How do you identify the codec of a .mp4 video file in Xcode?

sjsu_alumna · July 25, 2021, 1:59am

I tried

cv::VideoCapture cap( argv[1] );
unsigned f = (unsigned)cap.get( cv::CAP_PROP_FOURCC );
cout << "f: " << f << endl;

but output of f was 0. The codec of the video file is H.264.

crackwitz · July 25, 2021, 4:24pm

berak · July 25, 2021, 4:45pm

you should at least query, if your capture opened at all:

cv::VideoCapture cap(argv[1] );
if (! cap.isOpened()) ....

sjsu_alumna · July 25, 2021, 10:30pm

I was able to play the video using OpenCV. I’m wondering if the problem is related to ffmpeg, as suggested by the 1st answer in https://stackoverflow.com/questions/47858206/c-opencv-3-4-ffmpeg-3-4-1-videowriter-and-mp4-output-file-format/54138523

berak · July 26, 2021, 5:21am

no, it is not related. you’re not using a Videowriter, and while writing h264 has a liceense problem, reading is free.

crackwitz · July 27, 2021, 7:55am

since you say this is osx, the video backend might be AVFoundation, not ffmpeg.

do cap.get(cv::CAP_PROP_BACKEND)

sjsu_alumna · July 28, 2021, 4:51am

I tried CAP_PROP_BACKEND and now the output of f is 1200. The next lines of code are:

char fourcc[] = { (char) f, (char)(f >> 8), 
                  (char)(f >> 16), (char)(f >> 24),
                  '\0' };
cout << "fourcc: " << fourcc << endl;

Output of fourcc is \260, but it should be avc1, so I don’t think CAP_PROP_BACKEND gives the fourcc codec.

crackwitz · July 28, 2021, 5:35am

it doesn’t. CAP_PROP_BACKEND tells you the backend.

1200 is CAP_AVFOUNDATION

all your troubles stem from that.

open a VideoCapture with explicit apiPreference… with CAP_FFMPEG

sjsu_alumna · July 28, 2021, 7:14am

I tried:

  cv::VideoCapture cap;
  cap.open( string(argv[1]), cv::CAP_FFMPEG );
  if( !cap.isOpened() ) {
      cout << "Couldn't open capture." << endl;
      return -1;
  }

and the output was “Couldn’t open capture.”

crackwitz · July 28, 2021, 3:42pm

std::cout << cv::getBuildInformation();

sjsu_alumna · August 1, 2021, 1:16am

I tried:

cout << cv::getBuildInformation() << endl;

and the output was:

General configuration for OpenCV 3.4.14-dev =====================================
Version control: 3.4.14-17-g6f70b0524a

Extra modules:
Location (extra): /Users/myname/opencv_contrib/modules
Version control (extra): 3.4.14-7-g31c657e0

Platform:
Timestamp: 2021-04-13T01:15:18Z
Host: Darwin 19.6.0 x86_64
CMake: 3.20.1
CMake generator: Unix Makefiles
CMake build tool: /usr/bin/make
Configuration: RELEASE

CPU/HW features:
Baseline: SSE SSE2 SSE3 SSSE3 SSE4_1
requested: DETECT
Dispatched code generation: SSE4_2 FP16 AVX AVX2 AVX512_SKX
requested: SSE4_1 SSE4_2 AVX FP16 AVX2 AVX512_SKX
SSE4_2 (2 files): + POPCNT SSE4_2
FP16 (1 files): + POPCNT SSE4_2 FP16 AVX
AVX (6 files): + POPCNT SSE4_2 AVX
AVX2 (30 files): + POPCNT SSE4_2 FP16 FMA3 AVX AVX2
AVX512_SKX (7 files): + POPCNT SSE4_2 FP16 FMA3 AVX AVX2 AVX_512F AVX512_COMMON AVX512_SKX

C/C++:
Built as dynamic libs?: YES
C++ Compiler: /Library/Developer/CommandLineTools/usr/bin/c++ (ver 12.0.0.12000032)
C++ flags (Release): -fsigned-char -W -Wall -Werror=return-type -Werror=non-virtual-dtor -Werror=address -Werror=sequence-point -Wformat -Werror=format-security -Wmissing-declarations -Wmissing-prototypes -Wstrict-prototypes -Wundef -Winit-self -Wpointer-arith -Wshadow -Wsign-promo -Wuninitialized -Wno-delete-non-virtual-dtor -Wno-unnamed-type-template-args -Wno-comment -fdiagnostics-show-option -Wno-long-long -Qunused-arguments -Wno-semicolon-before-method-body -ffunction-sections -fdata-sections -fvisibility=hidden -fvisibility-inlines-hidden -O3 -DNDEBUG -DNDEBUG
C++ flags (Debug): -fsigned-char -W -Wall -Werror=return-type -Werror=non-virtual-dtor -Werror=address -Werror=sequence-point -Wformat -Werror=format-security -Wmissing-declarations -Wmissing-prototypes -Wstrict-prototypes -Wundef -Winit-self -Wpointer-arith -Wshadow -Wsign-promo -Wuninitialized -Wno-delete-non-virtual-dtor -Wno-unnamed-type-template-args -Wno-comment -fdiagnostics-show-option -Wno-long-long -Qunused-arguments -Wno-semicolon-before-method-body -ffunction-sections -fdata-sections -fvisibility=hidden -fvisibility-inlines-hidden -g -O0 -DDEBUG -D_DEBUG
C Compiler: /Library/Developer/CommandLineTools/usr/bin/cc
C flags (Release): -fsigned-char -W -Wall -Werror=return-type -Werror=non-virtual-dtor -Werror=address -Werror=sequence-point -Wformat -Werror=format-security -Wmissing-declarations -Wmissing-prototypes -Wstrict-prototypes -Wundef -Winit-self -Wpointer-arith -Wshadow -Wsign-promo -Wuninitialized -Wno-delete-non-virtual-dtor -Wno-unnamed-type-template-args -Wno-comment -fdiagnostics-show-option -Wno-long-long -Qunused-arguments -Wno-semicolon-before-method-body -ffunction-sections -fdata-sections -fvisibility=hidden -fvisibility-inlines-hidden -O3 -DNDEBUG -DNDEBUG
C flags (Debug): -fsigned-char -W -Wall -Werror=return-type -Werror=non-virtual-dtor -Werror=address -Werror=sequence-point -Wformat -Werror=format-security -Wmissing-declarations -Wmissing-prototypes -Wstrict-prototypes -Wundef -Winit-self -Wpointer-arith -Wshadow -Wsign-promo -Wuninitialized -Wno-delete-non-virtual-dtor -Wno-unnamed-type-template-args -Wno-comment -fdiagnostics-show-option -Wno-long-long -Qunused-arguments -Wno-semicolon-before-method-body -ffunction-sections -fdata-sections -fvisibility=hidden -fvisibility-inlines-hidden -g -O0 -DDEBUG -D_DEBUG
Linker flags (Release): -Wl,-dead_strip
Linker flags (Debug): -Wl,-dead_strip
ccache: NO
Precompiled headers: NO
Extra dependencies: /Library/Developer/CommandLineTools/SDKs/MacOSX11.1.sdk/System/Library/Frameworks/OpenGL.framework
3rdparty dependencies:

OpenCV modules:
To be built: aruco bgsegm bioinspired calib3d ccalib core datasets dnn dnn_objdetect dpm face features2d flann fuzzy hfs highgui img_hash imgcodecs imgproc line_descriptor ml objdetect optflow phase_unwrapping photo plot python2 python3 reg rgbd saliency shape stereo stitching structured_light superres surface_matching text tracking ts video videoio videostab xfeatures2d ximgproc xobjdetect xphoto
Disabled: world
Disabled by dependency: -
Unavailable: cnn_3dobj cudaarithm cudabgsegm cudacodec cudafeatures2d cudafilters cudaimgproc cudalegacy cudaobjdetect cudaoptflow cudastereo cudawarping cudev cvv freetype hdf java matlab ovis sfm viz
Applications: tests perf_tests examples apps
Documentation: NO
Non-free algorithms: NO

GUI:
QT: YES (ver 5.15.2)
QT OpenGL support: YES (Qt5::OpenGL 5.15.2)
Cocoa: YES
OpenGL support: YES (/Library/Developer/CommandLineTools/SDKs/MacOSX11.1.sdk/System/Library/Frameworks/OpenGL.framework /Library/Developer/CommandLineTools/SDKs/MacOSX11.1.sdk/System/Library/Frameworks/OpenGL.framework)
VTK support: NO

Media I/O:
ZLib: build (ver 1.2.11)
JPEG: build-libjpeg-turbo (ver 2.0.6-62)
WEBP: build (ver encoder: 0x020f)
PNG: build (ver 1.6.37)
TIFF: build (ver 42 - 4.2.0)
JPEG 2000: build (ver 1.900.1)
OpenEXR: build (ver 2.3.0)
HDR: YES
SUNRASTER: YES
PXM: YES

Video I/O:
DC1394: NO
FFMPEG: NO
avcodec: NO
avformat: NO
avutil: NO
swscale: NO
avresample: NO
GStreamer: NO
AVFoundation: YES
libv4l/libv4l2: NO
v4l/v4l2: NO

Parallel framework: GCD

Trace: YES (with Intel ITT)

Other third-party libraries:
Intel IPP: 2020.0.0 Gold [2020.0.0]
at: /Users/myname/opencv/build/3rdparty/ippicv/ippicv_mac/icv
Intel IPP IW: sources (2020.0.0)
at: /Users/myname/opencv/build/3rdparty/ippicv/ippicv_mac/iw
Lapack: YES (/Library/Developer/CommandLineTools/SDKs/MacOSX11.1.sdk/System/Library/Frameworks/Accelerate.framework -lm -ldl)
Eigen: NO
Custom HAL: NO
Protobuf: build (3.5.1)

OpenCL: YES (no extra features)
Include path: NO
Link libraries: -framework OpenCL

Python 2:
Interpreter: /usr/bin/python2.7 (ver 2.7.16)
Libraries: /usr/lib/libpython2.7.dylib (ver 2.7.16)
numpy: /System/Library/Frameworks/Python.framework/Versions/2.7/Extras/lib/python/numpy/core/include (ver 1.8.0rc1)
install path: lib/python2.7/site-packages

Python 3:
Interpreter: /usr/local/bin/python3 (ver 3.9.4)
Libraries: /usr/local/Frameworks/Python.framework/Versions/3.9/lib/libpython3.9.dylib (ver 3.9.4)
numpy: /usr/local/lib/python3.9/site-packages/numpy/core/include (ver 1.20.2)
install path: ~/.virtualenvs/OpenCV-3.4.14-py3/lib/python3.9/site-packages

Python (for build): /usr/bin/python2.7

Java:
ant: NO
JNI: NO
Java wrappers: NO
Java tests: NO

Install to: /Users/myname/installation/OpenCV-3.4.14

berak · August 1, 2021, 6:38am

so, AVFoundation is the only usable video backend on your box, and it’s quite limited

tl;dr:

sorry, but you cannot query the video codec like that.

sjsu_alumna · August 1, 2021, 9:36pm

So in order to be able to use cv::CAP_PROP_FOURCC, I would need FFMPEG built, correct? And the way to do that is by adding the line
-D WITH_FFMPEG=ON \
when using CMake to build OpenCV, as shown in step 2 of Install OpenCV 3.4.4 on macOS | LearnOpenCV, correct?

crackwitz · August 1, 2021, 10:47pm

just use ffmpeg directly. look at documentation for ffprobe. it can show you all information on the container and on every contained audio/video/… stream.

if all you need is to find out the codecs in a video file, OpenCV is the wrong library for that.

“the fourcc” doesn’t exist for a video. it exists per stream, because a fourcc represents a choice of codec/bitstream. most videos have a video stream and an audio stream, which means you have two different types of bytestream.

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How do you identify the codec of a .mp4 video file in Xcode?

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