[Mp4-tech] B-frame detection?

[Vasudeva, Harish]

oh, sorry that i forgot to mention that i needed this at the VOL level. I found that i could use the low_delay param to detect the presence of B-Frames. But, next I needed to find the consecutive numbers of B-Frames.
 From the usermanual.doc (in the reference decoder) I found that the number of Bs within Ps should be only 2. Further, I checked out some other streams that DO NOT have P-Frames (just Is & Bs). In these the number of B-Frames between I-Frames was 9 (in all streams). So, I concluded that :
1. If PVOPs are present, then the number of consecutive BVOPS will be 2.
2. If PVOPs are absent (with only IVOPs), then the number of consecutive BVOPS will be 9.
Is that a correct assumption? 
thanx
HV
-----Original Message-----
From: Wesley De Neve [mailto:Wesley.DeNeve ugent.be]
Sent: Tuesday, October 05, 2023 1:51 PM
To: Vasudeva, Harish; Mp4-tech lists.mpegif.org
Subject: Re: [Mp4-tech] B-frame detection?
Hi,
harish.vasudeva amd.com wrote:
> Hi,
>
>  Is there any way of detecting (in the decoder) if B-frames are
> present in the sequence? May be by a combination of bits?

The decoder should check for the value of the vop_coding_type syntax element
in case you're talking about an MPEG-4 Visual Elementary Stream:
      vop_coding_type     coding method
      00                            intra-coded (I)
      01                            predictive-coded (P)
      10                            bidirectionally-predictive-coded (B)
      11                            sprite (S)
Best regards,
-Wesley