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Richard Stallman et le logiciel libre
19 octobre 2011, par
Mis à jour : Mai 2013
Langue : français
Type : Texte
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Sur d’autres sites (11604)
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Capture and encode desktop with libav in real time not giving corect images
3 septembre 2022, par thoxeyAs part of a larger project I want to be able to capture and encode the desktop frame by frame in real time. I have the following test code to reproduce the issue shown in the screenshot :


#include 
#include 
#include <iostream>
#include <fstream>
#include <string>
#include 
#include 

extern "C"
{
#include "libavdevice/avdevice.h"
#include "libavutil/channel_layout.h"
#include "libavutil/mathematics.h"
#include "libavutil/opt.h"
#include "libavformat/avformat.h"
#include "libswscale/swscale.h"
}


/* 5 seconds stream duration */
#define STREAM_DURATION 5.0
#define STREAM_FRAME_RATE 25 /* 25 images/s */
#define STREAM_NB_FRAMES ((int)(STREAM_DURATION * STREAM_FRAME_RATE))
#define STREAM_PIX_FMT AV_PIX_FMT_YUV420P /* default pix_fmt */

int videoStreamIndx;
int framerate = 30;

int width = 1920;
int height = 1080;

int encPacketCounter;

AVFormatContext* ifmtCtx;
AVCodecContext* avcodecContx;
AVFormatContext* ofmtCtx;
AVStream* videoStream;
AVCodecContext* avCntxOut;
AVPacket* avPkt;
AVFrame* avFrame;
AVFrame* outFrame;
SwsContext* swsCtx;

std::ofstream fs;


AVDictionary* ConfigureScreenCapture()
{

 AVDictionary* options = NULL;
 //Try adding "-rtbufsize 100M" as in https://stackoverflow.com/questions/6766333/capture-windows-screen-with-ffmpeg
 av_dict_set(&options, "rtbufsize", "100M", 0);
 av_dict_set(&options, "framerate", std::to_string(framerate).c_str(), 0);
 char buffer[16];
 sprintf(buffer, "%dx%d", width, height);
 av_dict_set(&options, "video_size", buffer, 0);
 return options;
}

AVCodecParameters* ConfigureAvCodec()
{
 AVCodecParameters* av_codec_par_out = avcodec_parameters_alloc();
 av_codec_par_out->width = width;
 av_codec_par_out->height = height;
 av_codec_par_out->bit_rate = 40000;
 av_codec_par_out->codec_id = AV_CODEC_ID_H264; //AV_CODEC_ID_MPEG4; //Try H.264 instead of MPEG4
 av_codec_par_out->codec_type = AVMEDIA_TYPE_VIDEO;
 av_codec_par_out->format = 0;
 return av_codec_par_out;
}

int GetVideoStreamIndex()
{
 int VideoStreamIndx = -1;
 avformat_find_stream_info(ifmtCtx, NULL);
 /* find the first video stream index . Also there is an API available to do the below operations */
 for (int i = 0; i < (int)ifmtCtx->nb_streams; i++) // find video stream position/index.
 {
 if (ifmtCtx->streams[i]->codecpar->codec_type == AVMEDIA_TYPE_VIDEO)
 {
 VideoStreamIndx = i;
 break;
 }
 }

 if (VideoStreamIndx == -1)
 {
 }

 return VideoStreamIndx;
}

void CreateFrames(AVCodecParameters* av_codec_par_in, AVCodecParameters* av_codec_par_out)
{

 avFrame = av_frame_alloc();
 avFrame->width = avcodecContx->width;
 avFrame->height = avcodecContx->height;
 avFrame->format = av_codec_par_in->format;
 av_frame_get_buffer(avFrame, 0);

 outFrame = av_frame_alloc();
 outFrame->width = avCntxOut->width;
 outFrame->height = avCntxOut->height;
 outFrame->format = av_codec_par_out->format;
 av_frame_get_buffer(outFrame, 0);
}

bool Init()
{
 AVCodecParameters* avCodecParOut = ConfigureAvCodec();

 AVDictionary* options = ConfigureScreenCapture();

 AVInputFormat* ifmt = av_find_input_format("gdigrab");
 auto ifmtCtxLocal = avformat_alloc_context();
 if (avformat_open_input(&ifmtCtxLocal, "desktop", ifmt, &options) < 0)
 {
 return false;
 }
 ifmtCtx = ifmtCtxLocal;

 videoStreamIndx = GetVideoStreamIndex();

 AVCodecParameters* avCodecParIn = avcodec_parameters_alloc();
 avCodecParIn = ifmtCtx->streams[videoStreamIndx]->codecpar;

 AVCodec* avCodec = avcodec_find_decoder(avCodecParIn->codec_id);
 if (avCodec == NULL)
 {
 return false;
 }

 avcodecContx = avcodec_alloc_context3(avCodec);
 if (avcodec_parameters_to_context(avcodecContx, avCodecParIn) < 0)
 {
 return false;
 }

 //av_dict_set
 int value = avcodec_open2(avcodecContx, avCodec, NULL); //Initialize the AVCodecContext to use the given AVCodec.
 if (value < 0)
 {
 return false;
 }

 AVOutputFormat* ofmt = av_guess_format("h264", NULL, NULL);

 if (ofmt == NULL)
 {
 return false;
 }

 auto ofmtCtxLocal = avformat_alloc_context();
 avformat_alloc_output_context2(&ofmtCtxLocal, ofmt, NULL, NULL);
 if (ofmtCtxLocal == NULL)
 {
 return false;
 }
 ofmtCtx = ofmtCtxLocal;

 AVCodec* avCodecOut = avcodec_find_encoder(avCodecParOut->codec_id);
 if (avCodecOut == NULL)
 {
 return false;
 }

 videoStream = avformat_new_stream(ofmtCtx, avCodecOut);
 if (videoStream == NULL)
 {
 return false;
 }

 avCntxOut = avcodec_alloc_context3(avCodecOut);
 if (avCntxOut == NULL)
 {
 return false;
 }

 if (avcodec_parameters_copy(videoStream->codecpar, avCodecParOut) < 0)
 {
 return false;
 }

 if (avcodec_parameters_to_context(avCntxOut, avCodecParOut) < 0)
 {
 return false;
 }

 avCntxOut->gop_size = 30; //3; //Use I-Frame frame every 30 frames.
 avCntxOut->max_b_frames = 0;
 avCntxOut->time_base.num = 1;
 avCntxOut->time_base.den = framerate;

 //avio_open(&ofmtCtx->pb, "", AVIO_FLAG_READ_WRITE);

 if (avformat_write_header(ofmtCtx, NULL) < 0)
 {
 return false;
 }

 value = avcodec_open2(avCntxOut, avCodecOut, NULL); //Initialize the AVCodecContext to use the given AVCodec.
 if (value < 0)
 {
 return false;
 }

 if (avcodecContx->codec_id == AV_CODEC_ID_H264)
 {
 av_opt_set(avCntxOut->priv_data, "preset", "ultrafast", 0);
 av_opt_set(avCntxOut->priv_data, "zerolatency", "1", 0);
 av_opt_set(avCntxOut->priv_data, "tune", "ull", 0);
 }

 if ((ofmtCtx->oformat->flags & AVFMT_GLOBALHEADER) != 0)
 {
 avCntxOut->flags |= AV_CODEC_FLAG_GLOBAL_HEADER;
 }

 CreateFrames(avCodecParIn, avCodecParOut);

 swsCtx = sws_alloc_context();
 if (sws_init_context(swsCtx, NULL, NULL) < 0)
 {
 return false;
 }

 swsCtx = sws_getContext(avcodecContx->width, avcodecContx->height, avcodecContx->pix_fmt,
 avCntxOut->width, avCntxOut->height, avCntxOut->pix_fmt, SWS_FAST_BILINEAR,
 NULL, NULL, NULL);
 if (swsCtx == NULL)
 {
 return false;
 }

 return true;
}

void Encode(AVCodecContext* enc_ctx, AVFrame* frame, AVPacket* pkt)
{
 int ret;

 /* send the frame to the encoder */
 ret = avcodec_send_frame(enc_ctx, frame);
 if (ret < 0)
 {
 return;
 }

 while (ret >= 0)
 {
 ret = avcodec_receive_packet(enc_ctx, pkt);
 if (ret == AVERROR(EAGAIN) || ret == AVERROR_EOF)
 return;
 if (ret < 0)
 {
 return;
 }

 fs.write((char*)pkt->data, pkt->size);
 av_packet_unref(pkt);
 }
}

void EncodeFrames(int noFrames)
{
 int frameCount = 0;
 avPkt = av_packet_alloc();
 AVPacket* outPacket = av_packet_alloc();
 encPacketCounter = 0;

 while (av_read_frame(ifmtCtx, avPkt) >= 0)
 {
 if (frameCount++ == noFrames)
 break;
 if (avPkt->stream_index != videoStreamIndx) continue;

 avcodec_send_packet(avcodecContx, avPkt);

 if (avcodec_receive_frame(avcodecContx, avFrame) >= 0) // Frame successfully decoded :)
 {
 outPacket->data = NULL; // packet data will be allocated by the encoder
 outPacket->size = 0;

 outPacket->pts = av_rescale_q(encPacketCounter, avCntxOut->time_base, videoStream->time_base);
 if (outPacket->dts != AV_NOPTS_VALUE)
 outPacket->dts = av_rescale_q(encPacketCounter, avCntxOut->time_base, videoStream->time_base);

 outPacket->dts = av_rescale_q(encPacketCounter, avCntxOut->time_base, videoStream->time_base);
 outPacket->duration = av_rescale_q(1, avCntxOut->time_base, videoStream->time_base);

 outFrame->pts = av_rescale_q(encPacketCounter, avCntxOut->time_base, videoStream->time_base);
 outFrame->pkt_duration = av_rescale_q(encPacketCounter, avCntxOut->time_base, videoStream->time_base);
 encPacketCounter++;

 int sts = sws_scale(swsCtx,
 avFrame->data, avFrame->linesize, 0, avFrame->height,
 outFrame->data, outFrame->linesize);

 /* make sure the frame data is writable */
 auto ret = av_frame_make_writable(outFrame);
 if (ret < 0)
 break;
 Encode(avCntxOut, outFrame, outPacket);
 }
 av_frame_unref(avFrame);
 av_packet_unref(avPkt);
 }
}

void Dispose()
{
 fs.close();

 auto ifmtCtxLocal = ifmtCtx;
 avformat_close_input(&ifmtCtx);
 avformat_free_context(ifmtCtx);
 avcodec_free_context(&avcodecContx);

}

int main(int argc, char** argv)
{
 avdevice_register_all();

 fs.open("out.h264");

 if (Init())
 {
 EncodeFrames(300);
 }
 else
 {
 std::cout << "Failed to Init \n";
 } 

 Dispose();

 return 0;
}
</string></fstream></iostream>

As far as I can tell the setup of the encoding process is correct as it is largely unchanged from how the example given in the official documentation is working : https://libav.org/documentation/doxygen/master/encode__video_8c_source.html


However there is limited documentation around the desktop capture online so I am not sure if I have set that up correctly.




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Sporadic "Error parsing Cues... Operation not permitted" errors when trying to generate a DASH manifest
22 novembre 2023, par kshetlineI have already-generated .webm audio and video files (1 audio, 3 video resolutions for each video I want to stream). The video has been generated not (directly) by ffmpeg, but HandbrakeCLI 1.7.0, with V9 encoding. The audio (which has never caused an error) is generated by ffmpeg using libvorbis.


Most of the time ffmpeg (version 6.1) creates a manifest without any problem. Sporadically, however, "Error parsing Cues" comes up (frequently with the latest videos I've been trying to process) and I can't create a manifest. Since this is happening during an automated process to process many videos for streaming, the audio and video sources are being created exactly the same way whether ffmpeg succeeds or fails in generating a manifest, making this all the more confusing.


The video files ffmpeg chokes on play perfectly well using VLC, and mediainfo doesn't show any problems with these files.


Here's the way I've been (sometimes successfully, sometimes not) generating a manifest, with extra logging added :


ffmpeg -v 9 -loglevel 99 \
 -f webm_dash_manifest -i '.\Sample Video.v480.webm' \
 -f webm_dash_manifest -i '.\Sample Video.v720.webm' \
 -f webm_dash_manifest -i '.\Sample Video.v1080.webm' \
 -f webm_dash_manifest -i '.\Sample Video.audio.webm' \
 -c copy -map 0 -map 1 -map 2 -map 3 \
 -f webm_dash_manifest -adaptation_sets "id=0,streams=0,1,2 id=1,streams=3" \
 '.\Sample Video.mpd'


Here's the result when it fails :


ffmpeg version 6.1-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-static --pkg-config=pkgconf --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-libaribcaption --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-libharfbuzz --enable-liblensfun --enable-libvidstab --enable-libvmaf --enable-libzimg --enable-amf --enable-cuda-llvm --enable-cuvid --enable-ffnvcodec --enable-nvdec --enable-nvenc --enable-dxva2 --enable-d3d11va --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-libcodec2 --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. 29.100 / 58. 29.100
 libavcodec 60. 31.102 / 60. 31.102
 libavformat 60. 16.100 / 60. 16.100
 libavdevice 60. 3.100 / 60. 3.100
 libavfilter 9. 12.100 / 9. 12.100
 libswscale 7. 5.100 / 7. 5.100
 libswresample 4. 12.100 / 4. 12.100
 libpostproc 57. 3.100 / 57. 3.100
Splitting the commandline.
Reading option '-v' ... matched as option 'v' (set logging level) with argument '9'.
Reading option '-loglevel' ... matched as option 'loglevel' (set logging level) with argument '99'.
Reading option '-f' ... matched as option 'f' (force format) with argument 'webm_dash_manifest'.
Reading option '-i' ... matched as output url with argument '.\Sample Video.v480.webm'.
Reading option '-f' ... matched as option 'f' (force format) with argument 'webm_dash_manifest'.
Reading option '-i' ... matched as output url with argument '.\Sample Video.v720.webm'.
Reading option '-f' ... matched as option 'f' (force format) with argument 'webm_dash_manifest'.
Reading option '-i' ... matched as output url with argument '.\Sample Video.v1080.webm'.
Reading option '-f' ... matched as option 'f' (force format) with argument 'webm_dash_manifest'.
Reading option '-i' ... matched as output url with argument '.\Sample Video.audio.webm'.
Reading option '-c' ... matched as option 'c' (codec name) with argument 'copy'.
Reading option '-map' ... matched as option 'map' (set input stream mapping) with argument '0'.
Reading option '-map' ... matched as option 'map' (set input stream mapping) with argument '1'.
Reading option '-map' ... matched as option 'map' (set input stream mapping) with argument '2'.
Reading option '-map' ... matched as option 'map' (set input stream mapping) with argument '3'.
Reading option '-f' ... matched as option 'f' (force format) with argument 'webm_dash_manifest'.
Reading option '-adaptation_sets' ... matched as AVOption 'adaptation_sets' with argument 'id=0,streams=0,1,2 id=1,streams=3'.
Reading option '.\Sample Video.mpd' ... matched as output url.
Finished splitting the commandline.
Parsing a group of options: global .
Applying option v (set logging level) with argument 9.
Successfully parsed a group of options.
Parsing a group of options: input url .\Sample Video.v480.webm.
Applying option f (force format) with argument webm_dash_manifest.
Successfully parsed a group of options.
Opening an input file: .\Sample Video.v480.webm.
[webm_dash_manifest @ 000002bbcb41dc80] Opening '.\Sample Video.v480.webm' for reading
[file @ 000002bbcb41e300] Setting default whitelist 'file,crypto,data'
st:0 removing common factor 1000000 from timebase
[webm_dash_manifest @ 000002bbcb41dc80] Error parsing Cues
[AVIOContext @ 000002bbcb41e5c0] Statistics: 102283 bytes read, 4 seeks
[in#0 @ 000002bbcb41dac0] Error opening input: Operation not permitted
Error opening input file .\Sample Video.v480.webm.
Error opening input files: Operation not permitted


This is
mediainfofor the offending input file, Sample Video.v480.webm :

General
Complete name : .\Sample Video.v480.webm
Format : WebM
Format version : Version 2
File size : 628 MiB
Duration : 1 h 34 min
Overall bit rate : 926 kb/s
Frame rate : 23.976 FPS
Encoded date : 2023-11-21 16:48:35 UTC
Writing application : HandBrake 1.7.0 2023111500
Writing library : Lavf60.16.100

Video
ID : 1
Format : VP9
Format profile : 0
Codec ID : V_VP9
Duration : 1 h 34 min
Bit rate : 882 kb/s
Width : 720 pixels
Height : 480 pixels
Display aspect ratio : 16:9
Frame rate mode : Constant
Frame rate : 23.976 (24000/1001) FPS
Color space : YUV
Chroma subsampling : 4:2:0
Bit depth : 8 bits
Bits/(Pixel*Frame) : 0.106
Stream size : 598 MiB (95%)
Default : Yes
Forced : No
Color range : Limited
Color primaries : BT.709
Transfer characteristics : BT.709
Matrix coefficients : BT.709


I don't know if I need different command line options, or whether this might be an ffmpeg or Handbrake bug. It has taken many, many hours to generate these video files (VP9 is painfully slow to encode), so I hate to do a lot of this over again, especially doing it again encoding the video with ffmpeg instead of Handbrake, as Handbrake is (oddly enough, considering it uses ffmpeg under the hood) noticeably faster.


I have no idea what these "Cues" are that ffmpeg wants and can't parse, or how I would change them.


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