how to read header-chunks from a CAF-file using co

问题:

i'm trying to read a CAF-file on OSX, using AudioToolbox's Extended Audio File API.

opening the file works fine, however, i need to access the UUID chunk, and i cannot find any reference on how to do that (or how to access any header-chunk of the file)

surely there must be a way to do this without parsing the file on my own.

PS: i can already do this with libsndfile, but i want to find a way to do this with only components that come with OSX.

i already tried calling ExtAudioFileGetProperty() with the ExtAudioFilePropertyID set to 'uuid' but this doesn't seem to work.

回答1:

it turned out that the trick is not to use the ExtAudio API for accessing low-level functionality like the UUID chunk. (if you need to access the file via ExtAudio API, it's possible to create an ExtAudioHandle from an AudioFileID.)

in the end i used something like this:

AudioFileID fileID;
ExtAudioFileRef extFile;

OSStatus err = AudioFileOpenURL((CFURLRef)inURL, kAudioFileReadPermission, 0, &fileID);
if(noErr!=err)return;
err = ExtAudioFileWrapAudioFileID (fileID, false, &extFile); // in case we *also* want to access the file via ExtAudio
if(noErr!=err)return;

for(index=0; ; index++) {
  UInt32 size=0;
  char*data=NULL;

  OSStatus err = AudioFileGetUserDataSize (fileID,'uuid',index,&size);
  if(noErr!=err)break;   // check whether we were able to read the chunksize
  if(0==size)continue;    // check whether there is some payload in the uuid chunk

  data=calloc(size, 1);
  if(!data)continue;
  err = AudioFileGetUserData (fileID, 'uuid', index, &size, data);
  if(noErr!=err){free(data); break;}   // check whether we were able to read the chunksize
  /* ... */
  free(data);
}
ExtAudioFileDispose(extFile);
AudioFileClose(fileID);