Format: Transcript (a printed copy of the speech)
The original date of the speech is not required, but it may be included if the date is certain and considered helpful for your reader. The type of source (in this case, “Transcript”) is also optional, and may be included if the format is unexpected.
Format: Audio Recording and Transcript
In this case, Martin Luther King, Jr. is considered the author since this is primarily his speech. The date of the speech and the name of the host are optional elements. The date the show aired should be included since it is clearly stated in the article. The type of source (“Audio” and “Transcript”) are optional, but may be included if this is considered helpful information for your reader.
Format: Video Recording
Since this is a YouTube URL, it is assumed that the format is a video, and the source type (“Video”) has been omitted.
In this case, “May 2015” refers to when the lecture was posted to the website, not the date of the actual lecture. Therefore, the date comes after the name of the site, pointing back to the element closest to the date.
When speeches are republished in an anthology or book, the original date of the speech is not required, but may be included if it is considered helpful for your reader. The page range is also optional. If the speech is found in an eBook, the name of the database and the URL should be included.
In this case, the date that the speech was given is included in the title, so there is no need to repeat the date.
The terms “Lecture” or “Address” are optional and may be used to indicate that the speech was heard in person.