The opencv works fine when doing other things. It can open images and show images. But it can't open a video.
The code I'm using to open a video is as below
import cv2
cap = cv2.VideoCapture("MOV_0006.mp4")
while True:
ret, frame = cap.read()
cv2.imshow('video', frame)
if cv2.waitKey(1) & 0xff == ord('q'):
break
cap.release()
cv2.destroyAllWindows()
But when executing, it outputs error messages like below
[h264 @ 0x1053ba0] AVC: nal size 554779904
[h264 @ 0x1053ba0] AVC: nal size 554779904
[h264 @ 0x1053ba0] no frame!
My vlc
and mplayer
can play this video, but the opencv can't.
I have installed x264
and libx264-142
codec package. (using sudo apt-get install
)
My version of ubuntu is 14.04 trusty
.
I'm not sure is it a codec problem or not?
I have rebuilt opencv either with WITH_UNICAP=ON
or with WITH_UNICAP=OFF
, but it doesn't affect the problem at all. The error messages never change.
I converted that mp4
file to an avi
file with ffmpeg
. Then the above opencv code can play that avi
file well.
Therefore I am sure that this is a codec problem.
(I then converted that mp4
file to another mp4
file using ffmpeg
, thinking maybe ffmpeg
would help turning that original unreadable .mp4
codec into a readable .mp4
codec, but the resulting .mp4
file ended up broken. This fact may or may not relate to this problem, just mentioning, in case anybody needs this information.)
Despite knowing this is a codec problem, I tried many other ways but still couldn't solve it. At last I tried rebuilding ffmpeg and opencv, then the problem was solved!
Following is my detailed rebuilding procedure.
(1) Build ffmpeg
FFmpeg website: https://www.ffmpeg.org/download.html
ffmpeg-2.7.1.tar.bz2 link: http://ffmpeg.org/releases/ffmpeg-2.7.1.tar.bz2
tar -xvf ffmpeg-2.7.1.tar.bz2
cd ffmpeg-2.7.1
./configure --enable-pic --extra-ldexeflags=-pie
From http://www.ffmpeg.org/platform.html#Advanced-linking-configuration
If you compiled FFmpeg libraries statically and you want to use them to build your own shared library, you may need to force PIC support (with
--enable-pic
during FFmpeg configure).If your target platform requires position independent binaries, you should pass the correct linking flag (e.g.
-pie
) to--extra-ldexeflags
.
If you encounter error:
yasm/nasm not found or too old. Use --disable-yasm for a crippled build.
Just
sudo apt-get install yasm
Further building options: https://trac.ffmpeg.org/wiki/CompilationGuide/Ubuntu
e.g. Adding option
--enable-libmp3lame
enablespng
encoder. (Before./configure
you need tosudo apt-get install libmp3lame-dev
with version ≥ 3.98.3)
make -j5
(under ffmpeg folder)sudo make install
(2) Build Opencv
wget http://downloads.sourceforge.net/project/opencvlibrary/opencv-unix/2.4.9/opencv-2.4.9.zip
unzip opencv-2.4.9.zip
cd opencv-2.4.9
mkdir build
cd build
cmake -D CMAKE_BUILD_TYPE=RELEASE -D CMAKE_INSTALL_PREFIX=/usr/local -D BUILD_NEW_PYTHON_SUPPORT=ON -D WITH_QT=OFF -D WITH_V4L=ON -D CMAKE_SHARED_LINKER_FLAGS=-Wl,-Bsymbolic ..
You can change those options depend on your needs. Only the last one
-D CMAKE_SHARED_LINKER_FLAGS=-Wl,-Bsymbolic
is the key option. If you omit this one then themake
will jump out errors.This is also from http://www.ffmpeg.org/platform.html#Advanced-linking-configuration (the same link of step 4 above)
If you compiled FFmpeg libraries statically and you want to use them to build your own shared library, you may need to ... and add the following option to your project
LDFLAGS
:-Wl,-Bsymbolic
make -j5
sudo make install
sudo sh -c 'echo "/usr/local/lib" > /etc/ld.so.conf.d/opencv.conf'
sudo ldconfig
Now the opencv code should play a mp4
file well!
WITH_UNICAP=ON
WITH_V4L=ON
when cmake
opencv. But didn't work at all.
cap = cv2.VideoCapture("MOV_0006.mp4")
print cap.get(cv2.cv.CV_CAP_PROP_FOURCC)
I tested this in two environment. In the first environment the opencv works, and in the other the opencv fails to play a video. But both printed out same codec
828601953.0
.I tried to change their codec by
cap.set(cv2.cv.CV_CAP_PROP_FOURCC, cv2.cv.CV_FOURCC(*'H264'))
but didn't work at all.
opencv-2.4.8/3rdparty/lib/
into libraries in my workable environment. But couldn't even successfully build.
I grep
AVC: nal size
and find the libraries contain this error message areopencv-2.4.8/3rdparty/lib/libavcodec.a
etc. That's why I tried to replace them. But it turns out that this is a bad idea.
sudo apt-get -y install libopencv-dev build-essential cmake git libgtk2.0-dev pkg-config python-dev python-numpy libdc1394-22 libdc1394-22-dev libjpeg-dev libpng12-dev libtiff4-dev libjasper-dev libavcodec-dev libavformat-dev libswscale-dev libxine-dev libgstreamer0.10-dev libgstreamer-plugins-base0.10-dev libv4l-dev libtbb-dev libqt4-dev libfaac-dev libmp3lame-dev libopencore-amrnb-dev libopencore-amrwb-dev libtheora-dev libvorbis-dev libxvidcore-dev x264 v4l-utils unzip
Try to install some that thing and some this thing. But it was totally useless.
I've searched the web and there are many similar problems, but NONE of them had a solution!
Below are problems I think the same as mine.
OpenCV/ffmpeg does not play my mp4 video. — from opencv-users.nabble.com
VideoCapture is not working in OpenCV 2.4.2 — from answers.opencv.org
This one mentions rebuilding
ffmpeg
! But the arguments weren't enough for me.
Mp4 reading problem - I installed OpenCV 2.4.1 and python 2.7 and made a short program that reads the avi file successfully. However it fails to read mp4 file. — from answers.opencv.org
Cannot open “.mp4” video files using OpenCV 2.4.3, Python 2.7 in _Windows 7 machine — from Stack Overflow
OpenCV 2.4 VideoCapture not working on Windows — from Stack Overflow