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• ffmpeg/libav easy way to set options for muxer, codec, format, etc [closed]

  14 mars 2023, par Patrick

  Edit (shorter question) :

  


  In the ff tools (e.g. ffplay) I can set all kinds of options by simply providing a list of arguments in cmd. Id like to do that programmatically as well and without having to look up where it belongs and insert it in the different AVDictionary by hand every time. Is there a way to do this easily ?

  


  Long question :

  


  I recently messed around with ffplay code to see how it works and I noticed it uses a very straight forward way to parse and set all the command line options using the library internal cmdutils.h. I personally find the av_opt_set used in other examples of av wrappers quite confusing (Some args are explicitly stored in the struct, some in priv_data ? Im allowed/supposed to modify void*priv_data ? Which objects can I use av_opt_set on ? Which args go in which object and are they declared or in priv_data ? Where is this documented ?).
In ffplay all args are simply stored in an array and distributed to the right codec/muxer/format instance using cmdutil.
Id like to have exactly this functionality for my program (so that i can simply read a json config and don't need to care about it any further). Apparently the necessary OptionDef arrays are already defined in different implementation files.

  


  However my actual question : I noticed the OptionDef array definition in ffplay does not contain all options (only some from cmdutil included via macro). But other options e.g. fflags are not included anywhere (only defined somewhere else) and yet they work. So how does cmdutil set/parse them ?

  


  I hope someone can answer this, since simply adapting cmdutil would be a quite simple solution for me. Id also really appreciate some general guidance regarding my previous questions.

  


  Many Thanks in advance !

  


  I tried looking into the ffmpeg source and expected all OptionDef array definitions to be connected/collected inside a single array such that cmdutil can parse them easily. However this isn't the case and still some cmd options work. Therefore Im confused on how cmtutil is able to parse them

  


• lavf : Use wchar functions for filenames on windows for mkdir/rmdir/rename/unlink

  17 novembre 2014, par Martin Storsjö

  lavf : Use wchar functions for filenames on windows for mkdir/rmdir/rename/unlink
  This makes sure that the internal utf8 path names are handled
  
  properly - the normal file handling functions assume path names
  
  are in the native codepage, which isn’t utf8.
  This assumes that the tools outside of lavf don’t use the mkdir
  
  definition. (The tools don’t do the same reading of command line
  
  parameters as wchar either - they probably won’t handle all possible
  
  unicode file parameters properly, but at least work more predictably
  
  if no utf8/wchar conversion is involved.)
  This is moved further down in os_support.h, since windows.h shouldn’t
  
  be included before winsock2.h, while io.h needs to be included before
  
  the manual defines for lseek functions.
  Signed-off-by : Martin Storsjö <martin@martin.st>
  

  • [DH] libavformat/internal.h
  • [DH] libavformat/os_support.h

• FFMPEG Can't Display The Duration Of a Video

  30 août 2021, par Malkavian

  I'm trying to use ffmpeg to capture frames from a video file, but I can't even get the duration of a video. everytime when I try to access it with pFormatCtx->duration I'm getting 0. I know the pointer initialized and contains the correct duration because if I use av_dump_format(pFormatCtx, 0, videoName, 0); then I actually get the duration data along with other information about the video.
This is what I get when I use av_dump_format(pFormatCtx, 0, videoName, 0); :

  


  Input #0, avi, from 'futurama.avi':
Duration: 00:21:36.28, start: 0.000000, bitrate: 1135 kb/s
Stream #0.0: Video: mpeg4 (Advanced Simple Profile), yuv420p, 512x384
[PAR 1:1 DAR 4:3], 25 tbr, 25 tbn, 25 tbc
Stream #0.1: Audio: ac3, 48000 Hz, stereo, s16, 192 kb/s 


  


  I don't understand why av_dump_format can display duration and I can't. I checked the function definition, to display the duration, the function also uses pFormatCtx->duration. It's not just the duration other member variables also don't display the proper data when I call them in main.cpp

  


  Here's my code :

  


  extern "C" {&#xA;    #include<libavcodec></libavcodec>avcodec.h>&#xA;    #include<libavformat></libavformat>avformat.h>&#xA;    #include<libswscale></libswscale>swscale.h>&#xA;}&#xA;&#xA;int main(int argc, char *argv[]) {&#xA;    AVFormatContext *pFormatCtx = NULL;&#xA;&#xA;    const char videoName[] = "futurama.avi";&#xA;&#xA;    // Register all formats and codecs.&#xA;    av_register_all();&#xA;    cout &lt;&lt; "Opening the video file";&#xA;    // Open video file&#xA;    int ret = avformat_open_input(&amp;pFormatCtx, videoName, NULL, NULL) != 0;&#xA;    if (ret != 0) {&#xA;        cout &lt;&lt; "Couldn&#x27;t open the video file." &lt;&lt; ret ;&#xA;        return -1;&#xA;    }&#xA;    if(avformat_find_stream_info(pFormatCtx, 0) &lt; 0) {&#xA;        cout &lt;&lt; "problem with stream info";&#xA;        return -1;&#xA;    }&#xA;&#xA;    av_dump_format(pFormatCtx, 0, videoName, 0);&#xA;    cout &lt;&lt; pFormatCtx->bit_rate &lt;&lt; endl; // different value each time, not initialized properly.&#xA;    cout &lt;&lt; pFormatCtx->duration &lt;&lt; endl; // 0&#xA;    return 0;&#xA;}&#xA;

  


  I don't know if it helps but, I use QtCreator on Ubuntu and linked the libraries statically.