GDR Intra Refresh - GDR Intra Refresh - 3.0 English - PG447

Gradual Decoder Refresh (GDR) applies when GOPCtrlMode is set to LOW_DELAY_P or LOW_DELAY_B. The GDRMode parameter specifies whether and which GDR scheme should be used. When GDR is enabled (horizontal or vertical), the encoder inserts an intra MBs row/column in the picture to refresh the decoder. Gop.FreqIDR specifies the frequency at which the refresh pattern should happen. To allow full picture refreshing, Gop.FreqIDR should be greater than the number of CTB/MB rows (GDR_HORIZONTAL) or columns (GDR_VERTICAL).

When GDR is enabled, the encoder inserts an SPS/PPS along with an SEI recovery message at the start of a refresh pattern, thus allowing a decoder to synchronize to the SEI recovery points in the bitstream. The advantage of having non-IDR decoder synchronization is that there is no longer any need to send IDR pictures in case of a packet loss scenario. Inserting periodic IDR pictures in video encoding generates a spike in bit consumption which is not recommended for video streaming.

Vertical GDR mode has a motion vector limitation that can cause full picture reconstruction to take more than one refresh cycle. Refer to the following table for more details:

Use gdr-mode=horizontal and periodicity-idr=<higher than Picture Height in Mbs> in the encoder element.

gst-launch-1.0 filesrc location=in.yuv ! rawvideoparse width=3840 height=2160 format=nv12 framerate=30/1! omxh264enc control-rate=constant target-bitrate=60000 gop-mode=low-delay-p gdr-mode=horizontal periodicity-idr=270! video/x-h264, profile=high! filesink location=out.avc

In an encoder configuration file, add the following section and parameters.

[GOP]
GopCtrlMode = LOW_DELAY_P
Gop.GdrMode = GDR_HORIZONTAL
Gop.FreqIDR = 270