I had similar problem when had to upload file and send user token info at the same time. transformRequest along with forming FormData helped:

        $http({
            method: 'POST',
            url: '/upload-file',
            headers: {
                'Content-Type': 'multipart/form-data'
            },
            data: {
                email: Utils.getUserInfo().email,
                token: Utils.getUserInfo().token,
                upload: $scope.file
            },
            transformRequest: function (data, headersGetter) {
                var formData = new FormData();
                angular.forEach(data, function (value, key) {
                    formData.append(key, value);
                });

                var headers = headersGetter();
                delete headers['Content-Type'];

                return formData;
            }
        })
        .success(function (data) {

        })
        .error(function (data, status) {

        });

For getting file $scope.file I used custom directive:

app.directive('file', function () {
    return {
        scope: {
            file: '='
        },
        link: function (scope, el, attrs) {
            el.bind('change', function (event) {
                var file = event.target.files[0];
                scope.file = file ? file : undefined;
                scope.$apply();
            });
        }
    };
});

Html:

<input type="file" file="file" required />

I was unable to get Pavel's answer working as in when posting to a Web.Api application.

The issue appears to be with the deleting of the headers.

headersGetter();
delete headers['Content-Type'];

In order to ensure the browsers was allowed to default the Content-Type along with the boundary parameter, I needed to set the Content-Type to undefined. Using Pavel's example the boundary was never being set resulting in a 400 HTTP exception.

The key was to remove the code deleting the headers shown above and to set the headers content type to null manually. Thus allowing the browser to set the properties.

headers: {'Content-Type': undefined}

Here is a full example.

$scope.Submit = form => {
                $http({
                    method: 'POST',
                    url: 'api/FileTest',
                    headers: {'Content-Type': undefined},
                    data: {
                        FullName: $scope.FullName,
                        Email: $scope.Email,
                        File1: $scope.file
                    },
                    transformRequest: function (data, headersGetter) {
                        var formData = new FormData();
                        angular.forEach(data, function (value, key) {
                            formData.append(key, value);
                        });
                        return formData;
                    }
                })
                .success(function (data) {

                })
                .error(function (data, status) {

                });

                return false;
            }

Please, have a look on my implementation. You can wrap the following function into a service:

function(file, url) {
  var fd = new FormData();

  fd.append('file', file);

  return $http.post(url, fd, {
    transformRequest: angular.identity,
    headers: { 'Content-Type': undefined }
  });
}

Please notice, that file argument is a Blob. If you have base64 version of a file - it can be easily changed to Blob like so:

fetch(base64).then(function(response) {
  return response.blob(); 
}).then(console.info).catch(console.error);

You can also upload using HTML5. You can use this AJAX uploader.

The JS code is basically:

  $scope.doPhotoUpload = function () {
    // ..
    var myUploader = new uploader(document.getElementById('file_upload_element_id'), options);
    myUploader.send();
    // ..
  }

Which reads from an HTML input element

<input id="file_upload_element_id" type="file" onchange="angular.element(this).scope().doPhotoUpload()">

here is my solution:

// Controller
$scope.uploadImg = function( files ) {
  $scope.data.avatar = files[0];
}

$scope.update = function() {
  var formData = new FormData();
  formData.append('desc', data.desc);
  formData.append('avatar', data.avatar);
  SomeService.upload( formData );
}


// Service
upload: function( formData ) {
  var deferred = $q.defer();
  var url = "/upload"	;
  
  var request = {
    "url": url,
    "method": "POST",
    "data": formData,
    "headers": {
      'Content-Type' : undefined // important
    }
  };

  console.log(request);

  $http(request).success(function(data){
    deferred.resolve(data);
  }).error(function(error){
    deferred.reject(error);
  });
  return deferred.promise;
}


// backend use express and multer
// a part of the code
var multer = require('multer');
var storage = multer.diskStorage({
  destination: function (req, file, cb) {
    cb(null, '../public/img')
  },
  filename: function (req, file, cb) {
    cb(null, file.fieldname + '-' + Date.now() + '.jpg');
  }
})

var upload = multer({ storage: storage })
app.post('/upload', upload.single('avatar'), function(req, res, next) {
  // do something
  console.log(req.body);
  res.send(req.body);
});

<div>
  <input type="file" accept="image/*" onchange="angular.element( this ).scope().uploadImg( this.files )">
  <textarea ng-model="data.desc" />
  <button type="button" ng-click="update()">Update</button>
</div>

There are other solutions you can look into as discussed here file uploader integration for angularjs

In my solution, i have

$scope.uploadVideo = function(){
    var uploadUrl = "/api/uploadEvent";


    //obj with data, that can be one input or form
    file = $scope.video;
    var fd = new FormData();


    //check file form on being
    for (var obj in file) {
        if (file[obj] || file[obj] == 0) {
            fd.append(obj, file[obj]);
        }
    }

    //open XHR request
    var xhr = new XMLHttpRequest();


    // $apply to rendering progress bar for any chunking update
    xhr.upload.onprogress = function(event) {
        $scope.uploadStatus = {
            loaded: event.loaded,
            total:  event.total
        };
        $scope.$apply();
    };

    xhr.onload = xhr.onerror = function(e) {
        if (this.status == 200 || this.status == 201) {

            //sucess

            $scope.uploadStatus = {
                loaded: 0,
                total:  0
            };


            //this is for my solution
            $scope.video = {};
            $scope.vm.model.push(JSON.parse(e.currentTarget.response));
            $scope.$apply();

        } else {
           //on else status
        }
    };

    xhr.open("POST", uploadUrl, true);

    //token for upload, thit for my solution
    xhr.setRequestHeader("Authorization", "JWT " + window.localStorage.token);


    //send
    xhr.send(fd); 
};

}