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

[tim nicholson]

On 08/06/15 16:24, Michael Niedermayer wrote:
> 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 ?
> is there some specification that limits the VBV buffer size to a
> lower value for "40mbit/sec" than "50mbit/sec" ?
> 

The VBV size for 40M will be lower than for 50M as its limited to 1
frame which is smaller (by about 25/30), its more a question of why the
NTSC bitrate figure is diferent to PAL when there is no other constraint
as to the maximum frame size which we are nowhere near at this bit rate.

The standard "Operating Points" only provide the nominal values.
> [...]


-- 
Tim.
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