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• ffmpeg libswresample channel mapping

  21 mars 2024, par Joseph Katrinka

  Im currently working on some c++ that uses ffmpeg to take audio from a stereo file and make a mono audio file using only the sample from one channel.
I havent been able to find and examples of people using the swr_set_channel_mapping call online, so Im wondering if anyone knows of the correct usage.
Right now Im doing something like this

  


  swr_alloc_set_opts2(&swrCtx, &out_channel_layout, AV_SAMPLE_FMT_S16, codecCtx->sample_rate, &codecCtx->ch_layout, codecCtx->sample_fmt, codecCtx->sample_rate, 0, NULL);

int* channel_mapping = (int*)av_mallocz(2 * sizeof(int));
if (useLeft)
{
channel_mapping[0] = AV_CH_FRONT_LEFT;
}
else
{
channel_mapping[0] = AV_CH_FRONT_RIGHT;
}   
swr_set_channel_mapping(swrCtx, channel_mapping);

if (swr_init(swrCtx) < 0)
    {
        DBG("failed to init resampler");
        ffmpegCleanup();
        return false;
    }



  


  Is this the correct way to do this ? Its been giving me some problems and Im worried I could be doing something wrong.
Thanks.

  


  Ive tried different ways of defining channel_mapping with no success. Im not sure what the correct way is and an example would be pretty useful.

  


• How to install ffmpeg and an app together on a Mac ?

  31 décembre 2020, par Patrick

  I have an electron app built and packaged for macOS in a .app file. The app requires ffmpeg to be installed on the end-user's computer to be used.

  



  Currently, I've had to manually install ffmpeg on each end-user's computer to run the app.

  



  I want to distribute the app online with an easy installer for both ffmpeg and the app. I've seen .dmg files which allows you to drag the .app into the applications folder easily, but the ffmpeg dependency is still absent in the installation process.

  



  How can I install ffmpeg and the app together on a mac ?

  



  Perhaps including the ffmpeg build in the .app content is a solution as well.
This may not be possible though because a relevant question mentions there are only abstractions of the ffmpeg CLI instead of something that can directly use ffmpeg.

  


• youtube-dl download one minute per every 5 minutes (on a twitch video, but i have the local file saved too if easier)

  18 mai 2016, par babadoctor

  I would like to do what the title says

  This is a ffmpeg command to download from a specific time in a video, offline or online.

  ffmpeg -ss (stop time) -i (direct video link) -t (start time) -c:v copy -c:a copy (title.mp4)

  I am going to be downloading this on OSX.
  I dont care what the title is.

  I think* there is a bash command that allows me to change the timings in this command up by a specific amount (+300 seconds per, the counter for start and stop time is in raw seconds)

  So, bash script that runs that command but increases the start and stop times incrementally by 300 (the stop timing being 60+ seconds ahead), downloads, then repeats.