Another reason for testing with periodic intra is the recent rise in RTP mixers which switch rather than transcode media. Setting the intra interval to the average active speaker switching time gives a good estimate of real-world codec efficiency in these topologies.
Mo On Mar 15, 2015, at 6:36 AM, Harald Alvestrand <[email protected]> wrote: Forking the subject.... Den 03. mars 2015 10:10, skrev Mohammed Raad: > At MPEG we use this to determine the codec performance for the "random > access" case. I don't know why the 1 second interval was chosen and > don't think that its relevant in many use cases, but MPEG codecs are > aimed at satisfying a broad range of applications and so this test case > has been maintained. Members of the potential IETF activity may find > that this is an irrelevant test case. The reasons for having non-initial I-frames that I know of: - To allow seeking in stored media. To jump to a specific point, you locate the last I-frame before the point you want to go to and run the decoder from that point to the point where you really want to go. With DASH being a prevalent mode of delivering stored media, and each DASH chunk starting with an I-frame, 5 seconds would be realistic for this. - To allow recovery from a known good state in streaming media. For interactive two-way media, you can explicitly ask for an I-frame and have the headend produce it; for other media, such as broadcast (the original use case for half-second intervals, as mentioned above), more complex schemes are needed (I've heard of technologies for storing a reference frame in some other form and transferring it out of band so that the decoder can initialize its state and start decoding without an I-frame, but I don't know if these are used in practice.) _______________________________________________ video-codec mailing list [email protected] https://www.ietf.org/mailman/listinfo/video-codec _______________________________________________ video-codec mailing list [email protected] https://www.ietf.org/mailman/listinfo/video-codec
