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    14 novembre 2010, par

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  • Support de tous types de médias

    10 avril 2011

    Contrairement à beaucoup de logiciels et autres plate-formes modernes de partage de documents, MediaSPIP a l’ambition de gérer un maximum de formats de documents différents qu’ils soient de type : images (png, gif, jpg, bmp et autres...) ; audio (MP3, Ogg, Wav et autres...) ; vidéo (Avi, MP4, Ogv, mpg, mov, wmv et autres...) ; contenu textuel, code ou autres (open office, microsoft office (tableur, présentation), web (html, css), LaTeX, Google Earth) (...)

Sur d’autres sites (8239)

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

    26 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 ?

    


  • 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 ?

    


  • Should libavcodec handle non-packed/non-byte-aligned mp3 packets ?

    27 août 2015, par Rhythmic Fistman

    I’m transcoding shoutcast streams using libavcodec and I noticed that during the day I get a few 10s’ of packets that it cannot decode without some help :

    1. Leading zero bytes before a packet sync word, e.g. 0x0000fffa

    2. non-byte aligned syncword, e.g 0x82a0fffa

    In the first case I have to toss out the zero bytes and in the second I have to shift the data up by an odd number of nibbles.

    I don’t have a watertight knowledge of the mp3 spec (is there one ?), but my impression was that the packet format was a bit oriented, not byte, so both types of packets look right to me.

    So who is in the wrong here ?

    Is it libavcodec for not parsing valid packets ?

    Or the stream encoder for producing non-standard packets ?

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