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• Realtime removal of carriage return in shell

  1er mai 2013, par Seth

  For context, I'm attempting to create a shell script that simplifies the realtime console output of ffmpeg, only displaying the current frame being encoded. My end goal is to use this information in some sort of progress indicator for batch processing.

  For those unfamiliar with ffmpeg's output, it outputs encoded video information to stdout and console information to stderr. Also, when it actually gets to displaying encode information, it uses carriage returns to keep the console screen from filling up. This makes it impossible to simply use grep and awk to capture the appropriate line and frame information.

  The first thing I've tried is replacing the carriage returns using tr :

  $ ffmpeg -i "ScreeningSchedule-1.mov" -y "test.mp4" 2>&1 | tr '\r' '\n'

  This works in that it displays realtime output to the console. However, if I then pipe that information to grep or awk or anything else, tr's output is buffered and is no longer realtime. For example : $ ffmpeg -i "ScreeningSchedule-1.mov" -y "test.mp4" 2>&1 | tr '\r' '\n'>log.txt results in a file that is immediately filled with some information, then 5-10 secs later, more lines get dropped into the log file.

  At first I thought sed would be great for this : $ # ffmpeg -i "ScreeningSchedule-1.mov" -y "test.mp4" 2>&1 | sed 's/\\r/\\n/', but it gets to the line with all the carriage returns and waits until the processing has finished before it attempts to do anything. I assume this is because sed works on a line-by-line basis and needs the whole line to have completed before it does anything else, and then it doesn't replace the carriage returns anyway. I've tried various different regex's for the carriage return and new line, and have yet to find a solution that replaces the carriage return. I'm running OSX 10.6.8, so I am using BSD sed, which might account for that.

  I have also attempted to write the information to a log file and use tail -f to read it back, but I still run into the issue of replacing carriage returns in realtime.

  I have seen that there are solutions for this in python and perl, however, I'm reluctant to go that route immediately. First, I don't know python or perl. Second, I have a completely functional batch processing shell application that I would need to either port or figure out how to integrate with python/perl. Probably not hard, but not what I want to get into unless I absolutely have to. So I'm looking for a shell solution, preferably bash, but any of the OSX shells would be fine.

  And if what I want is simply not doable, well I guess I'll cross that bridge when I get there.

• Bash script : Cycle script until ffmpeg command restarts successfully

  13 août 2023, par Bellacoda

  I have a IP Camera and the recordings are saved with ffmpeg RTSP into a raspberry pi.

  


  Sometimes, when the electricity shuts off and comes back on, the raspberry boots faster than the IP Camera and the ffmpeg command (saved on a crontab to run every reboot) fails to execute because it can't reach the IP Camera (that is still turning on).

  


  I tried to put a sleep command before the command but that doesn't work either.

  


  It also happened that when the IP Camera reboots, the raspberry closes the command, but when the camera comes back online, I have to manually lauch the command.

  


  Is there a way to make a script that waits to run the ffmpeg command until the camera is fully online (I assume with the $ ? variable for command exit status), and to wait to restart the ffmpeg command when the camera reboots ?

  


  The setup I have now is a crontab :
SHELL=/bin/bash
@reboot sleep 120s ; sudo ffmpeg ...

  


• What is video timescale, timebase, or timestamp in ffmpeg ? [on hold]

  11 avril 2017, par Please Help

  There does not seem to be any explanation online as to what these are. People talk about them a lot. I just want to know what they are and why they are significant. Using -video_track_timescale, how would I determine a number for it ? Is it random ? Should it be 0 ?