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
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