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• How to effectively kill a frozen subprocess in Python ?

  2 janvier 2014, par Konos5

  I am dealing with a rather odd issue.

  I've written a Python wrapper (in Python 2.6.6) for a year old version of ffmpeg. The problem is that given a very particular video, ffmpeg stops working normally (clunky output, full cpu usage, no end stage etc) and takes the python interpreter down with it.

  Now, if I run ffmpeg with my encoding options directly from a terminal and the problematic video as input, ffmpeg won't immediately respond to Ctrl-c. I'll have to wait for a hefty of 10 seconds or more before it exits and gives me back the prompt. However if I use a 'healthy' video instead, it will simply print Received signal 2: terminating. and gracefully exit.

  In the python wrapper I use p.kill() to no effect. The behavior is exactly the same a.k.a I have to wait 10 sec before the program exits. How can I immediately stop ffmpeg when it freezes with some problematic video ?

  Note that if I do a double Ctrl-c I get the prompt back immediately no matter what.

• Create mp4 file from raw h264 using a pipe instead of files

  16 avril 2019, par Charlie Burns

  I have a raw h264 file that I can display with VLC, on a mac :

  open -a VLC file.h264

  I can convert this to mp4 with the command line

  ffmpeg -f h264 -i file.h264 -c:v copy file.mp4

  But what I really want to do is something like :

  cat file.h264 | ffmpeg > file.mp4

  Reason being that the input is coming over a socket and I want to convert it and send it to a video tag in an html file on the fly.

  An alternative solution would be a way to display the raw h264 in a web page without converting it to mp4 first.

  The input is coming in frame by frame, the first four bytes are 0,0,0,1. My understanding is that this h264 Annex B format.

  I know nothing about video formats, I would grateful to be pointed in a direction to look.

  Should I look into writing code using libavcodec like this quuesion or is there an off-the-shelf solution ?

  H.264 muxed to MP4 using libavformat not playing back

  Thanks !

• Fallback input for ffmpeg

  22 septembre 2018, par Daniel Cantarin

  I’m doing some transcoding from a third-party remote input stream that I do not control.

  This input stream has errors from time to time, that I would like to mitigate before sending the stream to my transcoding pipeline, avoiding this way some possible problems in the output.

  I have several ideas regarding different problems. But the most basic scenario I would like to set up is as follows : when the stream is down, or it somehow loses some frames, I want to fill that video gap with a secondary input (like a blank screen, for example).

  For this simple task, I would like to use ffmpeg. I know it can mix, let’s say, an input stream with a fullscreen black square static image. However, I have to deal with this other condition : ffmpeg would run in the same infraestructure for the actual transcoding pipeline. That infraestructure must use its computing power for rendering the output. So, whatever ffmpeg command I end up using should use the minimum possible computing power.

  My actual problem : if I use -vcodec copy, in order to use minimum CPU, I can’t alter the original stream. But if I alter the original stream (by mixing it with some other stream), the operation uses CPU.

  My question : Is there a way to use -vcodec copy, but with a fallback input (instead of a mixed one) for when there are video gaps in the primary stream ?

  Thanks in advance.