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• Sending frames from memory to FFMPEG command line program .NET 6

  15 septembre 2021, par Alessandro Martinelli

  I'm trying to use the pipe to send frames generated by my program to ffmpeg command line utility without saving them on disk. Please note I was able to generate a video by first saving frames on disk as images and then having FFMPEG generate a video from such images, but that approach is worse performance-wise and implies writing more data on SSD.

  


  I could use the help of this post, but I have FFMPEG returning an error on frame size, and I don't know how to solve it.

  


  My code is the following :

  


  //object storing single frame returned from camera
mv.impact.acquire.Request pRequest; 
string outputPath = ...;
List frames = new List();

[...]

// Single frame is saved into memory
MemoryStream stream = new MemoryStream();
using (RequestBitmapData data = pRequest.bitmapData) {
    data.bitmap.Save(stream, System.Drawing.Imaging.ImageFormat.Bmp);
    // Please note that now printing data.bitmap.PixelFormat would return Format24bppRgb
}
frames.Add(stream.ToArray());

[...] 

Console.WriteLine(frames.Count + " frames collected. First one length is " + frames.First().Length);

string ffmpegArgument = "/C " + _ffmpegPath + "\\ffmpeg -y -f rawvideo -pix_fmt rgb24 -framerate 3 -video_size 728x544 -i - -c:v libx264 -preset 9 -c:a libvo_aacenc " + outputPath;

Process cmd = new Process();
cmd.StartInfo.FileName = "cmd.exe";
cmd.StartInfo.Arguments = ffmpegArgument;
cmd.StartInfo.UseShellExecute = false;
cmd.StartInfo.RedirectStandardError = false;
cmd.StartInfo.RedirectStandardInput = true;

Console.WriteLine("Executing command " + ffmpegArgument + "...");
cmd.Start();
foreach (byte[] frame in frames) {
        cmd.StandardInput.Write(frame);
}
cmd.StandardInput.Flush();
cmd.StandardInput.Close();


  


  However, when I execute the program, I have the following output :

  


  492 frames collected. First one length is 1188150
Executing command /C ExternalTools\FFmpeg\ffmpeg -y -f rawvideo -pix_fmt rgb24 -framerate 32 -video_size 728x544 -i - -c:v libx264 -preset ultrafast -c:a libvo_aacenc -b:a 128k "Output\TemporaryVideo\2021-09-13 18_58_58.mp4"...
ffmpeg version 2021-06-27-git-49e3a8165c-essentials_build-www.gyan.dev Copyright (c) 2000-2021 the FFmpeg developers
built with gcc 10.3.0 (Rev2, Built by MSYS2 project)

[...] (configurations)

[rawvideo @ 00000241d34feac0] Packet corrupt (stream = 0, dts = 0).
Input #0, rawvideo, from 'pipe:':
  Duration: N/A, start: 0.000000, bitrate: 304152 kb/s
  Stream #0:0: Video: rawvideo (RGB[24] / 0x18424752), rgb24, 728x544, 304152 kb/s, 32 tbr, 32 tbn
Stream mapping:
  Stream #0:0 -> #0:0 (rawvideo (native) -> h264 (libx264))
pipe:: corrupt input packet in stream 0
[rawvideo @ 00000241d3511640] Invalid buffer size, packet size 6396 < expected frame_size 1188096
Error while decoding stream #0:0: Invalid argument

[...] (cpu capabilities)

Output #0, mp4, to 'Output\TemporaryVideo\2021-09-13 18_58_58.mp4':
  Metadata:
    encoder         : Lavf59.3.101
  Stream #0:0: Video: h264 (avc1 / 0x31637661), yuv444p, 728x544, q=2-31, 32 fps, 16384 tbn
    Metadata:
      encoder         : Lavc59.2.100 libx264
    Side data:
      cpb: bitrate max/min/avg: 0/0/0 buffer size: 0 vbv_delay: N/A
frame=    0 fps=0.0 q=0.0 Lsize=       0kB time=00:00:00.00 bitrate=N/A speed=   0x
video:0kB audio:0kB subtitle:0kB other streams:0kB global headers:0kB muxing overhead: unknown
Conversion failed!


  


  The value expected by FFMPEG seems correct (1188096 = 728 x 544 x 3), but I don't understand where FFMPEG gets that "packet size 6396" from. Furthermore, that value (6396) changes at every program execution.

  


  I'm pretty sure frames are not corrupted since, if I save such frames on disk, the image is generated correctly.

  


  Thank you for your time,
Alessandro

  


• FFMPEG Aligning Timestamps in m3u8 Stream

  16 septembre 2021, par maxwellray

  I'm receiving an m3u8 stream with the following structure

  


  #EXTM3U
#EXT-X-VERSION:3
#EXT-X-ALLOW-CACHE:YES
#EXT-X-MEDIA-SEQUENCE:1193
#EXT-X-PROGRAM-DATE-TIME:2021-09-15T22:57:30+00:00
#EXT-X-TARGETDURATION:11
#EXTINF:10.054589,
20210915220000/20210915225710.ts
#EXTINF:10.008855,
20210915220000/20210915225720.ts


  


  Every 10 seconds, the playlist is updated with a new media file path and the oldest media path is removed. Each media file path contains a clip that is approximately 10 seconds long (i.e., over a very long time, the average length of each clip should be 10 seconds). Each media path is timestamped, rounded to 10 seconds.

  


  I run a system where I record continuous 32-minute clips of this stream using ffmpeg, and I need to know the exact timestamp where I start to record and where I stop. I'm encountering a sort of race condition where ffmpeg will start recording at the beginning of the oldest clip in the playlist instead of when it actually gets kicked off. The problem is illustrated below

  


  Clip 1: |==========|
Clip 2:            |==========|
FFMPEG:    |==================| <= ffmpeg is kicked off at t=3
OUTPUT: |=====================| <= but video would actually start at t=0


  


  I'm wondering if there's a way to ensure that the clips I record actually start when ffmpeg is kicked off, not from the start of the earliest clip in the stream.

  


  Thanks !

  


• Link error when compiling opencv from source when including ffmpeg compiled from source

  17 septembre 2021, par Drew

  I've been stuck on this problem for weeks.

  


  I'm trying to build opencv on a raspberry pi 4 with x264 support. To do this I need to include ffmpeg, and also build that from source.

  


  However when compiling opencv, I'm consistently getting these linker errors :

  


  /usr/bin/ld: ../../lib/libopencv_videoio.so.4.5.3: undefined reference to `avcodec_get_context_defaults3'
/usr/bin/ld: ../../lib/libopencv_videoio.so.4.5.3: undefined reference to `av_lockmgr_register'
/usr/bin/ld: ../../lib/libopencv_videoio.so.4.5.3: undefined reference to `av_register_all'


  


  I'm new to Linux, so I'm not exactly sure how to get started troubleshooting this. I believe I have ffmpeg correctly compiled and installed.

  


  Here's the steps I use :

  


  Configure ffmpeg :

  


  sudo ./configure \
--prefix=/usr \
--extra-ldflags="-latomic" \
--enable-shared \
--extra-libs='-lpthread -lm' \
--ld=g++ \
--enable-gpl \
--disable-debug \
--enable-nonfree \
--enable-libx264 \
--enable-omx \
--enable-omx-rpi \
--enable-gnutls \
--enable-libfreetype \
--enable-libmp3lame


  


  Then build it :
sudo make -j4

  


  Then install it as a package : (so opencv cmake will detect it)

  


  sudo checkinstall -y --deldoc=yes --pkgversion=9999 --pkgname=ffmpeg


  


  Then configure opencv (ffmpeg is detected)

  


  sudo cmake ../opencv_sources -D CMAKE_BUILD_TYPE=RELEASE \
-D OPENCV_EXTRA_MODULES_PATH= $PWD/../opencv_contrib/modules \
-D ENABLE_NEON=ON \
-D ENABLE_VFPV3=ON \
-D BUILD_TESTS=ON \
-D INSTALL_PYTHON_EXAMPLES=OFF \
-D OPENCV_ENABLE_NONFREE=ON \
-D CMAKE_SHARED_LINKER_FLAGS='-latomic -L/usr/lib' \
-D WITH_V4L=ON \
-D WITH_QT=OFF \
-D BUILD_EXAMPLES=OFF \
-D CPU_BASELINE=NATIVE \
-D CMAKE_INSTALL_PREFIX="$HOME/opencv_build" \
-D BUILD_opencv_apps=OFF \
-D BUILD_opencv_python2=OFF \
-D BUILD_SHARED_LIBS=ON \
-D WITH_FFMPEG=ON


  


  Then build opencv :

  


  sudo make -j4


  


  And this is where I get linking errors.

  


  I checked in /usr/lib and the .so files appear to be there :

  


  ls /usr/lib | grep libav

libavcodec.a
libavcodec.so
libavcodec.so.59
libavcodec.so.59.4.101
libavdevice.a
libavdevice.so
libavdevice.so.59
libavdevice.so.59.0.100
libavfilter.a
libavfilter.so
libavfilter.so.8
libavfilter.so.8.1.103
libavformat.a
libavformat.so
libavformat.so.59
libavformat.so.59.4.101
libavutil.a
libavutil.so
libavutil.so.57
libavutil.so.57.3.100


  


  How do check where opencv is looking when linking ? And is there a way I can check the shared libraries that ffmpeg generated to make sure they work ?

  


  The ffmpeg version is : git-2021-08-10-c245963

  


  And opencv is 4.5.3-dev