[x264-devel] HRD buffer overflow

[Jason Garrett-Glaser]

On Fri, May 25, 2012 at 9:19 AM, Steve Li <steve.li at digitalrapids.com> wrote:
> Hi all,
>
>
>
> I am getting HRD buffer overflow warnings from the Tektronix analyzer when I
> analyze the output of the x264 encoder. Below are the x264 parameters:
>
>
>
> profile=High
>
> level=4
>
> i_nal_hrd=2 (CBR)
>
> rc.i_bitrate=3500
>
> rc.vbv_buffer_size=3500
>
>
>
> Input is 1920x1080p29.97
>
>
>
> The warning happens quite often in the output (over 20 warnings within 10
> secs). Here is one of the warnings from the Tektronix analyzer:
>
> Hypothetical Reference Decoder SchedSelIdx = 0 model has overflowed by 7
> bits at time 1.000s.The overflow occurred during the decoding of frame 21,
> bitstream position 0x65e57 (dec. 417367).  The total HRD buffer occupancy is
> 3500007 bits and the maximum limit is 3500000 bits.

This sounds like a rounding error in the analyzer; given that H.264 is
stored in a bytestream format, it seems rather impossible for it to
overflow by 7 bits.  We've encountered HRD rounding errors in
analyzers before, so this wouldn't be a new thing.

Kieran might be able to shed some more light?

Jason