upload.kt

override fun uploadVideo(pathToVideoFile: String) : Observable<ResponseBody>{
        val videoFile = File(pathToVideoFile)

        val videoRequestBody = ProgressEmittingRequestBody(mediaType = "video/*", file = videoFile)
        val vFile = MultipartBody.Part.createFormData("file", videoFile.name, videoRequestBody)

        val bodyMap: HashMap<String, @JvmSuppressWildcards RequestBody> = HashMap()
        val body = responseEntity.multipartRequest.body

        createRequestBodyMap(bodyMap, body)

        val amazonUrl = responseEntity.multipartRequest.url
        val response = uploadApi.uploadVideoToServer(amazonUrl, bodyMap, vFile)

        return response.observeOn(postExecutionThread.scheduler).subscribeOn(backgroundThreadScheduler.scheduler)
    }

    private fun createRequestBodyMap(bodyMap: java.util.HashMap<String, RequestBody>, body: java.util.HashMap<String, String>) {
        for ((k,v) in body){
            bodyMap.put(k,createRequestBody(v))
        }
    }


    private fun createRequestBody(value: String): RequestBody {
        return RequestBody.create(MediaType.parse(MULTIPART_FORM_DATA), value)
    }

    companion object{
       const val MULTIPART_FORM_DATA = "multipart/form-data"
    }