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• libswresample : Why does swr_init() change |in_ch_layout| order so it no longer matches my decoded AVFrames, causing resampling to fail ?

  20 novembre 2023, par CheekyChips

  I am trying to write some code that resamples an audio file to 16kHz and 1 channel and then encodes it to PCM, but I am having an issue with channel layouts.

  


  In a nutshell :

  


  My AVCodecContext and the frames I get from the stream via avcodec_receive_frame() have a channel layout order of AV_CHANNEL_ORDER_UNSPEC. But when I call swr_init() it changes the in_ch_layout order to AV_CHANNEL_ORDER_NATIVE. Then when I call swr_convert_frame() with my AVFrames, because the channel layout orders don't match, the resampling fails because it thinks the input changed.

  


  More details :

  


  I create an AVCodecContext from my audio stream's codec, and it has a channel layout of AV_CHANNEL_ORDER_UNSPEC with 2 channels, and any frames I decode from the stream via avcodec_receive_frame() also have a channel layout order of AV_CHANNEL_ORDER_UNSPEC.

  


  I set SwrContext's |in_ch_layout| to the sample channel layout from the codec context :

  


      AVChannelLayout in_ch_layout = in_codec_context->ch_layout,
    ...
    int ret = swr_alloc_set_opts2(&swr_ctx, ...
                      &in_ch_layout,
                      ...);


  


  But SwrContext->init() changes its internal in_ch_layout from AV_CHANNEL_ORDER_UNSPEC to AV_CHANNEL_ORDER_NATIVE meaning it fails the next time I call swr_convert_frame() because the input frame has a different channel layout to the SwrContext. When swr_init() is called (in my case indirectly by swr_convert_frame(), but also if I alternatively call it directly) the SwrContext->used_ch_layout and SwrContext->in_ch_layout are updated to have channel layout order of AV_CHANNEL_ORDER_NATIVE :

  


      // swresample.c
    av_cold int swr_init(struct SwrContext *s){
        ...
        if (!av_channel_layout_check(&s->used_ch_layout))       <-- This hits if I don't set anything for used_ch_layout
            av_channel_layout_default(&s->used_ch_layout, s->in.ch_count);      <-- default is AV_CHANNEL_ORDER_NATIVE
        ...
        if (s->used_ch_layout.order == AV_CHANNEL_ORDER_UNSPEC) <-- This hits if I do set used_ch_layout
            av_channel_layout_default(&s->used_ch_layout, s->used_ch_layout.nb_channels);   <-- default is AV_CHANNEL_ORDER_NATIVE


  


  Then when I next call swr_convert_frame(), because the frame has the same layout as the audio stream's codec (AV_CHANNEL_ORDER_UNSPEC), and this is different to SwrContext->in_ch_layout (AV_CHANNEL_ORDER_NATIVE), it early exits with ret |= AVERROR_INPUT_CHANGED.

  


  // swresample_frame.c
    int swr_convert_frame(SwrContext *s,
                      AVFrame *out, const AVFrame *in)
    {
        ...
        if ((ret = config_changed(s, out, in)))
            return ret;
        ...


  


      static int config_changed(SwrContext *s,
                            const AVFrame *out, const AVFrame *in)
    {
        ...
        if ((err = av_channel_layout_copy(&ch_layout, &in->ch_layout)) < 0)
            ...
        if (av_channel_layout_compare(&s->in_ch_layout, &ch_layout) || ...) {   <-- This hits the next time I call swr_convert_frame()
            ret |= AVERROR_INPUT_CHANGED;
        }


  


      // channel_layout.c
    int av_channel_layout_compare(const AVChannelLayout *chl, const AVChannelLayout *chl1)
    {
        ...
        // if only one is unspecified -> not equal
        if ((chl->order  == AV_CHANNEL_ORDER_UNSPEC) !=
            (chl1->order == AV_CHANNEL_ORDER_UNSPEC))
            return 1;


  


  If I hardcode the channel layout order of each input AVFrame to AV_CHANNEL_ORDER_NATIVE before resampling, then the resampling and subsequent encoding works, but this feels like a really bad idea and of course wouldn't work as soon as I resample an audio file with a different channel layout.

  


      avcodec_receive_frame(in_codec_context, input_frame);

    AVChannelLayout input_frame_ch_layout;
    av_channel_layout_default(&input_frame_ch_layout, 2 /* = nb_channels*/);
    input_frame->ch_layout = input_frame_ch_layout;
    // Bad idea - but "fixes" my issue!


  


  My questions

  


  What do I need to do to the resampler OR/AND the decoded audio frame to make sure they have the same channel layout order and the resampling works ?

  


  How can I make the channel order of the AVFrames that I get from avcodec_receive_frame() match the input channel order of SwrContext so the resampling works ? My understanding is that the decoded frames should be 'correct' already and I shouldn't need to change any of their values, only values of the output (resampled) frames that I create.

  


  Is there something I need to set on the AVFrame before I resample it ?

  


  Why does the SwrContext choose to change the channel order to AV_CHANNEL_ORDER_NATIVE ?

  


  Note :
A workaround could be to use swr_convert() with the raw data buffer instead of swr_convert_frame(), since it looks like it bypasses this check (since there are no frames involved). I haven't tried this but this shouldn't be necessary and I would like to use swr_convert_frame() as I am working with input and output frames.

  


  Unfortunately I can't find example code using swr_convert_frame() (not even the ffmpeg code seems to ever call it).

  


  My full c++ source code
(error handling omitted for readability) :

  


  std::string fileToUse = "/home/projects/audioFileProject/Audio files/14 Black Cadillacs.wma";
const std::string outputFilename = "out.wav";
const std::string PCMS16BE_encoder_name = "pcm_f32le";

int main()
{
    // Open audio file
    AVFormatContext* in_format_context = avformat_alloc_context();
    avformat_open_input(&in_format_context, fileToUse.c_str(), NULL, NULL);
    avformat_find_stream_info(in_format_context, NULL);
    
    // Get audio stream from file and corresponding decoder
    AVStream* in_stream = in_format_context->streams[0];
    AVCodecParameters* codec_params = in_stream->codecpar;
    const AVCodec* in_codec = avcodec_find_decoder(codec_params->codec_id);
    AVCodecContext *in_codec_context = avcodec_alloc_context3(in_codec);
    avcodec_parameters_to_context(in_codec_context, codec_params);
    avcodec_open2(in_codec_context, in_codec, NULL);

    // Prepare output stream and output encoder (PCM)
    AVFormatContext* out_format_context = nullptr;
    avformat_alloc_output_context2(&out_format_context, NULL, NULL, outputFilename.c_str());
    AVStream* out_stream = avformat_new_stream(out_format_context, NULL);
    const AVCodec* output_codec = avcodec_find_encoder_by_name(PCMS16BE_encoder_name.c_str());
    AVCodecContext* output_codec_context = avcodec_alloc_context3(output_codec);

    // -------------------------------
    
    AVChannelLayout output_ch_layout;
    av_channel_layout_default(&output_ch_layout, 1);    // AV_CHANNEL_LAYOUT_MONO
    output_codec_context->ch_layout = output_ch_layout;
    
    auto out_sample_rate = 16000;
    output_codec_context->sample_rate = out_sample_rate;
    output_codec_context->sample_fmt = output_codec->sample_fmts[0];
    //output_codec_context->bit_rate = output_codec_context->bit_rate;  // TODO Do we need to set the bit rate?
    output_codec_context->time_base = (AVRational){1, out_sample_rate};
    out_stream->time_base = output_codec_context->time_base;

    auto in_sample_rate = in_codec_context->sample_rate;
    AVChannelLayout in_ch_layout = in_codec_context->ch_layout,
                    out_ch_layout = output_ch_layout;   // AV_CHANNEL_LAYOUT_MONO;
    enum AVSampleFormat in_sample_fmt = in_codec_context->sample_fmt,
                        out_sample_fmt = in_codec_context->sample_fmt;

    SwrContext *swr_ctx = nullptr;
    int ret = swr_alloc_set_opts2(&swr_ctx,
                      &out_ch_layout,
                      out_sample_fmt,
                      out_sample_rate,
                      &in_ch_layout,
                      in_sample_fmt,
                      in_sample_rate,
                      0,                    // log_offset
                      NULL);                // log_ctx

    // Probably not necessary - documentation says "This option is
only used for special remapping."
    av_opt_set_chlayout(swr_ctx,    "used_chlayout",     &in_ch_layout, 0);

    // Open output file for writing
    avcodec_open2(output_codec_context, output_codec, NULL);
    avcodec_parameters_from_context(out_stream->codecpar, output_codec_context);
    
    if (out_format_context->oformat->flags & AVFMT_GLOBALHEADER)
        out_format_context->flags |= AV_CODEC_FLAG_GLOBAL_HEADER;

    avio_open(&out_format_context->pb, outputFilename.c_str(), AVIO_FLAG_WRITE);
    AVDictionary* muxer_opts = nullptr;
    avformat_write_header(out_format_context, &muxer_opts);

    AVFrame* input_frame = av_frame_alloc();
    AVPacket* in_packet = av_packet_alloc();

    // Loop through decoded input frames. Resample and get resulting samples in a new output frame.
    // I think PCM supports variable number of samples in frames so probably can immediately write out
    while (av_read_frame(in_format_context, in_packet) >= 0) {
        avcodec_send_packet(in_codec_context, in_packet);
        avcodec_receive_frame(in_codec_context, input_frame);

        // I don't want to do this, but it 'fixes' the error where channel layout of input frames
        // doesn't match what the resampler expects - hardcoded the number 2 to fit my sample audio file.
        AVChannelLayout input_frame_ch_layout;
        av_channel_layout_default(&input_frame_ch_layout, 2 /* = nb_channels*/);
        input_frame->ch_layout = input_frame_ch_layout;

        AVFrame* output_frame = av_frame_alloc();
        output_frame->sample_rate = out_sample_rate;
        output_frame->format = out_sample_fmt;
        output_frame->ch_layout = out_ch_layout;
        output_frame->nb_samples = output_codec_context->frame_size;
        
        // TODO Probably need to do maths to calculate new pts properly
        output_frame->pts = input_frame->pts;

        if (swr_convert_frame(swr_ctx, output_frame, input_frame))
            {   logging("Swr Convert failed");  return -1;   }          
            /// ^ Fails here, the second time (since the first time init() is called internally)

        AVPacket *output_packet = av_packet_alloc();
        int response = avcodec_send_frame(output_codec_context, output_frame);

        while (response >= 0) {
            response = avcodec_receive_packet(output_codec_context, output_packet);

            if (response == AVERROR(EAGAIN) || response == AVERROR_EOF) {
                break;
            }

            output_packet->stream_index = 0;
            av_packet_rescale_ts(output_packet, in_stream->time_base, out_stream->time_base);
            av_interleaved_write_frame(out_format_context, output_packet);
        }
        av_packet_unref(output_packet);
        av_packet_free(&output_packet);
        av_frame_unref(input_frame);    // Free references held by the frame before reading new data into it.
        av_frame_unref(output_frame);
    }
    // TODO write last output packet flushing the buffer

    avformat_close_input(&in_format_context);
    return 0;
}


  


• How to make Matomo GDPR compliant in 12 steps

  3 avril 2018, par InnoCraft

  Important note : this blog post has been written by digital analysts, not lawyers. The purpose of this article is to briefly show you where Matomo is entering into play within the GDPR process. This work comes from our interpretation of the UK privacy commission : ICO. It cannot be considered as professional legal advice. So as GDPR, this information is subject to change. We strongly advise you to have a look at the different privacy authorities in order to have up to date information.

  The General Data Protection Regulation (EU) 2016/679, also referred to RGPD in French, Datenschutz-Grundverordnung, DS-GVO in German, is a regulation on data protection and privacy for all individuals within the European Union. It concerns organizations worldwide dealing with EU citizens and will come into force on the 25th May 2018.

  The GDPR applies to ‘personal data’ meaning any information relating to an identifiable person who can be directly or indirectly identified in particular by reference to an identifier. It includes cookies, IP addresses, User ID, location, and any other data you may have collected.

  We will list below the 12 steps recommended by the UK privacy commissioner in order to be GDPR compliant and what you need to do for each step.

  The 12 steps of GDPR compliance according to ICO and how it fit with Matomo

  As mentioned in one of our previous blog post about GDPR, if you are not collecting any personal data with Matomo, then you are not concerned about what is written below.

  If you are processing personal data in any way, here are the 12 steps to follow along with some recommendations on how to be GDPR compliant with Matomo :

  1 – Awareness

  Make sure that people within your organization know that you are using Matomo in order to analyze traffic on the website/app. If needed, send them the link to the “What is Matomo ?” page.

  2 – Information you hold

  List all the personal data you are processing with Matomo within your record of processing activities. We are personally using the template provided by ICO which is composed of a set of 30 questions you need to answer regarding your use of Matomo. We have published an article which walks you through the list of questions specifically in the use case of Matomo Analytics. Please be aware that personal data may be also tracked in non-obvious ways for example as part of page URLs or page titles.

  3 – Communicating privacy information

  a – Add a privacy notice

  Add a privacy notice wherever you are using Matomo in order to collect personal data. Please refer to the ICO documentation in order to learn how to write a privacy notice. You can learn more in our article about creating your privacy notice for Matomo Analytics. Make sure that a privacy policy link is always available on your website or app.

  b – Add Matomo to your privacy policy page

  Add Matomo to the list of technologies you are using on your privacy policy page and add all the necessary information to it as requested in the following checklist. To learn more check out our article about Privacy policy.

  4 – Individuals’ rights

  Make sure that your Matomo installation respects all the individuals’ rights. To make it short, you will need to know the features in Matomo that you need to use to respect user rights (right of access, right of rectification, right of erasure…). These features are available starting in Matomo 3.5.0 released on May 8th : GDPR tools for Matomo (User guide).

  5 – Subject access requests

  Make sure that you are able to answer an access request from a data subject for Matomo. For example, when a person would like to access her or his personal data that you have collected about her or him, then you will need to be you able to provide her or him with this information. We recommend you design a process for this like “Who is dealing with it ?” and check that it is working. If you can answer to the nightmare letter, then you are ready. The needed features for this in Matomo will be available soon.

  6 – Lawful basis for processing personal data

  There are different lawful basis you can use under GDPR. It can be either “Legitimate interest” or “Explicit consent”. Do not forget to mention it within your privacy policy page. Read more in our article about lawful basis.

  7 – Consent

  Users should be able to remove their consent at any time. By chance, Matomo is providing a feature in order to do just that : add the opt-out feature to your privacy policy page.
  We are also offering a tool that allows you optionally to require consent before any data is tracked. This will be useful if a person should be only tracked after she or he has given explicit consent to be tracked.

  8 – Children

  If your website or app is targeted for children and you are using Matomo, extra measures will need to be taken. For example you will need to write your privacy policy even more clear and moreover getting parents consent if the child is below 13. As it is a very specific case, we strongly recommend you to follow this link for further information.

  9 – Data breaches

  As you may be collecting personal data with Matomo, you should also check your “data breach procedure” to define if a leak may have consequences on the privacy of the data subject. Please consult ICO’s website for further information.

  10 – Data Protection by Design and Data Protection Impact Assessments

  Ask yourself if you really need to process personal data within Matomo. If the data you are processing within Matomo is sensitive, we strongly recommend you to make a Data Protection Impact Assessment. A software is available from the The open source PIA software helps to carry out data protection impact assessment, by French Privacy Commissioner : CNIL.

  11 – Data Protection Officers

  If you are reading this article and you are the Data Protection Officer (DPO), you will not be concerned by this step. If that’s not the case, your duty is to provide to the DPO (if your business has a DPO) our blog post in order for her or him to ask you questions regarding your use of Matomo. Note that your DPO can also be interested in the different data that Matomo can process : “What data does Matomo track ?” (FAQ).

  12 – International

  Matomo data is hosted wherever you want. So according to the location of the data, you will need to show specific safeguard except for EU. For example regarding the USA, you will have to check if your web hosting platform is registered to the Privacy Shield : privacyshield.gov/list
  Note : our Matomo cloud infrastructure is based in France.

  That’s the end of this blog post. As GDPR is a huge topic, we will release many more blog posts in the upcoming weeks. If there are any Matomo GDPR topic related posts you would like us to write, please feel free to contact us.

  The post How to make Matomo GDPR compliant in 12 steps appeared first on Analytics Platform - Matomo.

• Files created with "ffmpeg hevc_nvenc" do not play on TV. (with video codec SDK 9.1 of nvidia)

  29 janvier 2020, par Dashhh

  Problem

  • Files created with hevc_nvenc do not play on TV. (samsung smart tv, model unknown)
    Related to my ffmpeg build is below.

  FFmpeg build conf

  $ ffmpeg -buildconf
  
      --enable-cuda
  
      --enable-cuvid
  
      --enable-nvenc
  
      --enable-nonfree
  
      --enable-libnpp
  
      --extra-cflags=-I/path/cuda/include
  
      --extra-ldflags=-L/path/cuda/lib64
  
      --prefix=/prefix/ffmpeg_build
  
      --pkg-config-flags=--static
  
      --extra-libs='-lpthread -lm'
  
      --extra-cflags=-I/prefix/ffmpeg_build/include
  
      --extra-ldflags=-L/prefix/ffmpeg_build/lib
  
      --enable-gpl
  
      --enable-nonfree
  
      --enable-version3
  
      --disable-stripping
  
      --enable-avisynth
  
      --enable-libass
  
      --enable-libfontconfig
  
      --enable-libfreetype
  
      --enable-libfribidi
  
      --enable-libgme
  
      --enable-libgsm
  
      --enable-librubberband
  
      --enable-libshine
  
      --enable-libsnappy
  
      --enable-libssh
  
      --enable-libtwolame
  
      --enable-libwavpack
  
      --enable-libzvbi
  
      --enable-openal
  
      --enable-sdl2
  
      --enable-libdrm
  
      --enable-frei0r
  
      --enable-ladspa
  
      --enable-libpulse
  
      --enable-libsoxr
  
      --enable-libspeex
  
      --enable-avfilter
  
      --enable-postproc
  
      --enable-pthreads
  
      --enable-libfdk-aac
  
      --enable-libmp3lame
  
      --enable-libopus
  
      --enable-libtheora
  
      --enable-libvorbis
  
      --enable-libvpx
  
      --enable-libx264
  
      --enable-libx265
  
      --disable-ffplay
  
      --enable-libopenjpeg
  
      --enable-libwebp
  
      --enable-libxvid
  
      --enable-libvidstab
  
      --enable-libopenh264
  
      --enable-zlib
  
      --enable-openssl

  ---

  ffmpeg Command

  • Command about FFmpeg encoding

  ffmpeg -ss 1800 -vsync 0 -hwaccel cuvid -hwaccel_device 0 \
  
  -c:v h264_cuvid -i /data/input.mp4 -t 10 \
  
  -filter_complex "\
  
  [0:v]hwdownload,format=nv12,format=yuv420p,\
  
  scale=iw*2:ih*2" -gpu 0 -c:v hevc_nvenc -pix_fmt yuv444p16le -preset slow -rc cbr_hq -b:v 5000k -maxrate 7000k -bufsize 1000k -acodec aac -ac 2 -dts_delta_threshold 1000 -ab 128k -flags global_header ./makevideo_nvenc_hevc.mp4

  Full log about This Command - check this full log

  The reason for adding "-color_ " in the command is as follows.

  • HDR video after creating bt2020 + smpte2084 video using nvidia hardware accelerator. (I’m studying to make HDR videos. I’m not sure if this is right.)

  How can I make a video using ffmpeg hevc_nvenc and have it play on TV ?

  ---

  Things i’ve done

  Here’s what I’ve researched about why it doesn’t work.
   The header information is not properly included in the resulting video file. So I used a program called nvhsp to add SEI and VUI information inside the video. See below for the commands and logs used.

  nvhsp is open source for writing VUI and SEI bitstrings in raw video. nvhsp link

  # make rawvideo for nvhsp
  
  $  ffmpeg -vsync 0 -hwaccel cuvid -hwaccel_device 0 -c:v h264_cuvid \
  
  -i /data/input.mp4 -t 10 \
  
  -filter_complex "[0:v]hwdownload,format=nv12,\
  
  format=yuv420p,scale=iw*2:ih*2" \
  
  -gpu 0 -c:v hevc_nvenc -f rawvideo output_for_nvhsp.265
  
  
  
  # use nvhsp
  
  $ python nvhsp.py ./output_for_nvhsp.265 -colorprim bt2020 \
  
  -transfer smpte-st-2084 -colormatrix bt2020nc \
  
  -maxcll "1000,300" -videoformat ntsc -full_range tv \
  
  -masterdisplay "G (13250,34500) B (7500,3000 ) R (34000,16000) WP (15635,16450) L (10000000,1)" \
  
  ./after_nvhsp_proc_output.265
  
  
  
  Parsing the infile:
  
  
  
  ==========================
  
  
  
  Prepending SEI data
  
  Starting new SEI NALu ...
  
  SEI message with MaxCLL = 1000 and MaxFall = 300 created in SEI NAL
  
  SEI message Mastering Display Data G (13250,34500) B (7500,3000) R (34000,16000) WP (15635,16450) L (10000000,1) created in SEI NAL
  
  Looking for SPS ......... [232, 22703552]
  
  SPS_Nals_addresses [232, 22703552]
  
  SPS NAL Size 488
  
  Starting reading SPS NAL contents
  
  Reading of SPS NAL finished. Read 448 of SPS NALu data.
  
  
  
  Making modified SPS NALu ...
  
  Made modified SPS NALu-OK
  
  New SEI prepended
  
  Writing new stream ...
  
  Progress: 100%
  
  =====================
  
  Done!
  
  
  
  File nvhsp_after_output.mp4 created.
  
  
  
  # after process
  
  $ ffmpeg -y -f rawvideo -r 25 -s 3840x2160 -pix_fmt yuv444p16le -color_primaries bt2020 -color_trc smpte2084  -colorspace bt2020nc -color_range tv -i ./1/after_nvhsp_proc_output.265 -vcodec copy  ./1/result.mp4 -hide_banner
  
  
  
  Truncating packet of size 49766400 to 3260044
  
  [rawvideo @ 0x40a6400] Estimating duration from bitrate, this may be inaccurate
  
  Input #0, rawvideo, from './1/nvhsp_after_output.265':
  
    Duration: N/A, start: 0.000000, bitrate: 9953280 kb/s
  
      Stream #0:0: Video: rawvideo (Y3[0][16] / 0x10003359), yuv444p16le(tv, bt2020nc/bt2020/smpte2084), 3840x2160, 9953280 kb/s, 25 tbr, 25 tbn, 25 tbc
  
  [mp4 @ 0x40b0440] Could not find tag for codec rawvideo in stream #0, codec not currently supported in container
  
  Could not write header for output file #0 (incorrect codec parameters ?): Invalid argument
  
  Stream mapping:
  
    Stream #0:0 -> #0:0 (copy)
  
      Last message repeated 1 times

  Goal

  • I want to generate matadata normally when encoding a video through hevc_nvenc.

  • I want to create a video through hevc_nvenc and play HDR Video on smart tv with 10bit color depth support.

  ---

  Additional

  • Is it normal for ffmpeg hevc_nvenc not to generate metadata in the resulting video file ? or is it a bug ?

  • Please refer to the image below. (*’알 수 없음’ meaning ’unknown’)

    • if you need more detail file info, check this Gist Link (by ffprobe)
      

  • However, if you encode a file in libx265, the attribute information is entered correctly as shown below.

    • if you need more detail file info, check this Gist Link
      

  However, when using hevc_nvenc, all information is missing.

  • i used option -show_streams -show_programs -show_format -show_data -of json -show_frames -show_log 56 at ffprobe