[FFmpeg-user] Use force_key_frames to obtain keyframes at exactly the same positions as in the input stream?

[Anatol]

It does not matter the type of the incoming protocol.
And slight un-alignment tolerated by the CDN providers and Apple HLS
validation tools.
Therefore the source live stream can be used in an adaptive-bitrate sets,
IF the other streams match their key frames.
By the way Wowza has this option ("keep Source key frames") in its
Transcoder add-on.
But Wowza also has other problems ...


On Sat, May 2, 2015 at 11:06 AM, Henk D. Schoneveld <belcampo at zonnet.nl>
wrote:

>
> > On 02 May 2015, at 06:27, Anatol <anatol2002 at gmail.com> wrote:
> >
> > The idea is to gain the option to use the H264 source stream along with
> > live transcoded streams in an adaptive bitrate delivery modes (HLS, HDS,
> > etc), that require aligned keyframes on ALL participating streams.
> Could it be ALL, except the livestream itself ?
> Or is the livestream also available via HLS ?
> If yes, then you’ll have to encode this one as well.
> This can only be achieved if the source stream is encoded with the same
> version of the encoder you’re using your self. I can imagine that different
> encoders could behave slightly different.
> BTW what is your source ? Is it predictable like DVB-S from the same
> broadcaster ?
> From the top of my head BBC broadcast has an I-frame every 12 or 13 frames.
> Another potential issue could be the delay between the video and audio
> stream, which would force you to also encode the source stream.
> Hope it helps.
> >
> > On Sat, May 2, 2015 at 2:48 AM, Henk D. Schoneveld <belcampo at zonnet.nl>
> > wrote:
> >
> >>
> >>> On 01 May 2015, at 20:43, Haris Zukanovic <haris.zukanovic74 at gmail.com
> >
> >> wrote:
> >>>
> >>> Indeed force-ing keyframes at certain positions is meant to keep
> multiple
> >>> output encodings keyframe aligned. The input stream is already h264 in
> >> our
> >>> case.
> >>> Moreover, if one could "copy" all iframe positions, and possibly also
> all
> >>> other frametypes from the input stream there would not be any need for
> >>> scene detection if that was already done in the input stream. I am not
> >> sure
> >>> how much heavy lookahead calculations and perhaps other heavy
> >> calculations
> >>> could also be skipped?
> >> What are you trying to achieve ? A performance boost ? I don’t think
> that
> >> you’ll achieve improvement worthwhile, if anything at all. The working
> of
> >> the encoder should need to be totally rewritten to make something like
> this
> >> happen at all. Encoding of a frame depends on former and following
> frames,
> >> the result I P or B frame is the result. Your source is h264  already,
> so I
> >> think you’ll rescale and re-encode to achieve that. The calculation has
> to
> >> be done. Knowing in advance that it will be en I P or B frame won’t make
> >> any difference in the amount of calculations in my opinion.
> >>> On May 1, 2015 7:42 PM, "Henk D. Schoneveld" <belcampo at zonnet.nl>
> wrote:
> >>>
> >>>>
> >>>>> On 01 May 2015, at 13:06, Haris Zukanovic <
> haris.zukanovic74 at gmail.com
> >>>
> >>>> wrote:
> >>>>>
> >>>>> Is the decision about exactly which frame to make an IDR frame made
> in
> >>>> x264 or ffmpeg?
> >>>> In general I-frames are placed at scene-changes, this can happen
> random.
> >>>> Additionally you can can force an I-frame every arbitrary amount of
> >> frames
> >>>> by specifying the gop-size. The function of an I-frame is to hold max
> >> frame
> >>>> info P and B frames build on that complete I-frame. It doesn’t make
> >> sense
> >>>> from an encoding viewpoint to skip an I-frame at a scene-change, it’s
> >> just
> >>>> impossible.
> >>>> Adding more than ‘a minimum amount’ of I-frames only makes sense for
> >>>> seeking purposes, at the cost of less compression/higher then
> necessary
> >>>> bitrate.
> >>>>> Any pointer or advice on where to look for this in the code?
> >>>>>
> >>>>>
> >>>>> On 4/29/15 8:54 PM, Anatol wrote:
> >>>>>> No responses on that one?
> >>>>>> It is very important issue.
> >>>>>>
> >>>>>> On Mon, Apr 27, 2015 at 11:47 PM, Haris Zukanovic <
> >>>>>> haris.zukanovic74 at gmail.com> wrote:
> >>>>>>
> >>>>>>> Hello,
> >>>>>>> Can I use force_key_frames in some way to produce keyframes (IDR,
> not
> >>>>>>> I-frames) at exactly the same PTS in output streams as they are
> found
> >>>> in
> >>>>>>> the live input stream? Both input and output are h264 and live
> >>>> streaming.
> >>>>>>>
> >>>>>>> Something analogous to using 2 pass encoding for VOD and in the
> >> second
> >>>>>>> pass keyframes are inserted exactly where they are recorded in the
> >>>> first
> >>>>>>> pass... Is that something like that even theoretically doable for
> >> live
> >>>>>>> streaming?
> >>>>>>>
> >>>>>>>
> >>>>>>>
> >>>>>>> thanx
> >>>>>>>
> >>>>>>> --
> >>>>>>> --
> >>>>>>> Haris Zukanovic
> >>>>>>>
> >>>>>>> _______________________________________________
> >>>>>>> ffmpeg-user mailing list
> >>>>>>> ffmpeg-user at ffmpeg.org
> >>>>>>> http://ffmpeg.org/mailman/listinfo/ffmpeg-user
> >>>>>>>
> >>>>>> _______________________________________________
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> >>>>>
> >>>>> --
> >>>>> --
> >>>>> Haris Zukanovic
> >>>>>
> >>>>> _______________________________________________
> >>>>> ffmpeg-user mailing list
> >>>>> ffmpeg-user at ffmpeg.org
> >>>>> http://ffmpeg.org/mailman/listinfo/ffmpeg-user
> >>>>
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> >>>>
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> >>
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