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La conservation du net art au musée. Les stratégies à l’œuvre
26 mai 2011
Mis à jour : Juillet 2013
Langue : français
Type : Texte
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Publier sur MédiaSpip
13 juin 2013Puis-je poster des contenus à partir d’une tablette Ipad ?
Oui, si votre Médiaspip installé est à la version 0.2 ou supérieure. Contacter au besoin l’administrateur de votre MédiaSpip pour le savoir -
Le plugin : Podcasts.
14 juillet 2010, parLe problème du podcasting est à nouveau un problème révélateur de la normalisation des transports de données sur Internet.
Deux formats intéressants existent : Celui développé par Apple, très axé sur l’utilisation d’iTunes dont la SPEC est ici ; Le format "Media RSS Module" qui est plus "libre" notamment soutenu par Yahoo et le logiciel Miro ;
Types de fichiers supportés dans les flux
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Sur d’autres sites (4733)
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OpenCV 4.5.2 takes a long time (>100ms) to retrieve a single frame from a webcam, C++ on Windows 10
9 juin 2021, par Mustard TigerI've been having a tough time getting my webcam working quickly with opencv. Frames take a very long time to read, (a recorded average of 124ms across 500 frames) I've tried on three different computers (running Windows 10) with a logitech C922 webcam. The most recent machine I tested on has a Ryzen 9 3950X, with 32gbs of ram ; no lack of power.


Here is the code :


cv::VideoCapture cap = cv::VideoCapture(m_cameraNum);

// Check if camera opened successfully
if (!cap.isOpened())
{
 m_logger->critical("Error opening video stream or file\n\r");
 return -1;
}

bool result = true;
result &= cap.set(cv::CAP_PROP_FRAME_WIDTH, 1280);
result &= cap.set(cv::CAP_PROP_FRAME_HEIGHT, 720);

bool ready = false;
std::vector<string> timeLog;
timeLog.reserve(50000);
int i = 0;

while (i < 500)
{
 auto start = std::chrono::system_clock::now();
 
 cv::Mat img;
 ready = cap.read(img);

 // If the frame is empty, break immediately
 if (!ready)
 {
 timeLog.push_back("continue");
 continue;
 }

 i++;
 auto end = std::chrono::system_clock::now();
 timeLog.push_back(std::to_string(std::chrono::duration_cast(end - start).count()));
}

for (auto& entry : timeLog)
 m_logger->info(entry);

cap.release();
return 0;
</string>

Notice that I write the elapsed time to a log file at the end of execution. The average time is 124ms for debug and release, and not one instance of "continue" after half a dozen runs.


It doesn't matter if I use USB 2 or USB 3 ports (the camera is USB2) or if I run a debug build or a release build, the log file will show anywhere from 110ms to 130ms of time for each frame. The camera works fine in other app, OBS can get a smooth 1080@30fps or 720@60fps.


Stepping through the debugger and doing a lot of Googling, I've learned the following about my system :


- 

- The backend chosen by default is DSHOW. GStreamer and FFMPEG are also available.
- DSHOW uses FFMPEG somehow (it needs the FFMPEG dll) but I cannot use FFMPEG directly through opencv. Attempting to use cv::VideoCapture(m_cameraNum, cv::CAP_FFMPEG) always fails. It seems like Opencv's interface to FFMPEG is only capable of opening video files.
- Microsoft really screwed up camera devices in Windows a few years back, not sure if this is related to my problem.








Here's a short list of the fixes I have tried, most taken from older SO posts :


- 

- result &= cap.set(cv::CAP_PROP_FRAME_COUNT, 30) ; // Returns false, does nothing
- result &= cap.set(cv::CAP_PROP_CONVERT_RGB, 0) ; // Returns true, does nothing
- result &= cap.set(cv::CAP_PROP_MODE, cv::VideoWriter::fourcc('M', 'J', 'P', 'G')) ; // Returns false, does nothing
- Set registry key from http://alax.info/blog/1693 that should disable the new Windows camera server.
- Updated from 4.5.0 to 4.5.2, no change.
- Asked device manager to find a newer driver, no newer driver found.














I'm out of ideas. Any help ?


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FFmpeg av_dump_format showing incorrect output, but ffprobe displays correct metadata
29 janvier, par グルグルI use ffmpeg 7.1 source build on windows and compilation configuration as follow :


configuration:
 --toolchain=msvc
 --arch=x86_64
 --enable-x86asm
 --enable-asm
 --enable-shared
 --enable-w32threads
 --prefix=/D/build


When I use
av_dump_formatto print metadata of test.mp3, it display the incorrect information.

extern "C"
{
#include <libavformat></libavformat>avformat.h>
}

int main()
{ 
 av_log_set_level(AV_LOG_DEBUG);

 auto url = "D:/music/test.mp3";

 AVFormatContext* fmt;
 auto ret = avformat_open_input(&fmt, url, nullptr, nullptr);
 if (ret < 0)
 {
 av_log(nullptr, AV_LOG_ERROR, "Cannot open %s format : %s", url, av_err2str(ret));
 exit(EXIT_FAILURE);
 }

 av_dump_format(fmt, 0, url, 0);
}


output


[AVFormatContext @ 000001768E65BC40] Opening 'D:/music/test.mp3' for reading
[file @ 000001768E65C180] Setting default whitelist 'file,crypto,data'
[mp3 @ 000001768E65BC40] Format mp3 probed with size=4096 and score=51
id3v2 ver:4 flags:00 len:35
[mp3 @ 000001768E65BC40] pad 576 576
[mp3 @ 000001768E65BC40] Skipping 0 bytes of junk at 462.
Input #0, mp3, from 'D:/music/test.mp3':
 Metadata:
 encoder : Lavf58.76.100
 Duration: N/A, bitrate: N/A
 Stream #0:0, 0, 1/14112000: Audio: mp3, 0 channels
 Metadata:
 encoder : Lavc58.13


You can see the Stream info is useless.


But I use ffprobe which is built with same configuration to print metadata of test.mp3.


It's display normal.


ffprobe version 7.0.1 Copyright (c) 2007-2024 the FFmpeg developers
 built with Microsoft (R) C/C++ Optimizing Compiler Version 19.41.34123 for x64
 configuration: --toolchain=msvc --arch=x86_64 --enable-x86asm --enable-asm --enable-shared --enable-w32threads --prefix=/D/build
 WARNING: library configuration mismatch
 avutil configuration: --toolchain=msvc --arch=x86_64 --enable-x86asm --enable-asm --enable-shared --enable-w32threads --disable-programs --disable-doc --disable-static --prefix=/D/build
 avcodec configuration: --toolchain=msvc --arch=x86_64 --enable-x86asm --enable-asm --enable-shared --enable-w32threads --disable-programs --disable-doc --disable-static --prefix=/D/build
 avformat configuration: --toolchain=msvc --arch=x86_64 --enable-x86asm --enable-asm --enable-shared --enable-w32threads --disable-programs --disable-doc --disable-static --prefix=/D/build
 avdevice configuration: --toolchain=msvc --arch=x86_64 --enable-x86asm --enable-asm --enable-shared --enable-w32threads --disable-programs --disable-doc --disable-static --prefix=/D/build
 avfilter configuration: --toolchain=msvc --arch=x86_64 --enable-x86asm --enable-asm --enable-shared --enable-w32threads --disable-programs --disable-doc --disable-static --prefix=/D/build
 swscale configuration: --toolchain=msvc --arch=x86_64 --enable-x86asm --enable-asm --enable-shared --enable-w32threads --disable-programs --disable-doc --disable-static --prefix=/D/build
 swresample configuration: --toolchain=msvc --arch=x86_64 --enable-x86asm --enable-asm --enable-shared --enable-w32threads --disable-programs --disable-doc --disable-static --prefix=/D/build
 libavutil 59. 8.100 / 59. 39.100
 libavcodec 61. 3.100 / 61. 19.100
 libavformat 61. 1.100 / 61. 7.100
 libavdevice 61. 1.100 / 61. 3.100
 libavfilter 10. 1.100 / 10. 4.100
 libswscale 8. 1.100 / 8. 3.100
 libswresample 5. 1.100 / 5. 3.100
Input #0, mp3, from 'D:\music\test.mp3':
 Metadata:
 encoder : Lavf58.76.100
 Duration: 00:05:00.12, start: 0.025057, bitrate: 128 kb/s
 Stream #0:0: Audio: mp3 (mp3float), 44100 Hz, stereo, fltp, 128 kb/s
 Metadata:
 encoder : Lavc58.13


Why is
av_dump_formatnot correctly showing stream information ? How can I fix it ?

-
avformat/riff : map Y416 fourcc to RAWVIDEO decoder
23 octobre 2024, par James Almeravformat/riff : map Y416 fourcc to RAWVIDEO decoder
As defined in https://learn.microsoft.com/en-us/windows/win32/medfound/10-bit-and-16-bit-yuv-video-formats#422-formats
Signed-off-by : James Almer <jamrial@gmail.com>
- [DH] libavcodec/raw.c
- [DH] libavformat/riff.c
- [DH] tests/ref/fate/filter-pixdesc-xv48le
- [DH] tests/ref/fate/filter-pixfmts-copy
- [DH] tests/ref/fate/filter-pixfmts-crop
- [DH] tests/ref/fate/filter-pixfmts-field
- [DH] tests/ref/fate/filter-pixfmts-fieldorder
- [DH] tests/ref/fate/filter-pixfmts-hflip
- [DH] tests/ref/fate/filter-pixfmts-il
- [DH] tests/ref/fate/filter-pixfmts-null
- [DH] tests/ref/fate/filter-pixfmts-scale
- [DH] tests/ref/fate/filter-pixfmts-transpose
- [DH] tests/ref/fate/filter-pixfmts-vflip
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