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• libavcodec/mpegvideo_enc.c : Fix encoding videos with less frames than the delay of...

  16 octobre 2015, par Alexis Ballier

  libavcodec/mpegvideo_enc.c : Fix encoding videos with less frames than the delay of the encoder.
  When the encoder is fed with less frames than its delay, the picture list looks like  NULL, NULL, ..., frame, frame, frame . When flushing the encoder (input frame == NULL), we need to ensure the picture list is shifted enough so that we do not return an empty packet, which would mean the encoder has finished, while it has not encoded any frame.
  Before the patch, the command :
  
  ’./ffmpeg_g -loglevel debug -f lavfi -i "testsrc=d=0.01" -bf 2 -vcodec mpeg2video out.mxf’ prints :
  Output stream #0:0 (video) : 1 frames encoded ; 0 packets muxed (0 bytes) ;
  After :
  Output stream #0:0 (video) : 1 frames encoded ; 1 packets muxed (8058 bytes) ;
  Relates to ticket #4817.
  Signed-off-by : Michael Niedermayer <michael@niedermayer.cc>
  

  • [DH] libavcodec/mpegvideo_enc.c

• ffmpeg adding a lot of time when concatenating files

  27 novembre 2023, par Jovi Juan

  I'm not sure if this will help anyone else, but I was trying to concatenate some files made in Premiere (problem #1) and ffmpeg kept adding time or changing the timeframe, about an hour for a 37 minute file) which was really frustrating.

  


  I essentially was adding a new credit sequence onto the end and wanted to do it without rerendering any of the sourcefiles which in Premiere takes an amazing 8 hours at 4k and often fails or drops audio or video for no apparent reason.

  


  I tried many many things, but what turned out to be the problem was the timescale, which by using ffprobe, turned out to be two subtly different timescales. Arrrgh. Same program (Premiere), same project.

  


  Anyway the probe results were :
codec_name=h264
r_frame_rate=2997/100

  


  And the other
codec_name=h264
r_frame_rate=30000/1001

  


  So I fixed both of them by running it through this script

  


  ffmpeg -i original.mp4 -c copy -video_track_timescale 30000 output.mp4


  


  where original and output were the respective filenames.

  


  When I ran the concatenation script, it worked !
files.txt :

  


  file 'output.mp4'
file 'output2.mp4'


  


  ffmpeg -f concat -i files.txt -c copy concat-movie.mp4


  


  I can only think that Premiere/Adobe is sneakily doing this to files to make such operations in other programs difficult and frustrating. I even made a sequence using the same files and regenerating the credit sequence from there to ensure the timescales and framerates were the same and it still generated files that were different.

  


  Anyway, that was like a day of work. Hope this saves others the same hassle.

  


• Python unknown file extension .mp4

  18 février 2024, par marlise23

  I am working on a simulation project, however I am unable to create a visual. I started out by running code from matplotlib's documentation (i.e. the code does not belong to me).
When I run the code, I get the error "unknown file extension : .mp4". 
I have installed ffmpeg and checked that it is an updated version.

  



  I am using a Windows computer and Python 3.

  



  import numpy as np
from matplotlib import pyplot as plt
from matplotlib import animation
plt.rcParams['animation.ffmpeg_path']='‪C:\\FFmpeg\bin\ffmpeg.exe'

# First set up the figure, the axis, and the plot element we want to animate
fig = plt.figure()
ax = plt.axes(xlim=(0, 2), ylim=(-2, 2))
line, = ax.plot([], [], lw=2)

# initialization function: plot the background of each frame
def init():
    line.set_data([], [])
    return line,

# animation function.  This is called sequentially
def animate(i):
    x = np.linspace(0, 2, 1000)
    y = np.sin(2 * np.pi * (x - 0.01 * i))
    line.set_data(x, y)
    return line,

# call the animator.  blit=True means only re-draw the parts that have changed.
anim = animation.FuncAnimation(fig, animate, init_func=init,
                               frames=200, interval=20, blit=True)

# save the animation as an mp4.  This requires ffmpeg or mencoder to be
# installed.  The extra_args ensure that the x264 codec is used, so that
# the video can be embedded in html5. 
anim.save('basic_animation.mp4', fps=30, extra_args=['-vcodec', 'libx264'])

plt.show()