[Mp4-tech] about frame number of H.264 videos

[Wesley De Neve]

Dear Hong Liu,
Simply speaking, frame_num is a syntax element that acts as a counter that is incremented for every reference picture (as such, its value is not incremented for non-reference pictures). The POC acts as a counter that signals the relative order of the pictures, stored in the H.264/AVC bitstream, in output/display order. Both counters are reset to zero by an IDR picture or when their maximum value is reached. 
A search through the archives of this mailing list should also be helpful to you, as the semantics of frame_num and the POC have already been discussed a number of times before. For your purposes (detection of intentional or unintential loss of pictures), it is likely that it is already sufficient to monitor the value of the pic_order_cnt_lsb syntax element in the slice header syntax structure. Also, note that applications might rely on systems level behavior in order to detect picture loss (e.g., by means of functionality provided by the RTP protocol).
Best regards,
Wesley De Neve
  ----- Original Message ----- 
  From: hong liu 
  To: mp4-tech lists.mpegif.org 
  Sent: Tuesday, July 24, 2023 4:43 PM
  Subject: [Mp4-tech] about frame number of H.264 videos
  Now I intend to find out the lost frame number from received h.264 streaming videos. I found there are some parameters in the h264 header information, like frame_num, POC, Picutre_order_present, and so forth. I am a little confused about how to use them to get the lost frame number from corrupted h264 video. Any help is very apprecaited.
  Hong Liu
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