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nvh264enc: Support intra refresh

Amotz Terem requested to merge amotzte/gst-plugins-bad:infra_refresh into master


NVENCODE API provides a mechanism to implement intra refresh. The enableIntraRefresh flag should be set to 1 in order to enable intra refresh. intraRefreshPeriod determines the period after which intra refresh would happen again and intraRefreshCnt sets the number of frames over which intra refresh would happen.

Intra Refresh causes consecutive sections of the frames to be encoded using intra macroblocks, over intraRefreshCnt consecutive frames. Then the whole cycle repeats after intraRefreshPeriod frames from the first intra-refresh frame. It is essential to set intraRefreshPeriod and intraRefreshCnt appropriately based on the probability of errors that may occur during transmission. For example, intraRefreshPeriod may be small like 30 for a highly error prone network thus enabling recovery every second for a 30 FPS video stream. For networks that have lesser chances of error, the value may be set higher. Lower value of intraRefreshPeriod comes with a slightly lower quality as a larger portion of the overall macroblocks in an intra refresh period are forced to be intra coded, but provides faster recovery from network errors.

intraRefreshCnt determines the number of frames over which the intra refresh will happen within an intra refresh period. A smaller value of intraRefreshCnt will refresh the entire frame quickly (instead of refreshing it slowly in bands) and hence enable a faster error recovery. However, a lower intraRefreshCnt also means sending a larger number of intra macroblocks per frame and hence slightly lower quality.

Edited by Amotz Terem

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