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• How to stream frames from OpenCV C++ code to Video4Linux or ffmpeg ?

  6 juillet 2022, par usamazf

  I am experimenting with OpenCV to process frames from a video stream. The goal is to fetch a frame from a stream, process it and then put the processed frame to a new / fresh stream.

  


  I have been able to successfully read streams using OpenCV video capture functionality. But do not know how I can create an output stream with the processed frames.

  


  In order to do some basic tests, I created a stream from a local video file using ffmpeg like so :

  


  ffmpeg -i sample.mp4 -v 0 -vcodec mpeg4 -f mpegts \
        "udp://@127.0.0.1:23000?overrun_nonfatal=1&fifo_size=50000000"


  


  And in my C++ code using the VideoCapture functionality of the OpenCV library, I am able to capture the above created stream. A basic layout of what I am trying to achieve is attached below :

  


  cv::VideoCapture capture("udp://@127.0.0.1:23000?overrun_nonfatal=1&fifo_size=50000000", cv::CAP_FFMPEG);

cv::Mat frame;

while (true) 
{
    // use the above stream to capture a frame
    capture >> frame;
    
    // process the frame (not relevant here)
    ...

    // finally, after all the processing is done I 
    // want to put this frame on a new stream say at
    // udp://@127.0.0.1:25000, I don't know how to do
    // this, ideally would like to use Video4Linux but
    // solutions with ffmpeg are appreciated as well
}


  


  As you can see from comment in above code, I don't have any idea how I should even begin handling this, I tried searching for similar questions but all I could find was how to do VideoCapture using streams, nothing related to outputting to a stream.

  


  I am relatively new to this and this might seem like a very basic question to many of you, please do excuse me.

  


• ffmpeg batch process issue mac

  22 octobre 2023, par e e

  I'm using ffmpeg to batch process all files(with names containing spaces) in a directory. The script is like :

  


  echo my converter
read -p "Enter give folder: " folder
echo '//////////////////////START CONVERTING FROM FOLDER///////////////////////'

find $folder -type f -name "*[[:space:]]*" | while read file; do
    release="${file%%.*}"'_t.mp4';
    echo "$file";
    ffmpeg -i "$file" -c copy "$release" -loglevel error -stats
    echo $release;
done


  


  the script searches all the files in the address and ffmpeg one by one. However the first file will always fail due to some unknown issues :

  


  [mpegts @ 0x7fb8e9904a40] Continuity check failed for pid 17 expected 2 got 3
[mpegts @ 0x7fb8e9904a40] Continuity check failed for pid 0 expected 0 got 2
[mpegts @ 0x7fb8e9904a40] Continuity check failed for pid 4096 expected 0 got 2
[mpegts @ 0x7fb8e9904a40] Continuity check failed for pid 256 expected 2 got 7
[mpegts @ 0x7fb8e9904a40] Packet corrupt (stream = 0, dts = 203523000).
/Users/xy/Downloads/aaa/aa vv.ts: corrupt input packet in stream 0
[NULL @ 0x7fb8e9905a40] Decoding VUI



  


  If there is only one file, the process works fine.
If comment out the ffmpeg command, it echoes as expected :

  


  /Users/xy/Downloads/aaa/aa vv_t.mp4
/Users/xy/Downloads/aaa/aa vv_t_t.mp4
/Users/xy/Downloads/aaa/aa vv.ts
/Users/xy/Downloads/aaa/aa vv_t.mp4
/Users/xy/Downloads/aaa/cc ee.ts
/Users/xy/Downloads/aaa/cc ee_t.mp4


  


  it first find the target files and then converts into another with different file names.
Any suggestions, thank you !!

  


• Could not find ref with POC ffmpeg H265

  7 juin 2021, par user1307697

  I'm trying to develop a video streaming with H265. Unfortunately, in decoding phase, I have these errors :

  


  [hevc @ 0x5563d05b4940] Could not find ref with POC

  


  and the resulting frames are corrupted.

  


  I cannot understand the meaning of this type of error. How can I fix it ?