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

[Henk D. Schoneveld]

> 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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