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• nal_ref_idc value for the last frame in GOP when B frame is there for x264 encoding

  21 février 2018, par MSD Paul

  nal_ref_idc value during x264 encoding for each frame signifies that whether decoder has to remember or keep those frames in memory or not or in other words, whether those are reference pictures or not.

  In general, I frame with nal_ref_idc value =3 and for P frames, the value = 2.

  If one considers the GOP of this pattern, IPPPIPPP......

  then why the last P also has a nonzero value of 2. I think it should be 0.

  can anyone please tell why the last frame has nonzero nal value?

• Change in NAL_REF_IDC value for P frames in x264 encoding

  19 février 2018, par MSD Paul

  By changing nal_ref_idc value from 2 to 0 for all P frames in x264 encoding, I have observed the size of the P frames gets changed. Is it because of all P frames are now only referenced to a single I frame in GOP?

  But the size of the first P frame after I frame should be independent of both the situation (whether direct encoding, nal_ref_idc = 0 or cumulative encoding, nal_ref_idc = 2), but I am getting a change of size in first P frame also after the I frame. Can anyone please tell me the possible reason or explanation behind this?

• i_nal_ref_idc parameter in x264 encoding

  17 février 2018, par MSD Paul

  can anyone please tell me what i_nal_ref_idc parameter implies in x264 encoding?

  for P frames,i_nal_ref_idc =2 (in general) but if I make it = 0 what does it implies?

• Supporting dependency of P frame on I frame only

  16 février 2018, par MSD Paul

  I have a doubt on x264 encoding.

  If I have IP_1P_2P_3 IPPP some kind of this GOP from the x264 encoded output. Then in general, P_3 will be dependent on I, P_1 and P_2, P_2 will be dependent on I and P_1 (a cumulative encoding).

  Can anyone please give me any ideas how can I support direct encoding so that all P_1, P_2, P_3 will be only dependent on the I frame?

• P frame dependencies and NAL value

  15 février 2018, par MSD Paul

  Can anyone please tell me what is the difference between this two encoded outputs (N.B. the inputs are same, and the parameters I used while encoding are also same)?

  For the first set I am getting the NAL value =2 for P frame. for 2nd set I am getting the NAL value for P frames = 0.

  Can anyone tell me which one is possibly cumulatively encoded and which one is directly encoded means P frames only dependent on I frame not on previous P frames.

  output set1:

  x264 [debug]: frame=   0 QP=28.71 NAL=3 Slice:I Poc:0   I:32768 P:0    SKIP:0    size=335621 bytes
  x264 [debug]: frame=   1 QP=29.62 NAL=2 Slice:P Poc:2   I:1028 P:14500 SKIP:17240 size=60797 bytes
  x264 [debug]: frame=   2 QP=30.29 NAL=2 Slice:P Poc:4   I:962  P:13307 SKIP:18499 size=61788 bytes
  x264 [debug]: frame=   3 QP=30.30 NAL=2 Slice:P Poc:6   I:905  P:13260 SKIP:18603 size=62136 bytes
  x264 [debug]: frame=   4 QP=26.45 NAL=3 Slice:I Poc:0   I:32768 P:0    SKIP:0    size=435864 bytes
  

  output set2:

  x264 [debug]: frame=   0 QP=28.70 NAL=3 Slice:I Poc:0   I:32768 P:0    SKIP:0    size=335363 bytes
  x264 [debug]: frame=   1 QP=33.38 NAL=0 Slice:P Poc:2   I:924  P:11507 SKIP:20337 size=37314 bytes
  x264 [debug]: frame=   2 QP=33.28 NAL=0 Slice:P Poc:4   I:1518 P:13596 SKIP:17654 size=55535 bytes
  x264 [debug]: frame=   3 QP=33.27 NAL=0 Slice:P Poc:6   I:2211 P:14007 SKIP:16550 size=70488 bytes
  x264 [debug]: frame=   4 QP=26.45 NAL=3 Slice:I Poc:0   I:32768 P:0    SKIP:0    size=436369 bytes