[FFmpeg-user] IMX50 NTSC framesize differs to the SMPTE 356M-2001 Standard - why?

[Christoph Gerstbauer]

Am 08.06.15 um 17:24 schrieb Michael Niedermayer:
> On Wed, Jun 03, 2015 at 04:28:48PM +0200, Christoph Gerstbauer wrote:
>>>> yes, this happens because 50mbit/sec is not correct
>>>> a max framesize of 208541 results in a bit rate of max
>>>> 49.999840 mbit/sec, IIUC thats what the spec means by 50mbit/sec
>>> The spec actually says "Up to 50Mb/s" and "Up to 208541" that being the
>>> highest value that comes out below the the 50Mb/s. So I tend to agree
>>> with Michael.
>>>
>> Hi, i have made a short excel calulation and I think that these
>> settings/syntaxes should be the correct ones for PAL/NTSC D-10:
>> Do you agree?
>>
>>
>> 	
>> 	
>> 	
>> 	
>> 	
>> 	
>> 	minrate
>>
>> 	
>> 	framerate 	max coded 	bits/byte 	bufsize 	
>> 	maxrate
>>
>> 	
>> 	
>> 	framesize (Bytes) 	
>> 	rc_init_occupancy 	video bitrate
>> IMX50 	PAL 	25 	250000 	8 	2000000 	
>> 	50000000
>>
>> 	
>> 	
>> 		
>> 	
>> 	
>> 	
>> IMX40 	PAL 	25 	200000 	8 	1600000 	
>> 	40000000
>>
>> 	
>> 	
>> 		
>> 	
>> 	
>> 	
>> IMX30 	PAL 	25 	150000 	8 	1200000 	
>> 	30000000
>>
>> 	
>> 	
>> 		
>> 	
>> 	
>> 	
>>
>> 	
>> 	
>> 		
>> 	
>> 	
>> 	
>>
>> 	
>> 	
>> 		
>> 	
>> 	
>> 	
>> IMX50 	NTSC 	29,97003 	208541 	8 	1668328 	
>> 	49999840,16
>>
>> 	
>> 	
>> 		
>> 	
>> 	
>>
>> IMX40 	NTSC 	29,97003 	166833 	8 	1334664 	
>> 	39999920,08
> i seem to have missed this reply, my question is basicylly the same
> as tims, where does the limit resulting in 39999920 come from ?
Hi, I compared different encoder IMX40 formats, and all of these format 
has a pkt size of 166833bytes (=1 frame for IMX40).
-> 166833*8*(30000/1001) = 39999920bits
> is there some specification that limits the VBV buffer size to a
> lower value for "40mbit/sec" than "50mbit/sec" ?
Maybe I didnt understand the using of the VBV buffer?
I thought the VBV buffer size is always ONE frame. So it differs in size 
when using the 50, 40 or 30 mbit format. Is this wrong?

from SMPTE S356M - 2001 - Type D-10 Stream Specifications:

" The vbv_delay parameter shall be constrained to a *1-frame* delay for 
each GOP by defining the following values:

525/60 systems

– picture_header: vbv_delay = 0BBBh

625/50 systems

– picture_header: vbv_delay = 0E10h"

best regards
Christoph