​public static String upload(String folderId, String documentId, String fileName, String base64BlobValue) {
        if(documentId == '' || documentId == null) {
            Document document = new Document(Name=fileName, FolderId=folderId, Body=EncodingUtil.Base64Decode(base64BlobValue), IsPublic=true);
            insert document;

            return document.Id;

        } else {

            Document document = [select Id, Body from Document where Id = :documentId];
            update new Document(Id = documentId, Body = EncodingUtil.Base64Decode(EncodingUtil.Base64Encode(document.Body) + base64BlobValue));

            return documentId;
        }
    }

Hi,
I'm trying to upload files (image/audio/video) to FeedItem in chunks, the above example shows how I'm doing the same while writing to a document. But If try to do the same with FeedItem it says "FeedItem.ContentData is not writeable" so I've tried the following code:

FeedItem imageFeedItem = [select Id, ContentData, RelatedRecordId from FeedItem where Id = :imageFeedItemId];

            ContentVersion content = new ContentVersion();
            content.versionData = EncodingUtil.Base64Decode(EncodingUtil.Base64Encode(imageFeedItem.ContentData) + base64BlobValue);
            content.pathOnClient = fileName;

            content.ContentDocumentId = [Select ContentDocumentId from ContentVersion where id=:imageFeedItem.RelatedRecordId].ContentDocumentId;

            insert content;

But this creates ContentVersions of incomplete chunks. Any pointers on how can I achieve this more neat.

Thank you.