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• Wave64 (.w64) file format : question regarding chunk GUIDs

  24 janvier 2023, par pdu

  I am having trouble understanding the headers of the Wave64 (.w64) files generated by ffmpeg and especially the GUIDs.

  


  The specification

  


  I have found this document which describes the file format and the GUIDs. I have also found other websites (here and here) that (indirectly) point to the same document. So this document is the only thing I have.

  


  According to this document the GUIDs are 128bits/16bytes long and should start with the FourCC of the Wave file format, but in lowercase instead of uppercase (see page 3). It also says that the 64bits fields are stored in little-endian (see item 3 of the list page 1), but it does not say anything about 128bits fields (but it should be the same).
For example the GUID for the RIFF chunk is : 66666972-912E-11CF-A5D6-28DB04C10000.

  


  The problem

  


  When I open a .w64 file generated by ffmpeg with an hex editor, I get this : 72 69 66 66 2E 91 CF 11 A5 D6 28 DB 04 C1 00 00. At the beginning, 76 69 66 66 stands for riff in ASCII. We can see that 0x66666972 from the spec was indeed stored in little-endian order (so far, so good). If we continue, we have 2E 91 and CF 11, which are still little-endian for 0x912E and 0x11CF. But now it gets weird : the following group of bytes are : A5 D6 and 28 DB 04 C1 00 00 for 0xA5D6 and 0x28DB04C10000 in the spec. So it is in big-endian now ?

  


  For reference, the relevant ffmpeg source files are wavenc.c, w64.h and w64.c.
I have also found this thread where someone implemented a .wav to .w64 converter (see the .7z attachment in the first post) and the GUIDs are stored in the same way as ffmpeg.

  


  Conclusion

  


  Seeing that two different implementations are doing the same thing, it probably means that I am missing something. Do you have any explanation ?

  


• Big question of Target size, or video bitrate must be specified when using two-pass

  14 juillet 2022, par Rojojun

  I tried to solve the error which is Target size, or video bitrate must be specified when using two-pass.

  


  But I couldn't find how to solve it and how to find path of video exactly I attached my code below this post

  


  Please give me some tips of solving the problem !

  


  @Service
public class ThumbnailService {

    public HashMap exportThumbnail(File file) throws Exception {
        // file is from controller and form-data
        //String inputPath = "Users/hojunna/Download/my/";
        //String outputPath = "/usr/local/video/thumbnail/";

        String ffmpegBasePath = "/opt/homebrew/bin/";
        FFmpeg ffmpeg = new FFmpeg(ffmpegBasePath+"ffmpeg");        
        FFprobe ffprobe = new FFprobe(ffmpegBasePath+"ffprobe");    
        
        FFmpegBuilder builder = new FFmpegBuilder()
                .setInput("/Users/hojunna/Desktop/" + file)                         
                //.overrideOutputFiles(true)                    
                //.addExtraArgs("-ss", "00:00:01")          
                .addOutput("/Users/hojunna/Desktop/test.jpg")       
                .setFrames(1)
                .setVideoFilter("select='gte(n\\,10)',scale=200:-1")
                .done();

        FFmpegExecutor executor = new FFmpegExecutor(ffmpeg, ffprobe);      
        executor.createJob(builder).run();                                  
        executor.createTwoPassJob(builder).run();                           

        HashMap resultMap = new HashMap();
        return resultMap;
    }
}


  


• How can I tell subprocess to answer "y" to a commandline question ?

  13 mai 2022, par Faindirnomainzein

  I'm automating an ffmpeg command but when the file exists already, it asks me if I have to "Overwrite [y/N]" and it stalls the entire script until I have to enter "y" myself in the console. How can I automate that ?

  


  for file in all_files_in_dir:
    output = file.split('.')[0]
    subprocess.call(f'ffmpeg -hide_banner -i {file} -map 0:s:1 {output}.srt')


  


  I have to enter "y" myself (as seen in green), then press enter everytime a file is already found. The answer will be "y", so I can hardcode the answer "y" if need be.