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negin tebyani
I have two videos that I encoded them with ffmpeg, like:

ffmpeg -i 1_med.mp4 -movflags faststart -c:v libx264 -x264opts
'keyint=100:min-keyint=25:no-scenecut:8x8dct:sliced-threads=0' -deblock 1:1
-flags +loop -b:v 850k -maxrate 850k -bufsize 2000k -nal-hrd cbr -vf
"scale=-1280:720:flags=spline+full_chroma_inp+full_chroma_int+accurate_rnd+bitexact"
-acodec libfdk_aac -b:a 320k -coder 1 -me_range 16 -bf 10 -q:v 1 -qmin 0
-qmax 69 -trellis 2 -mbtree 1 -mixed-refs 1 -preset veryslow medfull.mp4


ffmpeg -i 1_high.mp4 -movflags faststart -c:v libx264 -x264opts
'keyint=100:min-keyint=25:no-scenecut:8x8dct:sliced-threads=0' -deblock 1:1
-flags +loop -b:v 1024k -maxrate 1024k -bufsize 2500k -nal-hrd cbr -vf
"scale=-1280:720:flags=spline+full_chroma_inp+full_chroma_int+accurate_rnd+bitexact"
-acodec libfdk_aac -b:a 320k -coder 1 -me_range 16 -bf 10 -q:v 1 -qmin 0
-qmax 69 -trellis 2 -mbtree 1 -mixed-refs 1 -preset veryslow highfull.mp4

according to mp4box tutorials that I have read about making mpeg-dash, I
know that I have to set keyint and minkey int equal and also related to
segment duration. so I tries using min-keyint=100, but the result video had
the min-keyint=51

so I returned to 25. because the FPS is 25 also.

how can I fix this?? my final dash video has some frame freezes, and i
think it is related to this issue.
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Re: (no subject)

Erik Slagter
> according to mp4box tutorials that I have read about making mpeg-dash, I
> know that I have to set keyint and minkey int equal and also related to
> segment duration. so I tries using min-keyint=100, but the result video had
> the min-keyint=51

Do the tutorials also explain why you would ever want to use a braindead
(!) fixed gop size in the first place?

I could imagine a requirement for a closed gop type, but really not why
you'd want to be gop's always exactly the same length, it's making
encoding really inefficient.

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negin tebyani
mp4box group has said that gop length has to be fixed and the same lengh
for input videos, otherwise the dash video will not play well.


> Do the tutorials also explain why you would ever want to use a braindead
> (!) fixed gop size in the first place?
>
> I could imagine a requirement for a closed gop type, but really not why
> you'd want to be gop's always exactly the same length, it's making encoding
> really inefficient.
>
>
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Re: (no subject)

Erik Slagter
On 17-04-17 13:25, negin tebyani wrote:

 >> Do the tutorials also explain why you would ever want to use a braindead
 >> (!) fixed gop size in the first place?
 >>
 >> I could imagine a requirement for a closed gop type, but really not why
 >> you'd want to be gop's always exactly the same length, it's making
encoding
 >> really inefficient.

> mp4box group has said that gop length has to be fixed and the same lengh
> for input videos, otherwise the dash video will not play well.

That's not really an explanation.

Don't top-post.
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Re: (no subject)

Reuben Martin
In reply to this post by Erik Slagter
On Monday, April 17, 2017 6:22:18 AM CDT Erik Slagter wrote:

> > according to mp4box tutorials that I have read about making mpeg-dash, I
> > know that I have to set keyint and minkey int equal and also related to
> > segment duration. so I tries using min-keyint=100, but the result video
> > had
> > the min-keyint=51
>
> Do the tutorials also explain why you would ever want to use a braindead
> (!) fixed gop size in the first place?
>
> I could imagine a requirement for a closed gop type, but really not why
> you'd want to be gop's always exactly the same length, it's making
> encoding really inefficient.

If you encode a DASH stream with multiple representations (dynamic streaming
with multiple resolutions / bitrates) you have no way to ensure that the
encoders for the different resolutions and / or bitrates set the exact same
GOP boundaries and segmentation on the same frames. Without some way to slave
encoder processes to one master encoder process with respect to GOP, frame-
type decisions and segmentation, locking down the GOP to a set size is the
only way to ensure that.

Would be awesome if ffmpeg / x264 developed a way to provide that master -
slave IPC between different encode sub-processes.

May not apply to this specific situation, but I think that is the thinking
behind the strict GOP size recommendation.

-Reuben


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