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• ffmpeg encode timestamp on a timelapse video

  20 avril 2023, par Kyeotic

  I have a video that is a timelapse (generated by a GoPro, if that matters) with images every 5 seconds. I want to encode a timestamp onto it. Previously I've used a command like this one to get a timestamp burned in

  


  # Convert the date to EPOCH. This will be used to set the time for the draw text
# method.
EPOCH=$(date --date="${STARTDATE}" +%s)

# we assume that the STARTDATE is in UTC 0000, Zulu time, GMT and that we want
# to convert it to the local time on the computer.
ffmpeg -i "${INPUT}" -vf drawtext="fontsize=30:fontcolor=yellow:text='%{pts\:localtime\:${EPOCH}}':x=(w-text_w) - 10:y=(h-text_h) - 10" -vcodec libx265 -crf 28 "${OUTPUT}"


  


  The issue is that the timestamps generated by this progress as if it is a normal video, stamping a 30 minute timelapse as if it were 25 seconds. What I want are timestamps that match the timelapse.

  


  I've looked at the drawtext docs. I thought rate might be the key, but 1/5 and 150 both produce errors like this one :

  


  Parsed_drawtext_0 @ 0x10c607370] Failed to parse expression: (h-text_h) - 10 r=1/5 


  


  I figure I might need to multiply the current frame value to get the correct time, but I don't know how to do that.

  


• Transcode Video to play on a raspberry pi (3/4) with ffmpeg

  20 octobre 2022, par exa.byte

  For a while now I transcode videos to play on a raspberry pi 3 (or 4) but the performance was always really bad.
After a long process of trial and error I found a command which works good most of the time for the various inputs I get from the colleagues :

  


  ffmpeg -i video_input.mp4 -c:v libvpx-vp9 -vf "scale=1280:720" -r 30 -b:v 1.0M -maxrate 1.2M -bufsize 1M video_output.mp4

  


  Today I got a 4k Video, 1.7gb and about 3 minutes with 50fps.

  


  The resulting video has 31MegaBytes. That alone was really concerning but the main problem is, the Video is not playing not even close to smoothly. It's a diashow.

  


  I use a debian bullseye (headless) on an old Z440 machine. So only a CLI is available.
Can some please help me to find a codec which is suitable for playback on a rpi3 or rpi4 ?

  


  I also tried h264_omx as the c:v command but it throws this error :

  


  libOMX_Core.so not found
libOmxCore.so not found


  


  I found posts around that this is already deprecated anyway. So I hope to
find a hero which knows how to transcode this kind of video.

  


  FFMPEG is version 4.3

  


• Start ffmpeg sound recording at system start doesn't work

  3 octobre 2022, par CheatingBoy

  I made a python script to record sound at System boot, but it doesn't work. I've tried using crontab and systemd but it doesn't work. If I start the program manually it works out fine.

  


  #!/bin/python3
import RPi.GPIO as GPIO
import time
import datetime
import subprocess
import os
import signal
GPIO.setmode(GPIO.BCM)
GPIO.setup(24, GPIO.IN)
GPIO.setup(23, GPIO.OUT)
print("Started Sound_Recorder_ULtimate_Control")
p = None
while True:
        time.sleep(0.5)
        if GPIO.input(24) == 1:
            if p is None:
                print("Preparing to recorde")
                today = datetime.datetime.now()
                time1 = "{}.{}.{}_{}:{}:{}".format(today.day , today.month, today.year, today.hour, today.minute, today.second)
                # Aufname starten
                command = "sh -c 'ffmpeg -f pulse -nostdin -i alsa_input.usb-FuZhou_Kingwayinfo_CO._LTD_TONOR_TC30_Audio_Device_20200707-00.mono-fallback /home/pi/sound_recorder/Recordes/'" + time1 + ".mp3"
                print(command)
                #subprocess.Popen(command)
                p = subprocess.Popen(command, stdout=subprocess.PIPE, 
                       shell=True, preexec_fn=os.setsid)
                print("Recording...")
                GPIO.output(23, GPIO.HIGH)
                time.sleep(2)    

            else:
                print("Terminate")
                os.killpg(os.getpgid(p.pid), signal.SIGTERM)
                GPIO.output(23, GPIO.LOW)
                p = None
                time.sleep(2)