iOS - Read/Write XMP metadatas of mp4 videos - ios

Question

I need to read and inject XMP metadatas in an mp4 container.
I know this is possible on android with the "mp4parser" library, but I couldn't find an equivalent for iOS.
For the read part, is it possible to read every footage from the camera roll to inspect their 360 XMP metadatas quickly ?
For the writing, I'm trying to use Adobe's XMP toolkit. I have an mp4 video in a folder, and I want to inject into it some 360 metadatas.
After injecting the metadatas (I suppose it works), I export the video to the camera roll, but it looks like the video is converted to m4v and it lost every metadata I've written. Is it expected, or is my code wrong ?
Here's the code :
MetadataManager.mm
#import "MetadataManager.h"
#define IOS_ENV 1
#include <string>
#define TXMP_STRING_TYPE std::string
#define XMP_INCLUDE_XMPFILES 1
#include "XMP.incl_cpp"
#include "XMP.hpp"
#include <iostream>
#include <fstream>
using namespace std;
#implementation MetadataManager {
}
+ (void)write360Metadatas:(NSString *)filePath {
if (!SXMPMeta::Initialize())
exit(1);
if (!SXMPFiles::Initialize())
exit(1);
SXMPFiles myFile;
XMP_OptionBits opts = kXMPFiles_OpenForUpdate | kXMPFiles_OpenUseSmartHandler;
std::string status = "";
std::string filePathStd = std::string([filePath UTF8String]);
// First, try to open the file
bool ok = myFile.OpenFile(filePathStd, kXMP_UnknownFile, opts);
if( ! ok ){
status += "No smart handler available for " + filePathStd + "\n";
status += "Trying packet scanning.\n";
// Now try using packet scanning
opts = kXMPFiles_OpenForUpdate | kXMPFiles_OpenUsePacketScanning;
ok = myFile.OpenFile(filePathStd, kXMP_UnknownFile, opts);
}
if(ok){
SXMPMeta meta;
myFile.GetXMP( &meta );
displayPropertyValues(&meta);
injectMetadatas(&meta);
// Check we can put the XMP packet back into the file
if(myFile.CanPutXMP(meta))
{
// If so then update the file with the modified XMP
myFile.PutXMP(meta);
}
// Close the SXMPFile. This *must* be called. The XMP is not
// actually written and the disk file is not closed until this call is made.
myFile.CloseFile();
}
}
SXMPMeta createXMPFromRDF()
{
const char * rdf =
"<rdf:SphericalVideo xmlns:rdf='http://www.w3.org/1999/02/22-rdf-syntax-ns#'"
" xmlns:GSpherical='http://ns.google.com/videos/1.0/spherical/'>"
"<GSpherical:Spherical>true</GSpherical:Spherical>"
"<GSpherical:Stitched>true</GSpherical:Stitched>"
"<GSpherical:StitchingSoftware>Spherical Metadata Tool</GSpherical:StitchingSoftware>"
"<GSpherical:ProjectionType>equirectangular</GSpherical:ProjectionType>"
"</rdf:SphericalVideo>";
SXMPMeta meta;
// Loop over the rdf string and create the XMP object
// 10 characters at a time
int i;
for (i = 0; i < (long)strlen(rdf) - 10; i += 10 )
{
meta.ParseFromBuffer ( &rdf[i], 10, kXMP_ParseMoreBuffers );
}
// The last call has no kXMP_ParseMoreBuffers options, signifying
// this is the last input buffer
meta.ParseFromBuffer ( &rdf[i], (XMP_StringLen) strlen(rdf) - i );
return meta;
}
void injectMetadatas(SXMPMeta * meta)
{
// Add an item onto the dc:creator array
// Note the options used, kXMP_PropArrayIsOrdered, if the array does not exist it will be created
meta->AppendArrayItem(kXMP_NS_DC, "creator", kXMP_PropArrayIsOrdered, "Author Name", 0);
meta->AppendArrayItem(kXMP_NS_DC, "creator", kXMP_PropArrayIsOrdered, "Another Author Name", 0);
// Now update alt-text properties
meta->SetLocalizedText(kXMP_NS_DC, "title", "en", "en-US", "An English title");
meta->SetLocalizedText(kXMP_NS_DC, "title", "fr", "fr-FR", "Un titre Francais");
// Display the properties again to show changes
cout << "After update:" << endl;
displayPropertyValues(meta);
// Create a new XMP object from an RDF string
SXMPMeta rdfMeta = createXMPFromRDF();
// Append the newly created properties onto the original XMP object
// This will:
// a) Add ANY new TOP LEVEL properties in the source (rdfMeta) to the destination (meta)
// b) Replace any top level properties in the source with the matching properties from the destination
SXMPUtils::ApplyTemplate(meta, rdfMeta, kXMPTemplate_AddNewProperties | kXMPTemplate_ReplaceExistingProperties | kXMPTemplate_IncludeInternalProperties);
// Display the properties again to show changes
cout << "After Appending Properties:" << endl;
displayPropertyValues(meta);
}
void displayPropertyValues(SXMPMeta * meta)
{
// Read a simple property
string simpleValue; //Stores the value for the property
meta->GetProperty(kXMP_NS_XMP, "CreatorTool", &simpleValue, 0);
cout << "meta:CreatorTool = " << simpleValue << endl;
// Get the first and second element in the dc:creator array
string elementValue;
meta->GetArrayItem(kXMP_NS_DC, "creator", 1, &elementValue, 0);
if(elementValue != "")
{
cout << "dc:creator[1] = " << elementValue << endl;
meta->GetArrayItem(kXMP_NS_DC, "creator", 2, &elementValue, 0);
cout << "dc:creator[2] = " << elementValue << endl;
}
// Get the the entire dc:subject array
string propValue;
int arrSize = meta->CountArrayItems(kXMP_NS_DC, "subject");
for(int i = 1; i <= arrSize;i++)
{
meta->GetArrayItem(kXMP_NS_DC, "subject", i, &propValue, 0);
cout << "dc:subject[" << i << "] = " << propValue << endl;
}
// Get the dc:title for English and French
string itemValue;
string actualLang;
meta->GetLocalizedText(kXMP_NS_DC, "title", "en", "en-US", 0, &itemValue, 0);
cout << "dc:title in English = " << itemValue << endl;
meta->GetLocalizedText(kXMP_NS_DC, "title", "fr", "fr-FR", 0, &itemValue, 0);
cout << "dc:title in French = " << itemValue << endl;
// Get dc:MetadataDate
XMP_DateTime myDate;
if(meta->GetProperty_Date(kXMP_NS_XMP, "MetadataDate", &myDate, 0))
{
// Convert the date struct into a convenient string and display it
string myDateStr;
SXMPUtils::ConvertFromDate(myDate, &myDateStr);
cout << "meta:MetadataDate = " << myDateStr << endl;
}
cout << "----------------------------------------" << endl;
}
#end
Any help would be appreciated, thanks.

Answer 1

I've finally succeeded, using the c++ port of "spatial-media" instead of Adobe's xmp toolkit.
spatial-media (github repository)