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• FFMPEG MKV -> MP4 Batch Conversion

  15 juillet 2024, par blaziken386

  I'm trying to write a program that lets me convert a series of .mkv files with subtitle files into .mp4 files with the subs hardcoded.

  


  Right now, the script I use is

  


  ffmpeg -i input.mkv -vf subtitles=input.mkv output.mp4



  


  This is fine, but it means I can only convert them one at a time, and it's kind of a hassle because it means I have to fiddle with it every few minutes to set up the next one.

  


  I have another script I use for converting .flac files to .mp3 files, which is

  


  @ECHO OFF

FOR %%f IN (*.flac) DO (
echo Converting: %%f
ffmpeg -i "%%f" -ab 320k -map_metadata 0 "%%~nf.mp3"
)

echo Finished

PAUSE



  


  Running that converts every single .flac folder into an .mp3 equivalent, with the same filename and everything.

  


  I've tried to combine the above scripts into something like this :

  


  @ECHO OFF

FOR %%f IN (*.mkv) DO (
echo Converting: %%f
ffmpeg -i "%%f" -vf subtitles=%%f "%%~nf.mp4"
)

echo Finished

PAUSE


  


  but every time I do so, it returns errors like "invalid argument" or "unable to find a suitable output type", or "error initializing filters", or "2 frames left in the queue on closing" or something along those lines. I've swapped out subtitles=%%f for "subtitles-%%f" or subtitles="%%f.mkv" and so on and so forth, and none of those give me what I want either. Sometimes it creates Empty .mp4 file containers with nothing in them, sometimes it does nothing at all.

  


  I don't really understand what exactly is happening under the hood in that flac->mp3 code, because I grabbed it from a different stackoverflow post years ago. All I know is that trying to copy that code and repurpose it into something else doesn't work. Is this just an issue where I've fucked up the formatting of the code and not realized it, or is this a "ffmpeg can't actually do that because of a weird technical issue" thing ?

  


  I also tried the code listed here, when Stackoverflow listed that as a possible duplicate, but that gave me similar errors, and I don't really understand why !

  


  Also, if it's relevant, I'm running windows.

  


• How are ARM GPUs supported by Video display/decoding/encoding Programs ?

  7 juillet 2020, par John Allard

  I often see ARM-based chips advertising onboard GPUs, like the RPI3 that came with "Broadcom VideoCore IV @ 250 MHz" and the OdroidC2 that comes with a "Mali-450 GPU". These chips advertise stuff like "Decode 4k/30FPS, Encode 1080p,30FPS" as the capabilities of the GPU for encoding and decoding videos.

  


  My question is this - how does a program like Kodi, VLC, or FFMPEG come to make use of these GPUs for actual encoding and decoding ? When I do research on how to make use of the Mali-450 GPU, for example, I find some esoteric and poorly documented C-examples of sending compressed frames to the GPU and getting decoded frames back. If I were to use a device like the OdroidC2 and install VLC on it, how does VLC make use of the GPU ? Did someone have to write logic into VLC to use the specific encoding/decoding API exposed by the Mali GPU in order to use it or do these GPUs follow some sort of consistent API that is exposed by all GPUs and VLC/Kodi can just program against this system API ?

  


  The reason I ask this question is that VLC and Kodi tend to support these GPUs out of the Box, but a very popular program like FFMPEG that prides itself on supporting as many codecs and accelerators as possible has no support for decoding and encoding with the Mali GPU series. Why would VLC/Kodi support encoding/decoding and not FFMPEG ? Why do these manufacturers claim wild decoding and encoding support if these GPUs are difficult to program against and one must use their custom esoteric APIs instead of something like libavcodec ?

  


  I hope my question makes sense, I guess what I'm curious about is that GPUs on most systems whether it be the Intel HD Graphics, Nvidia cards, AMD cards, etc seem to be used automatically by most video players but when it comes to using something like FFMPEG against these devices the process becomes much more process and you need to custom compile the build and give special flags to use the device as intended. Is there something I'm missing here ? Is VLC programmed to make use of all of these different type of GPUs ? And why, in that case, does FFMEPG not support Mali GPUs out of the Box ?

  


• Confused about x264 and encoding video frames

  26 février 2015, par spartygw

  I built a test driver for encoding a series of images I have captured. I am using libx264 and based my driver off of this guy’s answer :

  StackOverflow link

  In my case I am starting out by reading in a JPG image and converting to YUV and passing that same frame over and over in a loop to the x264 encoder.

  My expectation was that since the frame is the same that the output from the encoder would be very small and constant.

  Instead I find that the NAL payload is varied from a few bytes to a few KB and also varies highly depending on the frame rate I specify in the encoder parameters.

  Obviously I don’t understand video encoding. Why does the output size vary so much ?

  int main() 
  
  {
  
    Image image(WIDTH, HEIGHT);
  
    image.FromJpeg("frame-1.jpg");
  
  
  
    unsigned char *data = image.GetRGB();
  
  
  
    x264_param_t param;
  
  
  
    x264_param_default_preset(&param, "fast", "zerolatency");
  
    param.i_threads = 1;
  
    param.i_width = WIDTH;
  
    param.i_height = HEIGHT;
  
    param.i_fps_num = FPS;
  
    param.i_fps_den = 1;
  
  
  
    // Intra refres:
  
    param.i_keyint_max = FPS;
  
    param.b_intra_refresh = 1;
  
  
  
    //Rate control:
  
    param.rc.i_rc_method = X264_RC_CRF;
  
    param.rc.f_rf_constant = FPS-5;
  
    param.rc.f_rf_constant_max = FPS+5;
  
  
  
    //For streaming:
  
    param.b_repeat_headers = 1;
  
    param.b_annexb = 1;
  
  
  
    x264_param_apply_profile(&param, "baseline");
  
  
  
    // initialize the encoder
  
    x264_t* encoder = x264_encoder_open(&param);
  
    x264_picture_t pic_in, pic_out;
  
    x264_picture_alloc(&pic_in, X264_CSP_I420, WIDTH, HEIGHT);
  
    // X264 expects YUV420P data use libswscale 
  
    // (from ffmpeg) to convert images to the right format
  
    struct SwsContext* convertCtx =
  
          sws_getContext(WIDTH, HEIGHT, PIX_FMT_RGB24, WIDTH, HEIGHT,
  
                         PIX_FMT_YUV420P, SWS_FAST_BILINEAR,
  
                         NULL, NULL, NULL);
  
  
  
    // encoding is as simple as this then, for each frame do:
  
    // data is a pointer to your RGB structure
  
    int srcstride = WIDTH*3; //RGB stride is just 3*width
  
    sws_scale(convertCtx, &data, &srcstride, 0, HEIGHT,
  
              pic_in.img.plane, pic_in.img.i_stride);
  
    x264_nal_t* nals;
  
    int i_nals;
  
    int frame_size =
  
          x264_encoder_encode(encoder, &nals, &i_nals, &pic_in, &pic_out);
  
  
  
    int max_loop=15;
  
    int this_loop=1;
  
  
  
    while (frame_size >= 0 && --max_loop)
  
    {
  
        cout << "------------" << this_loop++ << "-----------------\n";
  
        cout << "Frame size = " << frame_size << endl;
  
        cout << "output has " << pic_out.img.i_csp << " colorspace\n";
  
        cout << "output has " << pic_out.img.i_plane << " # img planes\n";
  
  
  
        cout << "i_nals = " << i_nals << endl;
  
        for (int n=0; n