Keyframe

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Keyframe

Mark Filipak
Hey,

I have a question for you knowledgeable folks.

I've seen where some use the term "keyframe" but I've never seen a definition. It's not terribly
important, but here goes...

I've assumed -- you know how good I am at that! -- that a keyframe is the I-frame that's at the
beginning of a GOP.

Am I correct?

Thanks,
Mark.
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Re: Keyframe

Michael Koch
Am 21.04.2020 um 04:09 schrieb Mark Filipak:

> Hey,
>
> I have a question for you knowledgeable folks.
>
> I've seen where some use the term "keyframe" but I've never seen a
> definition. It's not terribly important, but here goes...
>
> I've assumed -- you know how good I am at that! -- that a keyframe is
> the I-frame that's at the beginning of a GOP.
>
> Am I correct?

I think this is correct, see also here:
https://en.wikipedia.org/wiki/Key_frame

Michael

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Glossary? [was: Re: Keyframe]

Jim DeLaHunt-2
On 2020-04-20 22:55, Michael Koch wrote:

> Am 21.04.2020 um 04:09 schrieb Mark Filipak:
>> I've seen where some use the term "keyframe" but I've never seen a
>> definition.…
>
> I think this is correct, see also here:
> https://en.wikipedia.org/wiki/Key_frame

One kind of documentation that I haven't seen around ffmpeg which I
think might be very helpful is a glossary. The ffmpeg documentation uses
many technical terms without defining them, or even pointing to an
conceptual overview that helps a new user understands the abstractions
and terminology used in ffmpeg code and docs.

My first nominations for a glossary: "PTS", "timebase", "muxer",
"demuxer". Also "frame" and "field", per recent threads here. And "GOP",
"I-frames", and "B-frames".

--
     --Jim DeLaHunt, [hidden email]     http://blog.jdlh.com/ (http://jdlh.com/)
       multilingual websites consultant

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Re: Keyframe

Mark Filipak
In reply to this post by Michael Koch
Hey, Michael,

On 04/21/2020 01:55 AM, Michael Koch wrote:

> Am 21.04.2020 um 04:09 schrieb Mark Filipak:
>> Hey,
>>
>> I have a question for you knowledgeable folks.
>>
>> I've seen where some use the term "keyframe" but I've never seen a definition. It's not terribly
>> important, but here goes...
>>
>> I've assumed -- you know how good I am at that! -- that a keyframe is the I-frame that's at the
>> beginning of a GOP.
>>
>> Am I correct?
>
> I think this is correct, see also here:
> https://en.wikipedia.org/wiki/Key_frame
>
> Michael

That Wikipedia article implies pretty strongly that all I-frames are keyframes.

The MPEG spec uses the term "keyframe" occasionally, and in a manner that implies that keyframes are
particular I-frames, but then doesn't really resolve the question regarding what quality makes an
I-frame a keyframe. The only thing I could think of was the particular I-frame that begins a GOP.
There's a problem with that: Not all stream formats have GOPs even though the literature about those
formats refer to keyframes. Maybe in those formats, all I-frames are keyframes. ?????

I guess it's like "interlaced", just another video term that has a 'variable' definition. ;-)

Hopefully, someone else will contribute. For now, there's 2 votes for keyframe == 1st frame of GOP.
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Re: Glossary? [was: Re: Keyframe]

Mark Filipak
In reply to this post by Jim DeLaHunt-2
On 04/21/2020 02:12 AM, Jim DeLaHunt wrote:

> On 2020-04-20 22:55, Michael Koch wrote:
>
>> Am 21.04.2020 um 04:09 schrieb Mark Filipak:
>>> I've seen where some use the term "keyframe" but I've never seen a definition.…
>>
>> I think this is correct, see also here:
>> https://en.wikipedia.org/wiki/Key_frame
>
> One kind of documentation that I haven't seen around ffmpeg which I think might be very helpful is a
> glossary.

doG bless you, Jim.

> The ffmpeg documentation uses many technical terms without defining them, or even pointing
> to an conceptual overview that helps a new user understands the abstractions and terminology used in
> ffmpeg code and docs.
>
> My first nominations for a glossary: "PTS", "timebase", "muxer", "demuxer". Also "frame" and
> "field", per recent threads here. And "GOP", "I-frames", and "B-frames".

I've written a glossary. Should I post it? ...Warning: It's bound to be controversial.


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Re: Glossary? [was: Re: Keyframe]

Paul B Mahol
On 4/21/20, Mark Filipak <[hidden email]> wrote:

> On 04/21/2020 02:12 AM, Jim DeLaHunt wrote:
>> On 2020-04-20 22:55, Michael Koch wrote:
>>
>>> Am 21.04.2020 um 04:09 schrieb Mark Filipak:
>>>> I've seen where some use the term "keyframe" but I've never seen a
>>>> definition.…
>>>
>>> I think this is correct, see also here:
>>> https://en.wikipedia.org/wiki/Key_frame
>>
>> One kind of documentation that I haven't seen around ffmpeg which I think
>> might be very helpful is a
>> glossary.
>
> doG bless you, Jim.

Not again.


>
>> The ffmpeg documentation uses many technical terms without defining them,
>> or even pointing
>> to an conceptual overview that helps a new user understands the
>> abstractions and terminology used in
>> ffmpeg code and docs.
>>
>> My first nominations for a glossary: "PTS", "timebase", "muxer",
>> "demuxer". Also "frame" and
>> "field", per recent threads here. And "GOP", "I-frames", and "B-frames".
>
> I've written a glossary. Should I post it? ...Warning: It's bound to be
> controversial.
>

Not again.
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Re: Glossary? [was: Re: Keyframe]

Mark Filipak
On 04/21/2020 04:40 AM, Paul B Mahol wrote:
> On 4/21/20, Mark Filipak <[hidden email]> wrote:
>> doG bless you, Jim.
>
> Not again.

Well, may doG bless you also, Paul.

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Re: Glossary? [was: Re: Keyframe]

Rob Hallam-2
In reply to this post by Mark Filipak
>
> On 04/21/2020 02:12 AM, Jim DeLaHunt wrote:
>
> > One kind of documentation that I haven't seen around ffmpeg which I
> think might be very helpful is a
> > glossary.
>

Agreed. While many won't read it before posting it is at least something
that could be pointed to in replies, FAQs, docs etc. Given the amount of
time spent trying to get people to use terminology consistently, it should
be a net win; or at least save some typing.

Lots of information is available but spread out. Some terms are defined on
old, closed StackOverflow questions (with reference back to this ML), eg:

https://stackoverflow.com/a/3199582/4647265
http://ffmpeg-users.933282.n4.nabble.com/What-does-the-output-of-ffmpeg-mean-tbr-tbn-tbc-etc-td941538.html

It's not a problem when it can be found, but it would be useful for folks
learning to have it consolidated in one place.

On Tue, 21 Apr 2020 at 07:30, Mark Filipak <
[hidden email]> wrote:

>
> I've written a glossary. Should I post it? ...Warning: It's bound to be
controversial.

Yes. The cliché is 'patches welcome', though obviously I don't speak for
the project. If nothing else, I would be interested in reading/referring to
a glossary.

Cheers,
Rob
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