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• Cannot encode vp9 video with alpha to ivf container

  28 juillet 2022, par Jakob Košir

  I'm trying to convert a vp8/webm video with transparency to vp9 and ivf container. I can encode the video to vp9 into webm container with the following command which correctly produces a vp9 video with transparency :

  


  ffmpeg -c:v libvpx -i dancer1.webm -c:v libvpx-vp9 dancer_vp9.webm


  


  So basically forcing libvpx encoders instead of ffmpeg native ones to support alpha.

  


  However if I try to use ivf container instead of webm the resulting video does not have transparency :

  


  ffmpeg -c:v libvpx -i dancer1.webm -c:v libvpx-vp9 dancer_vp9.ivf


  


  Does not have transparency when played with VLC, when converting frames to PNG using ffmpeg (ffmpeg -c:v libvpx-vp9 -i dancer_vp9.ivf -vf "select=eq(n\,0)" frame.png) and when played in Chrome (using webcodecs API). Does ivf not support alpha channel somehow or am I doing something wrong ?

  


  I also tried copying the stream with alpha from webm container to ivf (ffmpeg -i dancer1_vp9.webm -c copy dancer1_vp9_copy.ivf) which produces the same result, no transparency.

  


  Curiously if I force or don't force libvpx decoder (which is required to support transparency, ffmpeg native one seems to just discard the alpha channel) when reading vp8/vp9 webm video it produces the same result when outputting to ivf container, while when outputting to webm container the resulting video has alpha when using libvpx decoder and not when using native ffmepg decoder.

  


  ffprobe output of created ivf file :

  


  ffprobe version 5.0.1 Copyright (c) 2007-2022 the FFmpeg developers
  built with Apple clang version 13.1.6 (clang-1316.0.21.2.5)
  configuration: --prefix=/opt/homebrew/Cellar/ffmpeg/5.0.1_3 --enable-shared --enable-pthreads --enable-version3 --cc=clang --host-cflags= --host-ldflags= --enable-ffplay --enable-gnutls --enable-gpl --enable-libaom --enable-libbluray --enable-libdav1d --enable-libmp3lame --enable-libopus --enable-librav1e --enable-librist --enable-librubberband --enable-libsnappy --enable-libsrt --enable-libtesseract --enable-libtheora --enable-libvidstab --enable-libvmaf --enable-libvorbis --enable-libvpx --enable-libwebp --enable-libx264 --enable-libx265 --enable-libxml2 --enable-libxvid --enable-lzma --enable-libfontconfig --enable-libfreetype --enable-frei0r --enable-libass --enable-libopencore-amrnb --enable-libopencore-amrwb --enable-libopenjpeg --enable-libspeex --enable-libsoxr --enable-libzmq --enable-libzimg --disable-libjack --disable-indev=jack --enable-videotoolbox --enable-neon
  libavutil      57. 17.100 / 57. 17.100
  libavcodec     59. 18.100 / 59. 18.100
  libavformat    59. 16.100 / 59. 16.100
  libavdevice    59.  4.100 / 59.  4.100
  libavfilter     8. 24.100 /  8. 24.100
  libswscale      6.  4.100 /  6.  4.100
  libswresample   4.  3.100 /  4.  3.100
  libpostproc    56.  3.100 / 56.  3.100
Input #0, ivf, from 'dancer_vp9.ivf':
  Duration: 00:01:02.87, start: 0.000000, bitrate: 249 kb/s
  Stream #0:0: Video: vp9 (Profile 0) (VP90 / 0x30395056), yuv420p(tv), 640x360, 30 tbr, 30 tbn


  


• FFMPEG - Get timestamp from hls stream while downloading

  31 juillet 2022, par Oytoch

  I need to download a stream, take 1 frames per seconds for image analyse.

  


  I use FFmpeg to take the frames with a pipe to my script.

  


  ffmpeg -i XX.m3u8 -vcodec mjpeg -f image2pipe -r 1 -s 1280*720 pipe:1


  


  For my analyse, I need the timestamp and in the HLS we have this data in the m3u8 file :

  


  #EXT-X-PROGRAM-DATE-TIME:2022-07-31T19:10:12.745Z
#EXTINF:2.000,live
XXXXX.ts
#EXT-X-PROGRAM-DATE-TIME:2022-07-31T19:10:14.745Z


  


  ffmpeg output also something like this

  


  frame=    1 fps=0.0 q=7.5 size=      59kB time=00:00:01.00 bitrate= 480.3kbits/s speed=  36x


  


  the problem is that we don't know which second we are downloading

  


  is there a solution to get this timestamp ?
Thanks

  


• FFmpeg avutil.lib unresolved external symbol

  2 août 2022, par Sere

  i'm trying to use FFmpeg with visual sudio 2022 .NET 6 through an MSVC project.
I followed this tutorial : https://www.youtube.com/watch?v=qMNr1Su-nR8&ab_channel=HakanSoyalp.
I mean I have configureg Include (.h) file, library (.lib) files and dynamic (.dll) file copied into bin folder.
If I call for example the avformat_alloc_context() method inside the avformat.lib all work rightly, if I call for example av_file_map(...) inside the avutil.lib the compiler give me an error :
LNK2019 unresolved external symbol "int __cdecl av_file_map ...
But the avutil.lib is linked !!!
The same happen if I call other methods inside avutil.lib module.

  


  Thanks for help...

  


  Code :

  


  extern "C"&#xA;{&#xA;    #include <libavformat></libavformat>avformat.h>&#xA;    #include <libavutil></libavutil>file.h> // av_file_map&#xA;}&#xA;&#xA;int ConvertJPEGtoNALs(int argc, char* argv[])&#xA;{&#xA;    AVFormatContext* fmt_ctx = NULL;&#xA;    AVIOContext* avio_ctx = NULL;&#xA;    uint8_t* buffer = NULL, * avio_ctx_buffer = NULL;&#xA;    size_t buffer_size, avio_ctx_buffer_size = 4096;&#xA;    char* input_filename = NULL;&#xA;    int ret = 0;&#xA;    struct buffer_data bd = { 0 };&#xA;    if (argc != 2) {&#xA;        fprintf(stderr, "usage: %s input_file\n"&#xA;            "API example program to show how to read from a custom buffer "&#xA;            "accessed through AVIOContext.\n", argv[0]);&#xA;        return 1;&#xA;    }&#xA;    input_filename = argv[1];&#xA;    /* register codecs and formats and other lavf/lavc components*/&#xA;    //av_register_all();    //!deprecated&#xA;    /* slurp file content into buffer */&#xA;    ret = av_file_map(input_filename, &amp;buffer, &amp;buffer_size, 0, NULL);&#xA;    /* fill opaque structure used by the AVIOContext read callback */&#xA;    bd.ptr = buffer;&#xA;    bd.size = buffer_size; ???&#xA;    if (!(fmt_ctx = avformat_alloc_context())) {&#xA;        ret = AVERROR(ENOMEM);&#xA;        goto end;&#xA;    }&#xA;    //... to be continue ...&#xA;}&#xA;