decklink stuff work in FFmpeg ? Or is there an issue with my command ?

• FFmpeg, how to skip late input ?

  14 novembre 2017, par user3343357

  I’m running ffmpeg to display incoming stream on a Decklink BlackMagic card with the following command line :

  ffmpeg -y -f ourFmt -probesize 32 -i - -f decklink -preset ultrafast 
  
     -pix_fmt uyvy422 -s 1920x1080 -r 30 -af volume=0.1 -max_delay 10000 
  
       DeckLink Mini Monitor

  Basically I get the video over the internet by UDP and stream it to ffmpeg stdin. Both audio and video streams have pts and dts and are fully in sync, if the connection is good there is no problems.

  However if there are issues with the connection i start getting errors, sometimes the video delay grows significantly, and audio stops working.
  The errors i get are :

  ffmpeg : [decklink @ 0x26cc600] There are not enough buffered video
  frames. Video may misbehave ! ffmpeg : [decklink @ 0x26cc600] There’s no
  buffered audio. Audio will misbehave ! ffmpeg : Last message
  repeated 4 times ffmpeg : [decklink @ 0x26cc600] There are not enough
  buffered video frames. Video may misbehave ! ffmpeg : [decklink @
  0x26cc600] There’s no buffered audio. Audio will misbehave ! ffmpeg :
  Last message repeated 3 times ffmpeg : frame= 5204 fps= 30 q=-0.0
  size=N/A time=00:02:53.76 bitrate=N/A dup=385 drop=5 speed=0.993x
  ffmpeg : [decklink @ 0x26cc600] There’s no buffered audio. Audio will
  misbehave ! ffmpeg : Last message repeated 18 times ffmpeg :
  [decklink @ 0x26cc600] There are not enough buffered video frames.
  Video may misbehave ! ffmpeg : [decklink @ 0x26cc600] There’s no
  buffered audio. Audio will misbehave !

  The problem is when the connection is back to normal, the video keeps misbehaving until I restart the stream. What I want to do is for FFmpeg to skip to the content of the last second and play synchronized video from there, drop all the late data in between, is it possible ?