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• Why does OpenCV read video faster than FFMPEG ?

  17 septembre 2022, par tadejsv

  I noticed that OpenCV reads video frames almost 2x faster than FFMPEG.

  


  Why is that ? I thought all OpenCV does is call FFMPEG under the hood, possibly adding its own overhead.

  


  Here's the code I use to obtain these results

  


  import cv2
import time
import numpy as np

cap = cv2.VideoCapture("BigBuckBunny.mp4", apiPreference=cv2.CAP_FFMPEG)
frames = int(cap.get(cv2.CAP_PROP_FRAME_COUNT))

start = time.perf_counter()
while True:
    ret, frame = cap.read()
    if ret is False:
        break
    assert frame.shape == (720, 1280, 3)
    assert frame.dtype == np.uint8
end = time.perf_counter()

print(f"{frames/(end-start):.1f} frames per second")
# Output: 692.3 frames per second

cap.release()


  


  For FFMPEG (using the python-ffmpeg library :

  


  import ffmpeg
import numpy as np
import time

vid_info = ffmpeg.probe("BigBuckBunny.mp4")['streams'][1]
frames = int(vid_info['nb_frames'])

process1 = (
    ffmpeg
    .input("BigBuckBunny.mp4")
    .output('pipe:', format='rawvideo', pix_fmt='bgr24')
)
print(process1.compile())
# Output: ['ffmpeg', '-i', 'BigBuckBunny.mp4', '-f', 'rawvideo', '-pix_fmt', 'bgr24', 'pipe:']


process1 = process1.run_async(pipe_stdout=True)

start = time.perf_counter()
while True:
    in_bytes = process1.stdout.read(1280 * 720 * 3)
    if not in_bytes:
        break
    frame = np.frombuffer(in_bytes, np.uint8).reshape([720, 1280, 3])
end = time.perf_counter()
print(f"{frames/(end-start):.1f} frames per second")
# Output: 373.6 frames per second
process1.wait()


  


  Here's information about the video ( 10 minutes length)

  


  Input #0, mov,mp4,m4a,3gp,3g2,mj2, from 'BigBuckBunny.mp4':
  Metadata:
    major_brand     : mp42
    minor_version   : 0
    compatible_brands: isomavc1mp42
    creation_time   : 2010-01-10T08:29:06.000000Z
  Duration: 00:09:56.47, start: 0.000000, bitrate: 2119 kb/s
  Stream #0:0(und): Audio: aac (LC) (mp4a / 0x6134706D), 44100 Hz, stereo, fltp, 125 kb/s (default)
    Metadata:
      creation_time   : 2010-01-10T08:29:06.000000Z
      handler_name    : (C) 2007 Google Inc. v08.13.2007.
      vendor_id       : [0][0][0][0]
  Stream #0:1(und): Video: h264 (High) (avc1 / 0x31637661), yuv420p, 1280x720 [SAR 1:1 DAR 16:9], 1991 kb/s, 24 fps, 24 tbr, 24k tbn, 48 tbc (default)
    Metadata:
      creation_time   : 2010-01-10T08:29:06.000000Z
      handler_name    : (C) 2007 Google Inc. v08.13.2007.
      vendor_id       : [0][0][0][0]


  


  And FFMPEG and OpenCV versions :

  


  ffmpeg version 4.4.2-0ubuntu0.22.04.1 Copyright (c) 2000-2021 the FFmpeg developers


  


  opencv-python-headless        4.6.0.66


  


• ffmpeg doesnt use all the pictures when creating a video

  9 septembre 2022, par Mikhael Karabas

  I have 75 pictures of the same size for an animation. named 0.png ... 74.png
when running ffmpeg to create a video out of them with 24 fps (commmand and log below) the resulting video instead of expected 75/24 = 3.125 sec. is 2.667 sec in lenght and consists only of first 64 frames(pictures), although ffmpeg tells it has processed 75 frames.
I have checked with

  


  ffmpeg -i output.webm out%%d.png - on the resulting video, it indeed exports 64 first frames and not the rest 11 of them.

  


  Cant undertand what am i doing wrong. please kindly advise.

  


  brief output below.

  


  complete log : https://drive.google.com/file/d/1_J7wLPU9PJZ7jztpiJ8g_bZKPZfiK02L/view?usp=sharing

  


  D:\ffmpeg\ffmpeg-64.exe -report -framerate 24 -f image2 -i %01d.png -c:v libvpx-vp9 -pix_fmt yuva420p -crf 10 -b:v 0 output.webm
ffmpeg started on 2022-09-09 at 19:03:15
Report written to "ffmpeg-20220909-190315.log"
Log level: 48
ffmpeg version 2021-12-17-git-b780b6db64-essentials_build-www.gyan.dev Copyright (c) 2000-2021 the FFmpeg developers
  built with gcc 11.2.0 (Rev2, Built by MSYS2 project)
  configuration: --enable-gpl --enable-version3 --enable-static --disable-w32threads --disable-autodetect --enable-fontconfig --enable-iconv --enable-gnutls --enable-libxml2 --enable-gmp --enable-lzma --enable-zlib --enable-libsrt --enable-libssh --enable-libzmq --enable-avisynth --enable-sdl2 --enable-libwebp --enable-libx264 --enable-libx265 --enable-libxvid --enable-libaom --enable-libopenjpeg --enable-libvpx --enable-libass --enable-libfreetype --enable-libfribidi --enable-libvidstab --enable-libvmaf --enable-libzimg --enable-amf --enable-cuda-llvm --enable-cuvid --enable-ffnvcodec --enable-nvdec --enable-nvenc --enable-d3d11va --enable-dxva2 --enable-libmfx --enable-libgme --enable-libopenmpt --enable-libopencore-amrwb --enable-libmp3lame --enable-libtheora --enable-libvo-amrwbenc --enable-libgsm --enable-libopencore-amrnb --enable-libopus --enable-libspeex --enable-libvorbis --enable-librubberband
  libavutil      57. 11.100 / 57. 11.100
  libavcodec     59. 14.100 / 59. 14.100
  libavformat    59. 10.100 / 59. 10.100
  libavdevice    59.  0.101 / 59.  0.101
  libavfilter     8. 20.100 /  8. 20.100
  libswscale      6.  1.101 /  6.  1.101
  libswresample   4.  0.100 /  4.  0.100
  libpostproc    56.  0.100 / 56.  0.100
Input #0, image2, from '%01d.png':
  Duration: 00:00:03.13, start: 0.000000, bitrate: N/A
  Stream #0:0: Video: png, rgba(pc), 300x400, 24 fps, 24 tbr, 24 tbn
File 'output.webm' already exists. Overwrite? [y/N] y
Stream mapping:
  Stream #0:0 -> #0:0 (png (native) -> vp9 (libvpx-vp9))
Press [q] to stop, [?] for help
[libvpx-vp9 @ 000002dad505c8c0] v1.11.0-62-g7f45e94d9
Output #0, webm, to 'output.webm':
  Metadata:
    encoder         : Lavf59.10.100
  Stream #0:0: Video: vp9, yuva420p(tv, progressive), 300x400, q=2-31, 24 fps, 1k tbn
    Metadata:
      encoder         : Lavc59.14.100 libvpx-vp9
    Side data:
      cpb: bitrate max/min/avg: 0/0/0 buffer size: 0 vbv_delay: N/A
frame=   75 fps=9.9 q=0.0 Lsize=    1056kB time=00:00:02.58 bitrate=3347.2kbits/s speed=0.342x
video:1036kB audio:0kB subtitle:0kB other streams:0kB global headers:0kB muxing overhead: 1.942318%


  


• How to convert AAC/MP4A to MP3 using FFMPEG in full length ? Audio file gets cut off after 1 second

  6 novembre 2022, par Avatar

  I have recorded an audio file with MediaRecorder on iPhone.

  


  As ffmpeg command I am using :

  


  ffmpeg -i 18380889311644327118 -ar 44100 -ac 2 -b:a 128k -c:a libmp3lame -q:a 0 18380889311644327118.mp3


  


  -i specifies the input file
-vn disables all video-streams from the input
-ar audio sampling frequency
-ac number of audio channels
-b:a bit rate
-c:a libmp3lame - codec of target file
-q:a quality set audio quality (codec-specific) (lower is better), see https://superuser.com/a/1515841

-sn disables all subtitle-streams from the input
-dn disables all data-streams from the input


  


  The console output looks like this :

  


  Input #0, mov,mp4,m4a,3gp,3g2,mj2, from '18380889311644327118':
  Metadata:
    major_brand     : iso5
    minor_version   : 1
    compatible_brands: isomiso5hlsf
    creation_time   : 2021-12-08T15:44:06.000000Z
  Duration: 00:00:01.00, start: 0.000000, bitrate: 2258 kb/s
    Stream #0:0(und): Audio: aac (LC) (mp4a / 0x6134706D), 44100 Hz, mono, fltp, 2234 kb/s (default)
    Metadata:
      creation_time   : 2021-12-08T15:44:06.000000Z
      handler_name    : Core Media Audio
Stream mapping:
  Stream #0:0 -> #0:0 (aac (native) -> mp3 (libmp3lame))

Output #0, mp3, to '18380889311644327118.mp3':
  Metadata:
    major_brand     : iso5
    minor_version   : 1
    compatible_brands: isomiso5hlsf
    TSSE            : Lavf58.29.100
    Stream #0:0(und): Audio: mp3 (libmp3lame), 44100 Hz, stereo, fltp, 128 kb/s (default)
    Metadata:
      creation_time   : 2021-12-08T15:44:06.000000Z
      handler_name    : Core Media Audio
      encoder         : Lavc58.54.100 libmp3lame
size=      17kB time=00:00:01.01 bitrate= 135.5kbits/s speed=37.2x
video:0kB audio:16kB subtitle:0kB other streams:0kB global headers:0kB muxing overhead: 3.343701%


  


  As you can see, the duration is 01.00 second. And this happens with all recorded files.

  


  How to convert the entire file (which is 12 seconds long) to its full length ?

  

  

  


  Note : It seems that the recorded file does not have a length specified. Under Windows I renamed the file, adding an extension ".m4a" and opened the file properties :

  


  

  


  The length attribute is empty.