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• Video from VFR Image Sequence

  12 octobre 2014, par Stryker33

  I am using ffmpeg to create video from an image sequence that is taken from the Android Camera’s PreviewCallback method onPreviewFrame...

  The images are written to a pipe that is connected to ffmpeg’s stdin using the command :

  ffmpeg -f image2pipe -vcodec mjpeg -i - -f flv -vcodec libx264

  The problem that’s arising is that the output video is very short as compared to the actual recording time and all of the frames are shown very rapidly...

  But when the frame size is set to the lowest supported preview size, the video appears to be in sync with the actual recording time...

  As far as I reckon this seems to be an issue related to the frame rate of the input image sequence and that of the output video...

  But the main problem is that the frames that are generated from onPreviewFrame are of variable rates...

  Is there any way to construct a smooth video from an image sequence having variable frame rate...?

  Also, the image sequence is muxed with audio from the microphone which also appears to be out of sync with the video...

  Could the video generated using the above process and audio from the microphone be muxed in perfect synchronization...?

• Matplotlib - Why is my saved animation video blank ?

  4 juillet 2022, par Pat X

  This should be pretty simple but I just don't know.

  



  A newbie to Python and FFmpeg. Just trying to save a test video from ArtistAnimation but got blank video.

  



  Before I tried to produce the video, I can see the animation by plt.show() (without "matplotlib.use("Agg")" ). I have already installed FFmpeg in Anaconda as well.

  



  To ensure my FFmpeg is functioning, I used the code from matplotlib example and produced a video that looks perfect. (I guess this means my FFmpeg will work fine from now on ?)

  



  Then, I only changed the figure to my version. Having compared the figure part, I didn't see anything wrong obviously. But in the saved video of my version, it's blank.

  



  import matplotlib
matplotlib.use("Agg")
import matplotlib.pyplot as plt
import matplotlib.animation as ani
import numpy as np
import pandas as pd


fig = plt.figure()
ims = []
for i in range(10):
    ax1 = plt.subplot2grid((2, 2), (0, 0), colspan=2, rowspan=2)
    data = np.random.normal(0, 1, i+1)
    pd.DataFrame(data).plot(kind='bar', ax=ax1)
    ims.append([ax1])



# Set up formatting for the movie files
Writer = ani.writers['ffmpeg']
writer = Writer(fps=15, metadata=dict(artist='Me'), bitrate=1800)

anim = ani.ArtistAnimation(fig, ims, interval=500, repeat_delay=3000, blit=True)
anim.save('textmovie.mp4', writer=writer)
plt.show()


  


• How to make ffmpeg respect the "start_time" variable when combining cdg and mp3 ?

  5 juillet 2020, par Steffen Poulsen

  I'm trying to combine two .cdg and .mp3 files because I want to make a single .mkv file out of them.

  



  When I do it I get a .mkv file alright, but the audio is unfortunately not synced with the video.

  



  So, I was wondering why this is ? Apparently I must be missing a parameter on my command or something.

  



  What I do is this :

  



  ffmpeg -y -i song.cdg -i song.mp3 -pix_fmt yuv420p -vcodec libx264 -acodec copy song.mkv


  



  It works fine, but in this particular case the result is out of sync by 1.2 seconds. This varies per song, from 0 to a couple of seconds.

  



  However, if I do a ffprobe on the .cdg file I notice that this number is already present, as the "start_time" variable :

  



  ffprobe -v error -show_format -show_streams song.cdg
...
start_time=1.186667
...


  



  So, if I just use this number directly as this for the -itsoffset parameter :

  



  ffmpeg -y -itsoffset 1.186667 -i song.cdg -i song.mp3 -pix_fmt yuv420p -vcodec libx264 -acodec copy song.mkv


  



  Then the video and audio is in perfect sync.

  



  So, I am wondering - what parameter do I need to add to my command to have ffmpeg respect this variable ?