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• avutil/imgutils : Add wrapper for av_image_copy() to avoid casts

  6 septembre 2023, par Andreas Rheinhardt

  avutil/imgutils : Add wrapper for av_image_copy() to avoid casts
  av_image_copy() accepts const uint8_t* const * as source ;
  
  lots of user have uint8_t* const * and therefore either
  
  cast (the majority) or copy the array of pointers.
  This commit changes this by adding a static inline wrapper
  
  for av_image_copy() that casts between the two types
  
  so that we do not need to add casts everywhere else.
  Signed-off-by : Andreas Rheinhardt <andreas.rheinhardt@outlook.com>
  

  • [DH] doc/APIchanges
  • [DH] doc/examples/demux_decode.c
  • [DH] libavcodec/amfenc.c
  • [DH] libavcodec/libkvazaar.c
  • [DH] libavcodec/libopenh264dec.c
  • [DH] libavcodec/libvpxdec.c
  • [DH] libavcodec/mediacodecenc.c
  • [DH] libavcodec/mmaldec.c
  • [DH] libavcodec/nuv.c
  • [DH] libavcodec/nvenc.c
  • [DH] libavcodec/omx.c
  • [DH] libavcodec/v210dec.c
  • [DH] libavdevice/xv.c
  • [DH] libavfilter/lavfutils.c
  • [DH] libavfilter/vf_framepack.c
  • [DH] libavfilter/vf_pullup.c
  • [DH] libavfilter/yadif_common.c
  • [DH] libavutil/frame.c
  • [DH] libavutil/hwcontext_d3d11va.c
  • [DH] libavutil/hwcontext_dxva2.c
  • [DH] libavutil/imgutils.h
  • [DH] libavutil/version.h

• Compiling FFmpeg with Libass using MSVC

  2 avril 2019, par maxhap

  First a bit of background.

  I’m trying to compile ffmpeg on windows with the libass extensions/configuration option.

  Using the visual studio project libass-msvc I built libass using Visual Studio as a static lib.

  I then installed MinGW with MSYS and pkg-config. Following the instructions on the ffmpeg MSVC installation guide I configured the environment to build with the MSVC linker and to build in x64.

  When I try to configure libass for compilation using ./configure —enable-libass —toolchain=msvc I get the following error in the log file :

  File not found ass/ass.h

  pkg-config can not find libass

  I have tried the following to fix this.

  1. Create a .pc file for libass and add this to the PKG_CONFIG_PATH environment variable. See file content below. (After doing this pkg-config libass —version prints 0.81, not the right version number but at least something.)

  2. Copy libass .h files into a MinGW/include/ass folder and the .lib file into the MinGW/libs folder.

  3. Add libass include and bin folders to PATH environment variable

  4. Download libass and dependencies source then try to build it using MSYS with MSVC compiler. My aim here was to be able to use "make install" and let MinGW install libass to the correct locations. After hours of trying to fix linker errors, I abandoned this idea as some of the libass dependencies make files only work with the GCC GNU compiler.

  5. Compile libass with GCC GNU using MinGW make/make install then try and install libass using the GNU libs. Again this led to linker errors (I know this was a bad idea but was worth a try).

  6. Tried using extra lib and include build configuration options —extra-cflags="ffmpeg-dir/extra/include" \
     — extra-ldflags="ffmped-dir/extra/ffmpeg_build/lib" then adding the libs and .h files into those locations

  .pc file

  libass.pc:
  
  prefix=/MinGW
  
  includedir=libass-directory/include
  
  libdir=libass-director/x64/bin/
  
  
  
  Name: libass
  
  Description: Libass project
  
  Version: 0.13.7

  I am now completely stuck and out of ideas if anyone could give any insight or suggestions into what I’m doing wrong that would be fantastic.

  Update

  I created INCLUDE and LIBDIR environment path variable containing the libass paths. Which now correctly includes libass. However, I now get the following linker error for the function check_ass_library_init.

  check_func_headers ass/ass.h ass_library_init
  check_ld cc
  check_cc
  BEGIN ./ffconf.RZMYFWdc/test.c
  1 #include
  2 #include
  3 long check_ass_library_init(void) return (long)
  ass_library_init ;
  4 int main(void) int ret = 0 ;
  5 ret |= ((intptr_t)check_ass_library_init) & 0xFFFF ;
  6 return ret ;
  END ./ffconf.RZMYFWdc/test.c
  cl -D_ISOC99_SOURCE -D_FILE_OFFSET_BITS=64 -D_LARGEFILE_SOURCE -
  D_USE_MATH_DEFINES -D_CRT_SECURE_NO_WARNINGS -D_CRT_NONSTDC_NO_WARNINGS -
  D_WIN32_WINNT=0x0502 -nologo -c -Fo./ffconf.RZMYFWdc/test.o
  ./ffconf.RZMYFWdc/test.c
  test.c
  ./ffconf.RZMYFWdc/test.c(3) : warning C4311 : ’type cast’ : pointer truncation
  from ’ASS_Library *(__cdecl *)(void)’ to ’long’
  ./compat/windows/mslink -nologo -out :./ffconf.RZMYFWdc/test.exe
  ./ffconf.RZMYFWdc/test.o psapi.lib advapi32.lib shell32.lib ole32.lib
  test.o : error LNK2019 : unresolved external symbol ass_library_init
  referenced in function check_ass_library_init
  ./ffconf.RZMYFWdc/test.exe : fatal error LNK1120 : 1 unresolved externals
  ERROR : libass not found using pkg-config

  The libass test project which uses ass_library_init compiles fine using the same lib files, the libs appear to be fine.

  From what I see from this line "./compat/windows/mslink -nologo -out:./ffconf.RZMYFWdc/test.exe ./ffconf.RZMYFWdc/test.o psapi.lib advapi32.lib shell32.lib ole32.lib" libass is not being passed to the linker.
  I suspect that the configuration file is not creating the link to libass in the make file when compiling with MSVC.

  Am I correct or am I going about compiling this in the wrong way ?

• How do I write to a file in Golang using a pointer to the C data ?

  20 juillet 2020, par nevernew

  I'm writing an app for the windows platform using FFmpeg and it's golang wrapper goav, but I'm having trouble understanding how to use the C pointers to gain access to an array.

  



  I'm trying to write the frame data, pointed to by a uint8 pointer from C, to a .ppm file in golang.

  



  Once I have this done, for proof of concept that FFmpeg is doing what I expect it to, I want to set the frames to a texture in OpenGl to make a video player with cool transitions ; any pointers to do that nice and efficiently would be so very helpful ! I'm guessing I need to write some shader code to draw the ppm as a texture...

  



  The PPM file structure looks pretty simple just the header and then a byte of data for each red, green and blue value of each pixel in the frame from top left to bottom right

  



  I'm starting to understanding how to cast the pointers between C and Go types, but how can I access the data and write it in Go with the same result as C ? In C I just have to set the pointer offset for the data and state how much of it to write :

  



  for (y = 0; y < height; y++) {
    fwrite(pFrame->data[0]+y*pFrame->linesize[0], 1, width*3, pFile);
}


  



  I've stripped out all the relevant parts of the C code, the wrapper and my code, shown below :

  



  C code - libavutil/frame.h

  



  #include 

typedef struct AVFrame {
#define AV_NUM_DATA_POINTERS 8
    uint8_t *data[AV_NUM_DATA_POINTERS];
    int linesize[AV_NUM_DATA_POINTERS];
}


  



  Golang goav wrapper

  



  package avutil&#xA;&#xA;/*&#xA;    #cgo pkg-config: libavutil&#xA;    #include <libavutil></libavutil>frame.h>&#xA;    #include &#xA;*/&#xA;import "C"&#xA;import (&#xA;    "unsafe"&#xA;)&#xA;&#xA;type Frame C.struct_AVFrame&#xA;&#xA;func Data(f *Frame) *uint8 {&#xA;    return (*uint8)(unsafe.Pointer((*C.uint8_t)(unsafe.Pointer(&amp;f.data))))&#xA;}&#xA;func Linesize(f *Frame) int {&#xA;    return int(*(*C.int)(unsafe.Pointer(&amp;f.linesize)))&#xA;}&#xA;

  



  My Golang code

  



  package main

import "github.com/giorgisio/goav/avutil"

func saveFrame(videoFrame *avutil.Frame, width int, height int, iFrame int) {
    var szFilename string
    var y int
    var file *os.File
    var err error

    szFilename = ""

    // Open file
    szFilename = fmt.Sprintf("frame%d.ppm", iFrame)

    if file, err = os.Create(szFilename); err != nil {
        log.Println("Error Reading")
    }

    // Write header
    fh := []byte(fmt.Sprintf("P6\n%d %d\n255\n", width, height))
    file.Write(fh)
    var b byte = 0
    // Write pixel data
    for y = 0; y < height; y++ {
        d := avutil.Data(videoFrame) // d should be a pointer to the first byte of data
        l := avutil.Linesize(videoFrame)

        // I'm basically lost trying to figure out how to correctly write
        // this to a file, the file is created, but when I open it in GIMP
        // the image is mostly black with glitchy fuzz - so it's not being
        // written properly; the header seems to be ok, it knows the height
        // and width at least.

        data := make([]byte, l*3)

        ptr := unsafe.Pointer(d)
        for i := 0; i < l; i++ {
            datum := (*uint8)(unsafe.Pointer(uintptr(ptr) + (uintptr(i)+(uintptr(y)*uintptr(l)))*unsafe.Sizeof(*d)))
            data = append(data, *datum)
            //fmt.Println(*datum)
        }

        n, err := file.Write(data)
        if err != nil {
            log.Println("Error Writing:", szFilename, "-", n)
        }
    }

    file.Close()
}


  



  So, how can I write to a file using a pointer to the data, like you can do in C, and get the same result ?

  



  The first frame should be black so all 0's but I'm getting a glitchy fuzz, so it must be accessing some random data

  



  Update : My fix using a C function to save :

  



  package avutil&#xA;&#xA;/*&#xA;    #cgo pkg-config: libavutil&#xA;    #include <libavutil></libavutil>frame.h>&#xA;    #include &#xA;    #include &#xA;&#xA;    void SaveFrame(const char* location, AVFrame *pFrame, int width, int height) {&#xA;        FILE *pFile;&#xA;        int  y;&#xA;&#xA;        // Open file&#xA;        pFile=fopen(location, "wb");&#xA;        if(pFile==NULL)&#xA;            return;&#xA;&#xA;        // Write header&#xA;        fprintf(pFile, "P6\n%d %d\n255\n", width, height);&#xA;&#xA;        // Write pixel data&#xA;        for(y=0; ydata[0]&#x2B;y*pFrame->linesize[0], 1, width*3, pFile);&#xA;&#xA;        // Close file&#xA;        fclose(pFile);&#xA;    }&#xA;    uint8_t* GetData(AVFrame *pFrame) {&#xA;        return pFrame->data[0];&#xA;    }&#xA;*/&#xA;import "C"&#xA;

  



  I updated the avutil file, in the goav wrapper package, with this save function at the top, then pass it the frame context so it can get the data pointer from it. I also added this Go function to that avutil file to call the C function

  



  func SaveFrame(location string, f *Frame, width int, height int) {
    csLoc := C.CString(location)
    C.SaveFrame(csLoc, (*C.struct_AVFrame)(unsafe.Pointer(f)), C.int(width), C.int(height))
    C.free(unsafe.Pointer(csLoc))
}