Sur d’autres sites (7756)

• How to read alpha channel from .webm video using ffmpeg in c++

  27 octobre 2022, par Pasin Kunamart

  Background

  


  I have a .webm file (pix_fmt : yuva420p) converted from .mov video file in order to reduce file size and I would like to read the video data using c++, so I followed using this repo as a reference.

  


  This works perfectly on .mov video.

  


  Problem

  


  By using same repo, however, there is no alpha channel data (pure zeros on that channel) for .webm video but I can get the alpha data from .mov video.

  


  Apparently many people already noticed that after the video conversion, ffmpeg somehow detect video as yuv420p + alpha_mode : 1 and thus alpha channel is not used but there is no one discuss about workaround of this.

  


  I tried forcing pixel format during this part to use yuva420p but that just broke the whole program.

  


    // Set up sws scaler
    if (!sws_scaler_ctx) {
        auto source_pix_fmt = correct_for_deprecated_pixel_format(av_codec_ctx->pix_fmt);
        sws_scaler_ctx = sws_getContext(width, height, source_pix_fmt,
                                        width, height, AV_PIX_FMT_RGB0,
                                        SWS_BILINEAR, NULL, NULL, NULL);
    }


  


  I also verified my video that it contains alpha channel using other source so I am sure there is alpha channel in my webm video but I cannot fetch the data using ffmpeg.

  


  Is there a way to fetch the alpha data ? Other video format or using other libraries work as well as long as it does have some file compression but I need to access the data in c++.

  


  Note : This is the code I used for converting video to webm

  


  ffmpeg -i input.mov -c:v libvpx-vp9 -pix_fmt yuva420p output.webm


  


• Grayscale streaming from raw video using FFMPEG

  31 août 2022, par user1657208

  I have a raw video file (testvideo_1000f.raw) that I am trying to stream in gray scale using ffmpeg and output the grayscale video to output.swf. The command I am using to do this is :

  



  ffmpeg/ffmpeg -qmin 2 -qmax 31 -s 320x240 -f rawvideo -flags gray -pix_fmt:output gray -an -i testvideo_1000f.raw output.swf


  



  However, the result from this command is a video stream that is in gray scale but still contains some of the chrominance data. The output from this command is pasted below :

  



      3 [volta]/home/student/elliott> ffmpeg/ffmpeg -qmin 2 -qmax 31 -s 320x240 -f rawvideo -flags gray -pix_fmt:output gray -an -i testvideo_1000f.raw output.swf
ffmpeg version N-41632-g2b1fc56 Copyright (c) 2000-2012 the FFmpeg developers
  built on Jul 29 2012 10:27:26 with gcc 4.1.2 20080704 (Red Hat 4.1.2-51)
  configuration: 
  libavutil      51. 58.100 / 51. 58.100
  libavcodec     54. 25.100 / 54. 25.100
  libavformat    54.  6.101 / 54.  6.101
  libavdevice    54.  0.100 / 54.  0.100
  libavfilter     2. 80.100 /  2. 80.100
  libswscale      2.  1.100 /  2.  1.100
  libswresample   0. 15.100 /  0. 15.100
*** CHOOSING 8
[rawvideo @ 0xdda9660] Estimating duration from bitrate, this may be inaccurate
Input #0, rawvideo, from 'testvideo_1000f.raw':
  Duration: N/A, start: 0.000000, bitrate: N/A
   Stream #0:0: Video: rawvideo (Y800 / 0x30303859), gray, 320x240, 25 tbr, 25 tbn, 25 tbc
File 'output.swf' already exists. Overwrite ? [y/N] y
w:320 h:240 pixfmt:gray tb:1/25 fr:25/1 sar:0/1 sws_param:flags=2
[ffmpeg_buffersink @ 0xddb7b40] No opaque field provided
[format @ 0xddb7d40] auto-inserting filter 'auto-inserted scaler 0' between the filter 'Parsed_null_0' and the filter 'format'
[auto-inserted scaler 0 @ 0xddb7920] w:320 h:240 fmt:gray sar:0/1 -> w:320 h:240 fmt:yuv420p sar:0/1 flags:0x4
*** CHOOSING 8
Output #0, swf, to 'output.swf':
  Metadata:
    encoder         : Lavf54.6.101
   Stream #0:0: Video: flv1, yuv420p, 320x240, q=2-31, 200 kb/s, 90k tbn, 25 tbc
Stream mapping:
  Stream #0:0 -> #0:0 (rawvideo -> flv)
Press [q] to stop, [?] for help
Truncating packet of size 76800 to 1 2875kB time=00:00:40.84 bitrate= 576.7kbits/s    
frame= 1500 fps=1035 q=24.8 Lsize=    4194kB time=00:01:00.00 bitrate= 572.6kbits/s    
video:4166kB audio:0kB global headers:0kB muxing overhead 0.669245%


  



  I am fairly new to FFMPEG and I am afraid I am using either the wrong syntax or the wrong parameters in my command line. For some reason, the format of the output is yuv420p. I have tried searching for this answer all over but have had no luck. Could anyone please help me and tell me why the output is being formatted in yuv420p when I am giving the command for it to be in 8bit grayscale ? Any help would be greatly appreciated. Thank you.

  



  Marc Elliott

  


• FFMpeg C++ encoder fails with hardware acceleration quick sync intel

  28 août 2022, par teals

  I am trying to debug an issue I have with a simple C++ encoder using FFMmpeg. The following code below works correctly on these other hardware acceleration systems/platforms :

  


  

  • Mac/VideoToolbox,

  


  • Cuda/NVEnc

  


  • Raspberry pi/h264_v4l2m2m.

  


  


  It fails on intel quick sync at avcodec_open2. I'm using Ubuntu 22.04. I built FFMpeg from source with the Intel Media SDK installed and configured. I verified that the QuickSync install works. I also have a corresponding decoder implementation that works correctly using intel quick sync. So I know everything properly installed. I am also running this on an 11th Gen Intel CPU.

  


  [hevc_qsv @ 0x564b0d34f0c0] Low power mode is unsupported (This sometimes shows up)
[hevc_qsv @ 0x563691234000] some encoding parameters are not supported by the QSV runtime. Please double check the input parameters.
Error initializing output stream 0:0 -- Error while opening encoder for output stream #0:0 - maybe incorrect parameters such as bit_rate, rate, width or height


  


  This is the only error that I get and I haven't found any helpful resources. I tried playing around with different parameters but nothing seems to work. Any help or insight would be extremely helpful.

  


  bool VideoEncoder::create() {&#xA;    char const* outfile = filePath.c_str();&#xA;&#xA;     // open output format context&#xA;    int ret = avformat_alloc_output_context2(&amp;ofctx, nullptr, nullptr, outfile);&#xA;    if (ret &lt; 0) {&#xA;        std::cerr &lt;&lt; "fail to avformat_alloc_output_context2(" &lt;&lt; outfile &lt;&lt; "): ret=" &lt;&lt; ret;&#xA;        return false;&#xA;    }&#xA;&#xA;    // create new video stream&#xA;    const AVCodec* codec = avcodec_find_encoder_by_name(encoderName.c_str());&#xA;    vstrm = avformat_new_stream(ofctx, codec);&#xA;    if (!vstrm) {&#xA;        std::cerr &lt;&lt; "fail to avformat_new_stream";&#xA;        return false;&#xA;    }&#xA;&#xA;    // open video encoder&#xA;    cctx = avcodec_alloc_context3(codec);&#xA;    if (!vstrm) {&#xA;        std::cerr &lt;&lt; "fail to avcodec_alloc_context3";&#xA;        return false;&#xA;    }&#xA;    const AVRational dst_fps = {fps, 1};&#xA;    cctx->width = width;&#xA;    cctx->height = height;&#xA;    if(pixel_format != AV_PIX_FMT_NONE) {&#xA;        cctx->pix_fmt = pixel_format;&#xA;    }&#xA;    else {&#xA;        cctx->pix_fmt = codec->pix_fmts[0];&#xA;    }&#xA;    cctx->time_base = av_inv_q(dst_fps);&#xA;    cctx->framerate = dst_fps;&#xA;    cctx->bit_rate = bitrate * 1000000;&#xA;&#xA;&#xA;    AVDictionary* options = nullptr;&#xA;    if(gpu_id >= 0) {&#xA;        av_dict_set_int(&amp;options, "gpu", gpu_id, 0);&#xA;    }&#xA;&#xA;    &#xA;    if (ofctx->oformat->flags &amp; AVFMT_GLOBALHEADER)&#xA;        cctx->flags |= AV_CODEC_FLAG_GLOBAL_HEADER;&#xA;    ret = avcodec_open2(cctx, codec, &amp;options);&#xA;    if (ret &lt; 0) {&#xA;        std::cerr &lt;&lt; "fail to avcodec_open2: ret=" &lt;&lt; ret;&#xA;        return false;&#xA;    }&#xA;    avcodec_parameters_from_context(vstrm->codecpar, cctx);&#xA;&#xA;    //For mac/quicktime we need to add hvc1 tag.&#xA;    if (encoderName.find("hevc") != std::string::npos) {&#xA;        vstrm->codecpar->codec_tag = MKTAG(&#x27;h&#x27;, &#x27;v&#x27;, &#x27;c&#x27;, &#x27;1&#x27;);&#xA;    }&#xA;&#xA;    /*&#xA;    std::cout&#xA;        &lt;&lt; "outfile: " &lt;&lt; outfile &lt;&lt; "\n"&#xA;        &lt;&lt; "format:  " &lt;&lt; ofctx->oformat->name &lt;&lt; "\n"&#xA;        &lt;&lt; "vcodec:  " &lt;&lt; codec->name &lt;&lt; "\n"&#xA;        &lt;&lt; "size:    " &lt;&lt; width &lt;&lt; &#x27;x&#x27; &lt;&lt; height &lt;&lt; "\n"&#xA;        &lt;&lt; "fps:     " &lt;&lt; av_q2d(cctx->framerate) &lt;&lt; "\n"&#xA;        &lt;&lt; "pixfmt:  " &lt;&lt; av_get_pix_fmt_name(cctx->pix_fmt) &lt;&lt; "\n"&#xA;        &lt;&lt; std::flush;*/&#xA;&#xA;    // initialize sample scaler&#xA;    swsCtx = sws_getContext(&#xA;        width, height, AV_PIX_FMT_BGR24,&#xA;        width, height, cctx->pix_fmt,&#xA;        SWS_BILINEAR, nullptr, nullptr, nullptr);&#xA;    if (!swsCtx) {&#xA;        std::cerr &lt;&lt; "fail to sws_getContext";&#xA;        return false;&#xA;    }&#xA;&#xA;    // allocate frame buffer for encoding&#xA;    frame = av_frame_alloc();&#xA;    frame->width = width;&#xA;    frame->height = height;&#xA;    frame->format = static_cast<int>(cctx->pix_fmt);&#xA;    ret = av_frame_get_buffer(frame, 32);&#xA;    if (ret &lt; 0) {&#xA;        std::cerr &lt;&lt; "fail to av_frame_get_buffer: ret=" &lt;&lt; ret;&#xA;        return false;&#xA;    }&#xA;&#xA;    // allocate packet to retrive encoded frame&#xA;    pkt = av_packet_alloc();&#xA;    // open output IO context&#xA;    ret = avio_open2(&amp;ofctx->pb, outfile, AVIO_FLAG_WRITE, nullptr, nullptr);&#xA;    if (ret &lt; 0) {&#xA;        std::cerr &lt;&lt; "fail to avio_open2: ret=" &lt;&lt; ret;&#xA;        return false;&#xA;    }&#xA;&#xA;    // write media container header (if any)&#xA;    ret = avformat_write_header(ofctx, nullptr);&#xA;    if (ret &lt; 0) {&#xA;        std::cerr &lt;&lt; "fail to avformat_write_header: ret=" &lt;&lt; ret;&#xA;        return false;&#xA;    }&#xA;&#xA;    return true;&#xA;}&#xA;</int>