may realize that the audio has already been played or has still not been played presentation time stamps are embedded within encoded content called a packetized elementary stream a presentation time stamp is placed in a packet header to indicate the exact time that a portion of a portion of decoded audio or video data is to be presented to a viewer the encoded content may be any type of audio and video material including movies games or other graphics a renderer is any component that decides when either audio or video is sent to an output device an output device may be a television a monitor an audio video receiver or a computer display to mention some examples generally content contains initial audio and video presentation time stamps close to one another in time the first video frame is displayed very soon after startup and may be close to the first rendered audio sample thereby maintaining audio visual synchronization the actual times may depend on the content and the software and hardware used however in some cases the content may not follow this sequence the content can be encoded so that the first video presentation time stamp comes some amount of time after the first audio presentation time stamp for example in such a case the user hears audio a few seconds before the first video frame in internet protocol streaming this may cause a channel.