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• ffmpeg - caching ahead piped input as insurance while maintaining low latency and real-time output

  5 décembre 2020, par hedgehog90

  I'm piping a live transcoded stream into ffmpeg (simplified for brevity) :

  


  mpv playlist --o=- | ffmpeg -re -i - -tune zerolatency -f flv rtmp://blah.com/live

  


  The piped input usually runs above 1x encoding speed, but every now and then it can run a little slower than real-time (just a momentary 0.99x or 0.98x dip).
When this happens, the rtmp server (a popular streaming service with an audience) output will pause momentarily for a couple seconds usually.

  


  To overcome this I want ffmpeg to cache a few seconds in advance, so mpv's output (which outputs at whatever speed it's read, so potentially very fast) can supply ffmpeg with a little extra, and whenever mpv goes a little under 1x speed, there's a little insurance that ffmpeg has cached away. This should be doable while maintaining the lowest possible latency.

  


  Question is, how ?

  


• Started Programming Young

  6 septembre 2011, par Multimedia Mike — Programming

  I have some of the strangest memories of my struggles to jump into computer programming.

  Back To BASIC
  I remember doing some Logo programming on Apple II computers at school in 5th grade (1987 timeframe). But that was mostly driving turtle graphics. Then I remember doing some TRS-80 BASIC in 7th grade, circa 1989. Emboldened by what very little I had learned in perhaps the week or 2 we took in a science class to do this, I tried a little GW-BASIC on my family’s “IBM-PC compatible” computer (they were still called that back then). I still remember what my first program consisted of. Even back then I was interested in manipulating graphics and color on a computer screen. Thus :

  10 color 1
  20 print "This is color 1"
  30 color 2
  40 print "This is color 2"
  ...
  

  And so on through 15 colors. Hey, it did the job– it demonstrated the 15 different colors you could set in text mode.

  What’s FOR For ?
  That 7th grade computer unit in science class wasn’t very thick on computer science details. I recall working with a lab partner to transcribe code listings into a computer (and also saving my work to a storage cassette). We also developed form processing programs that would print instructions to input text followed by an “INPUT I$” statement to obtain the user’s output.

  I remember there was some situation where we needed a brief delay between input and printing. The teacher told us to use a construct of the form :

  10 FOR I = 1 TO 20000
  20 NEXT I
  

  We had to calibrate the number based on our empirical assessment of how long it lasted but I recall that the number couldn’t be much higher than about 32000, for reasons that would become clearer much later.

  Imagine my confusion when I would read and try to comprehend BASIC program code I would find in magazines. I would of course see that FOR..NEXT construct all over the place but obviously not in the context of introducing deliberate execution delays. Indeed, my understanding of one of the fundamental building blocks of computer programming — iteration — was completely skewed because of this early lesson.

  Refactoring
  Somewhere along the line, I figured out that the FOR..NEXT could be used to do the same thing a bunch of times, possibly with different values. A few years after I had written that color program, I found it again and realized that I could write it as :

  10 for I = 1 to 15
  20 color I
  30 print I
  40 next I
  

  It still took me a few more years to sort out the meaning of WHILE..WEND, though.

• FFMPEG -re Insurance

  17 octobre 2020, par Devin Dixon

  FFMPEG -re according to the ffmpeg docs :

  


  


  Read input at native frame rate. Mainly used to simulate a grab
device, or live input stream (e.g. when reading from a file). Should
not be used with actual grab devices or live input streams (where it
can cause packet loss).

  


  


  My ffmpeg stream command is :

  


  ffmpeg -re -i https://www.example.com/video.mp4 -filter_complex tpad=start_duration=10:stop_duration=15:start_mode=add:color=black:stop_mode=add -af adelay=10000|10000 -maxrate 2M -crf 24 -bufsize 6000k -c:v libx264 -preset superfast -tune zerolatency -strict -2 -c:a aac -ar 44100 -attempt_recovery 1 -max_recovery_attempts 5 -drop_pkts_on_overflow 1 -f flv rtmp://live.example.com/123453


  


  Except this does not always work, and sometimes I have livestreams ending early because ffmpeg is playing faster than the frame rate. Is there another command that can be used to ensure ffmpeg streams the video in real time ?