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• avformat/sccdec : Don't use uninitialized data, fix crash, simplify logic

  1er octobre 2021, par Andreas Rheinhardt

  avformat/sccdec : Don't use uninitialized data, fix crash, simplify logic
  Up until now, the scc demuxer not only read the line that it intends
  
  to process, but also the next line, in order to be able to calculate
  
  the duration of the current line. This approach leads to unnecessary
  
  complexity and also to bugs : For the last line, the timing of the
  
  next subtitle is not only logically indeterminate, but also
  
  uninitialized and the same applies to the duration of the last packet
  
  derived from it.* Worse yet, in case of e.g. an empty file, it is not
  
  only the duration that is uninitialized, but the whole timing as well
  
  as the line buffer itself.** The latter is used in av_strtok(), which
  
  could lead to crashes. Furthermore, the current code always outputs
  
  at least one packet, even for empty files.
  This commit fixes all of this : It stops using two lines at a time ;
  
  instead only the current line is dealt with and in case there is
  
  a packet after that, the duration of the last packet is fixed up
  
  after having already parsed it ; consequently the duration of the
  
  last packet is left in its default state (meaning "unknown/up until
  
  the next subtitle"). If no further line could be read, processing
  
  is stopped ; in particular, no packet is output for an empty file.
  * : Due to stack reuse it seems to be zero quite often ; for the same
  
  reason Valgrind does not report any errors for a normal input file.
  
  ** : While ff_subtitles_read_line() claims to always zero-terminate
  
  the buffer like snprintf(), it doesn't do so if it didn't read anything.
  
  And even if it did, it would not necessarily help here : The current
  
  code jumps over 12 bytes that it deems to have read even when it
  
  hasn't.
  Reviewed-by : Paul B Mahol <onemda@gmail.com>
  
  Signed-off-by : Andreas Rheinhardt <andreas.rheinhardt@outlook.com>
  

  • [DH] libavformat/sccdec.c

• Problem in access "libavcodec/avcodec.h" in CPP [duplicate]

  14 septembre 2021, par Sujay

  Note : Not full working code but part of the code.
Problem is when trying to compile it shows the below output.
FFMPEG have installed.
No flag in VS code but error occurred on compile time.
Thanks in Advance.

  


  #include<bits></bits>stdc&#x2B;&#x2B;.h>&#xA;#include<opencv2></opencv2>opencv.hpp>&#xA;&#xA;extern "C" {&#xA;    #include "libavcodec/avcodec.h"&#xA;    #include "libavformat/avformat.h"&#xA;    #include "libavutil/mathematics.h"&#xA;    #include "libavutil/pixfmt.h"&#xA;    #include "libswscale/swscale.h"&#xA;}&#xA;&#xA;using namespace std;&#xA;using namespace cv;&#xA;&#xA;int main(){&#xA;&#xA;&#xA;&#xA;    AVPacket avpkt; int err, frame_decoded = 0;&#xA;    AVCodec *codec = avcodec_find_decoder ( AV_CODEC_ID_H264 );&#xA;    AVCodecContext *codecCtx = avcodec_alloc_context3 ( codec );&#xA;    avcodec_open2 ( codecCtx, codec, NULL );&#xA;    // Set avpkt data and size here&#xA;    // err = avcodec_decode_video2 ( codecCtx, avframe, &amp;frame_decoded, &amp;avpkt );&#xA;    return EXIT_SUCCESS;&#xA;}&#xA;&#xA;

  


  Output :

  


  h264.cpp:(.text+0x15): undefined reference to `avcodec_find_decoder'
h264.cpp:(.text+0x25): undefined reference to `avcodec_alloc_context3'
h264.cpp:(.text+0x41): undefined reference to `avcodec_open2'
collect2: error: ld returned 1 exit status 


  


• How to "stream" images to ffmpeg to construct a video in .NET 6

  13 septembre 2021, par alkasel

  I'm using FFMPEG command line tool to create a video. As of now I retrive images from memory, but I'd like to avoid writing them to memory in first place and feed FFMPEG directly from memory.

  


  I tried accord-framework.net and it works very well, but now I've switched to .NET 6 and it is not supported (the functionality I used is based on AForge.Video.FFMPEG, an archived project not supporting recent frameworks).

  


  Now as I understand it is possible to have FFMPEG to work on streams instead of images saved on disk. In this post there is a very nice example of doing it in Python.

  


  However I don't know how to do this on .NET 6 using System.Diagnostics.Process : From this post I undestand that I could have FFMPEG take images from standard input using the syntax

  


  -i -


  


  The problem is that I cannot write on standard input before the System.IO.Process (cmd.exe ... \C ffmpeg.exe .... ) has started (I get System.InvalidOperationException : "StandardIn has not been redirected"). However, as soon as such process start, since it find standard input empty, it ends immediately, so I cannot make it in time to fill standard input.

  


  My code looks like this :

  


          MemoryStream memStream = new MemoryStream();

        // Data acquisition
        [...]
        bitmap.Save(memStream, System.Drawing.Imaging.ImageFormat.Bmp);
        [...]

        string ffmpegArgument = "/C ffmpeg.exe -y -i - -c:v libx264 -crf 12 -pix_fmt yuv420p -c:a libvo_aacenc -b:a 128k [...];

        Process cmd = new Process();
        cmd.StartInfo.FileName = "cmd.exe";
        cmd.StartInfo.Arguments = ffmpegArgument;
        cmd.StartInfo.UseShellExecute = false;
        cmd.StartInfo.RedirectStandardInput = true;
        cmd.Start();
        cmd.StandardInput.Write(memStream);


  


  Thanks to everyone who will answer.