A content item aggregation method, comprising: Obtaining, by a client, a media presentation description of a first media presentation, wherein the first media presentation comprises a content item, the media presentation description comprises a description of the content item or the media presentation description comprises pointing information about a description of the content item, the description of the content item is used to indicate that the content item comes from a second media presentation, and the first media presentation and the second media presentation are different media presentations; and obtaining, by the client, the content item according to the description of the content item; and playing, by the client, the content item; the description of the content item is further used to indicate that a part or an entirety of the content item is embedded in the first media presentation; when the description of the content item is further used to indicate that a part of the content item is embedded in the first media presentation, the description of the content item is further used to indicate a start play time position and/or an end play time position of the part of the content item; characterized in that the description of the content item comprises an offset indication fz, and the offset indication fz is used to indicate an offset between a start play time position and a start content time position of the content item; when the second media presentation is a real-time media presentation, and the offset indicated by the offset indication fz is equal to 0, it indicates that the content item starts to be played from a content position corresponding to a current time; or when the second media presentation is a real-time media presentation, and the offset indicated by the offset indication fz is not equal to 0, it indicates that the content item starts to be played from a content position corresponding to a current time that is set back by the offset; or when the second media presentation is a real-time media presentation, and the offset indicated by the offset indication fz is not equal to 0, it indicates that the content item starts to be played from a content position corresponding to the start content position of the content item that is backward offset by the offset. Obtaining, by a client, a media presentation description of a first media presentation, wherein the first media presentation comprises a content item, the media presentation description comprises a description of the content item or the media presentation description comprises pointing information about a description of the content item, the description of the content item is used to indicate that the content item comes from a second media presentation, and the first media presentation and the second media presentation are different media presentations; and obtaining, by the client, the content item according to the description of the content item; and playing, by the client, the content item; the description of the content item is further used to indicate that a part or an entirety of the content item is embedded in the first media presentation; when the description of the content item is further used to indicate that a part of the content item is embedded in the first media presentation, the description of the content item is further used to indicate a start play time position and/or an end play time position of the part of the content item; characterized in that the description of the content item comprises an offset indication fz, and the offset indication fz is used to indicate an offset between a start play time position and a start content time position of the content item; when the second media presentation is a real-time media presentation, and the offset indicated by the offset indication fz is equal to 0, it indicates that the content item starts to be played from a content position corresponding to a current time; or when the second media presentation is a real-time media presentation, and the offset indicated by the offset indication fz is not equal to 0, it indicates that the content item starts to be played from a content position corresponding to a current time that is set back by the offset; or when the second media presentation is a real-time media presentation, and the offset indicated by the offset indication fz is not equal to 0, it indicates that the content item starts to be played from a content position corresponding to the start content position of the content item that is backward offset by the offset.