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• FFmpeg library is detecting pixel format of VP9 video stream not correctly

  6 avril 2023, par Pikachu

  I am using a C code to detect pixel format of VP9 video stream in a WebM container. FFmpeg version 6.0, full shared library build, downloaded from official website. Operating system is Windows 10. I feed the library with a VP9 video encoded with alpha channel, pixel format is YUVA420p. It detects pixel format as YUV420p.

  


  I have found a similar question on StackOverflow.com, Is there a way to force FFMPEG to decode a video stream with alpha from ​a WebM video encoded with libvpx-vp9 ?, but it does not actually help.

  


  When I override the decoder with a libvpx, it continues to detect the pixel format as YUV420p instead of YUVA420p.

  


  C code is following. Note that error handling in code is omitted here for StackOverflow question to be shorter.

  


  AVFormatContext *fmt_ctx = NULL;
int err = avformat_open_input(&fmt_ctx, infp, NULL, NULL);
err = avformat_find_stream_info(fmt_ctx, NULL);
int stream = av_find_best_stream(fmt_ctx, AVMEDIA_TYPE_VIDEO, -1, -1, NULL, 0);
AVCodecParameters *codecpar = fmt_ctx->streams[stream]->codecpar;

const AVCodec *codec = NULL;
if (codecpar->codec_id == AV_CODEC_ID_VP9) {
    codec = avcodec_find_decoder_by_name(CODEC_LIBVPX_VP9);
} else {
    codec = avcodec_find_decoder(codecpar->codec_id);
}

AVCodecContext *ctx = avcodec_alloc_context3(codec);
err = avcodec_parameters_to_context(ctx, codecpar);
av_log(NULL, AV_LOG_DEBUG, "Pixel format: %d.\n", ctx->pix_fmt); //TODO:DEBUG.
err = avcodec_open2(ctx, codec, NULL);


  


  The program tells Pixel format: 0., which means AV_PIX_FMT_YUV420P, not the AV_PIX_FMT_YUVA420P !

  


  If I override pixel format manually, I am able to decode video with alpha channel and to see the transparent background, but it breaks the logics, because when a real YUV420p pixel format comes in and gets overridden by YUVA420p, this will be a problem.

  


  if (codecpar->codec_id == AV_CODEC_ID_VP9) {
    if (strcmp(codec->name, CODEC_LIBVPX_VP9) == 0) {
        if (ctx->pix_fmt == AV_PIX_FMT_YUV420P) {
            ctx->pix_fmt = AV_PIX_FMT_YUVA420P;
        }
    }
}


  


  At the same time ffmpeg tool started from command line with libvpx decoder tells that my video has YUVA420p pixel format. Output is following.

  


  D:\Temp\4>ffmpeg -c:v libvpx-vp9 -i yuva.webm
ffmpeg version 6.0-full_build-www.gyan.dev Copyright (c) 2000-2023 the FFmpeg developers
  built with gcc 12.2.0 (Rev10, Built by MSYS2 project)
  configuration: --enable-gpl --enable-version3 --enable-shared --disable-w32threads --disable-autodetect --enable-fontconfig --enable-iconv --enable-gnutls --enable-libxml2 --enable-gmp --enable-bzlib --enable-lzma --enable-libsnappy --enable-zlib --enable-librist --enable-libsrt --enable-libssh --enable-libzmq --enable-avisynth --enable-libbluray --enable-libcaca --enable-sdl2 --enable-libaribb24 --enable-libdav1d --enable-libdavs2 --enable-libuavs3d --enable-libzvbi --enable-librav1e --enable-libsvtav1 --enable-libwebp --enable-libx264 --enable-libx265 --enable-libxavs2 --enable-libxvid --enable-libaom --enable-libjxl --enable-libopenjpeg --enable-libvpx --enable-mediafoundation --enable-libass --enable-frei0r --enable-libfreetype --enable-libfribidi --enable-liblensfun --enable-libvidstab --enable-libvmaf --enable-libzimg --enable-amf --enable-cuda-llvm --enable-cuvid --enable-ffnvcodec --enable-nvdec --enable-nvenc --enable-d3d11va --enable-dxva2 --enable-libvpl --enable-libshaderc --enable-vulkan --enable-libplacebo --enable-opencl --enable-libcdio --enable-libgme --enable-libmodplug --enable-libopenmpt --enable-libopencore-amrwb --enable-libmp3lame --enable-libshine --enable-libtheora --enable-libtwolame --enable-libvo-amrwbenc --enable-libilbc --enable-libgsm --enable-libopencore-amrnb --enable-libopus --enable-libspeex --enable-libvorbis --enable-ladspa --enable-libbs2b --enable-libflite --enable-libmysofa --enable-librubberband --enable-libsoxr --enable-chromaprint
  libavutil      58.  2.100 / 58.  2.100
  libavcodec     60.  3.100 / 60.  3.100
  libavformat    60.  3.100 / 60.  3.100
  libavdevice    60.  1.100 / 60.  1.100
  libavfilter     9.  3.100 /  9.  3.100
  libswscale      7.  1.100 /  7.  1.100
  libswresample   4. 10.100 /  4. 10.100
  libpostproc    57.  1.100 / 57.  1.100
[libvpx-vp9 @ 000001ecdf6002c0] v1.13.0-71-g45dc0d34d
    Last message repeated 1 times
Input #0, matroska,webm, from 'yuva.webm':
  Metadata:
    ENCODER         : Lavf60.3.100
  Duration: 00:00:05.55, start: 0.000000, bitrate: 227 kb/s
  Stream #0:0: Video: vp9 (Profile 0), yuva420p(tv, progressive), 1920x1080, SAR 1:1 DAR 16:9, 60 fps, 60 tbr, 1k tbn
    Metadata:
      alpha_mode      : 1
      ENCODER         : Lavc60.3.100 libvpx-vp9
      DURATION        : 00:00:05.550000000
At least one output file must be specified


  


  Here is my YUVA420p in the first video stream at the end of the console output :

  


  Stream #0:0: Video: vp9 (Profile 0), yuva420p(tv, progressive), 1920x1080, SAR 1:1 DAR 16:9, 60 fps, 60 tbr, 1k tbn


  


  


  The questions are following.

  


  

  1. How to detect real pixel format of VP9 video with FFmpeg library in C code reliably ?

  


  2. Why is the C code not detecting the actual pixel format even with codec overriden to libvpx ?

  


  


  Thank you.

  


• PyDub : ffmpeg header missing

  7 février 2024, par Ray Siplao

  I made a simple Python program that add short pauses at the start of mp3 files

  


  import os

from pydub import AudioSegment

AUDIO_DIR = 'C:\\Users\\Ray\\Downloads\\sentence-audio'
OUT_DIR = 'C:\\Users\\Ray\\Downloads\\out-audio'

pause = AudioSegment.silent(duration=400)

for fname in os.listdir(AUDIO_DIR):
    print(f'Processing {fname}')
    newf = os.path.join(OUT_DIR, os.path.basename(fname))
    if os.path.isfile(newf):
        print(f'{fname} exists')
        continue
    audio = AudioSegment.from_mp3(os.path.join(AUDIO_DIR, fname))
    new = pause + audio
    new.export(newf, format='mp3')
    print(f'{fname} lengthened')


  


  While running this program, I received the below error message for a particular mp3 file

  


  Traceback (most recent call last):&#xA;  File "C:\Users\Ray\Downloads\lengthen.py", line 16, in <module>&#xA;    audio = AudioSegment.from_mp3(os.path.join(AUDIO_DIR, fname))&#xA;  File "C:\Python39\lib\site-packages\pydub\audio_segment.py", line 796, in from_mp3&#xA;    return cls.from_file(file, &#x27;mp3&#x27;, parameters=parameters)&#xA;  File "C:\Python39\lib\site-packages\pydub\audio_segment.py", line 773, in from_file&#xA;    raise CouldntDecodeError(&#xA;pydub.exceptions.CouldntDecodeError: Decoding failed. ffmpeg returned error code: 1&#xA;&#xA;Output from ffmpeg/avlib:&#xA;&#xA;ffmpeg version git-2020-04-03-52523b6 Copyright (c) 2000-2020 the FFmpeg developers&#xA;  built with gcc 9.3.1 (GCC) 20200328&#xA;  configuration: --enable-gpl --enable-version3 --enable-sdl2 --enable-fontconfig --enable-gnutls --enable-iconv --enable-libass --enable-libdav1d --enable-libbluray --enable-libfreetype --enable-libmp3lame --enable-libopencore-amrnb --enable-libopencore-amrwb --enable-libopenjpeg --enable-libopus --enable-libshine --enable-libsnappy --enable-libsoxr --enable-libsrt --enable-libtheora --enable-libtwolame --enable-libvpx --enable-libwavpack --enable-libwebp --enable-libx264 --enable-libx265 --enable-libxml2 --enable-libzimg --enable-lzma --enable-zlib --enable-gmp --enable-libvidstab --enable-libvmaf --enable-libvorbis --enable-libvo-amrwbenc --enable-libmysofa --enable-libspeex --enable-libxvid --enable-libaom --enable-libmfx --enable-ffnvcodec --enable-cuda-llvm --enable-cuvid --enable-d3d11va --enable-nvenc --enable-nvdec --enable-dxva2 --enable-avisynth --enable-libopenmpt --enable-amf&#xA;  libavutil      56. 42.102 / 56. 42.102&#xA;  libavcodec     58. 77.101 / 58. 77.101&#xA;  libavformat    58. 42.100 / 58. 42.100&#xA;  libavdevice    58.  9.103 / 58.  9.103&#xA;  libavfilter     7. 77.101 /  7. 77.101&#xA;  libswscale      5.  6.101 /  5.  6.101&#xA;  libswresample   3.  6.100 /  3.  6.100&#xA;  libpostproc    55.  6.100 / 55.  6.100&#xA;[mp3float @ 0000016489995380] Header missing&#xA;    Last message repeated 71 times&#xA;[mp3 @ 000001648998b500] decoding for stream 0 failed&#xA;[mp3 @ 000001648998b500] Could not find codec parameters for stream 0 (Audio: mp3 (mp3float), 0 channels, fltp): unspecified frame size&#xA;Consider increasing the value for the &#x27;analyzeduration&#x27; and &#x27;probesize&#x27; options&#xA;Input #0, mp3, from &#x27;C:\Users\Ray\Downloads\sentence-audio\354.mp3&#x27;:&#xA;  Duration: N/A, start: 0.000000, bitrate: N/A&#xA;    Stream #0:0: Audio: mp3, 0 channels, fltp&#xA;Stream mapping:&#xA;  Stream #0:0 -> #0:0 (mp3 (mp3float) -> pcm_s16le (native))&#xA;Press [q] to stop, [?] for help&#xA;[mp3float @ 0000016489995800] Header missing&#xA;Error while decoding stream #0:0: Invalid data found when processing input&#xA;[mp3float @ 0000016489995800] Header missing&#xA;Error while decoding stream #0:0: Invalid data found when processing input&#xA;[mp3float @ 0000016489995800] Header missing&#xA;Error while decoding stream #0:0: Invalid data found when processing input&#xA;[mp3float @ 0000016489995800] Header missing&#xA;Error while decoding stream #0:0: Invalid data found when processing input&#xA;[mp3float @ 0000016489995800] Header missing&#xA;Error while decoding stream #0:0: Invalid data found when processing input&#xA;[mp3float @ 0000016489995800] Header missing&#xA;Error while decoding stream #0:0: Invalid data found when processing input&#xA;[mp3float @ 0000016489995800] Header missing&#xA;Error while decoding stream #0:0: Invalid data found when processing input&#xA;[mp3float @ 0000016489995800] Header missing&#xA;Error while decoding stream #0:0: Invalid data found when processing input&#xA;[mp3float @ 0000016489995800] Header missing&#xA;Error while decoding stream #0:0: Invalid data found when processing input&#xA;[mp3float @ 0000016489995800] Header missing&#xA;Error while decoding stream #0:0: Invalid data found when processing input&#xA;[mp3float @ 0000016489995800] Header missing&#xA;Error while decoding stream #0:0: Invalid data found when processing input&#xA;[mp3float @ 0000016489995800] Header missing&#xA;Error while decoding stream #0:0: Invalid data found when processing input&#xA;[mp3float @ 0000016489995800] Header missing&#xA;Error while decoding stream #0:0: Invalid data found when processing input&#xA;[mp3float @ 0000016489995800] Header missing&#xA;Error while decoding stream #0:0: Invalid data found when processing input&#xA;[mp3float @ 0000016489995800] Header missing&#xA;Error while decoding stream #0:0: Invalid data found when processing input&#xA;[mp3float @ 0000016489995800] Header missing&#xA;Error while decoding stream #0:0: Invalid data found when processing input&#xA;[mp3float @ 0000016489995800] Header missing&#xA;Error while decoding stream #0:0: Invalid data found when processing input&#xA;...&#xA;</module>

  


  I thought at first that the mp3 file is corrupt, thus it is unplayable. But, when I played the file in a media player, it was fine.

  


  I don't know how to resolve this issue. Is there any workarounds ?

  


• How do I install ffmpeg on one EC2 Amazon Linux instance that can stream a mp4 ? [closed]

  12 septembre 2020, par starpebble

  Good day. How can I install ffmpeg on an EC2 amazon linux machine that can stream a mp4 ?

  


  The goal : an ffmpeg install on EC2 Amazon Linux that can stream one mp4 to one rtmps endpoint. Then, create an integration test suite with it.

  


  Is it just me or is ffmpeg a little crippled on EC2 Amazon Linux ?

  


  Example :

  


  ffmpeg -re -i input.mp4 -c:v libx264 -b:v 6000K -maxrate 6000K -pix_fmt yuv420p -s 1920x1080 -profile:v main -preset veryfast -g 120 -x264opts "nal-hrd=cbr:no-scenecut” -acodec aac -ab 160k -ar 44100 -f flv rtmps:///app/


  


  Linux OS :

  


  Linux version 4.14.193-113.317.amzn1.x86_64 (mockbuild@koji-pdx-corp-builder-60005) (gcc version 7.2.1 20170915 (Red Hat 7.2.1-2) (GCC)) #1 SMP Thu Sep 3 19:08:08 UTC 2020


  


  The stackoverflow answer to similar questions fail to install a ffmpeg that can stream.

  


  An installation script such as Install FFMPEG Library on EC2 Server fail this year.

  


  The static downloads referenced on John Van Sickle-FFmpeg Static Builds fail to stream to IVS. I tried the i686 release, my first guess for an x86_64 instance.

  


  The git source tree compiled binary fails to stream. Example : The tip of the tree isn't what I expected because the binary fails to recognize switches like -preset.

  


  I'd love to be able to explain streaming to anyone. Thanks.