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Random access/Low delay/All intra

All Intra/Random access/Low delay - in terms of video encoding, these terms define the GOP structure of encoded streams. Actually, they define the presence and frequency of key frames (I-frames) in the elementary video stream.

“All intra” mode assumes that all frames in the elementary stream are key frames. The possibility to decode this stream starting from any frame is a benefit of this mode. Low encoding efficiency on the same bitrates is a big lack. Usually, this mode is used for temporal storing and editing video streams before final transcoding.

“Random access” mode assumes that elementary streams contain some key frames which can be used for starting the decoding process. In common these streams contain B-frames also. This mode is used for most cases of final encoding.

“Low delay” mode assumes minimal latency between capturing an image and its display after encoding-broadcasting-decoding pipeline. It may be achieved by avoiding Intra and Bidirectional frames in GOP structure. Also, low delay encoding usually assumes only one reference.