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

[Christoph Gerstbauer]

>>> 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
> Approximately!
>
>>> 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?
> I think this is correct, I think Michael's question was slighly confusing.
>
>> 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"
>>
> But why does having a 1 frame delay, and therefore one frame buffer
> which requires different buffer sizes for PAL and NTSC due to the frame
> rate difference, require the bit rates to be different? The only reason
> this is the case for the nominal 50M Operating point is because having
> exactly 50M at 30000/1001 would lead to frames larger than the maximum
> coded frame size. At lower bit rates this is not an issue.
>
> so buffer size = 40000000 x 1001/30000 = 1334667 (approx)
>
> Given the frame rates getting integer values all round is impossible and
> even your figures contain rounding errors. So there will always be some
> fudging somewhere. Quite how the coder copes with these slightly
> incomatible constraints I am unclear.
>
Hello Tim,

I am now very confused about this issue, I didnt get your point.
1.) Please can you tell me YOUR used syntaxes for IMX30/40/50  for PAL 
and NTSC? I want to compare it to mine.
I just want to find THE syntax for IMX50/40/30 D-10 MXFs for the ffmpeg 
encoding, so that it matches with the SMPTE D-10 standard paper.

2.) Furthermore: For IMX30 and 40 -> Do you think I can always use 
framebuffer size from the IMX50 format and no decoder will have a 
problem with that?

best regards
christoph