[Libav-user] Preview video and start recording with exact same stream settings

[Audric Ackermann]

OK thanks, that's a good idea.
I don't know much but I can basically write the last keyframe to the file
and then write the last packets received after pressing record? I mean,
between two key frames, all frames are dependent on the key frame only?

How can I check if the keyframe I got is a keyframe?

Audric

Le mer. 1 janv. 2020 à 22:43, Strahinja Radman <dr.strashni at gmail.com> a
écrit :

> Well, you can do this. Keep last N number of packets in a buffer, where N
> is guaranteed to contain keyframe packet. When you encounter new keyframe
> packet
> you can free the packets that are not needed anymore. When someone starts
> to record, you can mux from the last known key frame packet.
>
> On Wed, Jan 1, 2020 at 11:10 AM Audric Ackermann <
> audric.ackermann at gmail.com> wrote:
>
>> But if I want to avoid missing the first few frames  which are not a key
>> frame, I have to reencode the data, so the first frame recorded is a key
>> frame, right?
>>
>> Le mer. 1 janv. 2020 à 20:49, Strahinja Radman <dr.strashni at gmail.com> a
>> écrit :
>>
>>> If you only want to copy the input, there is no need to transcode. You
>>> can simply duplicate the input packets, one packet goes to the decoder so
>>> it can be shown, the other
>>> goes to the muxer for the recorder when someone presses the record
>>> button. You can save to whatever format you want but input may not be
>>> playable from the start until
>>> it reaches the key frame. Deep packet copy can be achieved with the
>>> following code:
>>>
>>> AVPacket packet;
>>> av_init_packet(&packet);
>>> av_packet_ref(packet, src);
>>> av_packet_make_writable(&packet);
>>>
>>> You can based on the decoded frames, mark a key frame packet and start
>>> saving from there.
>>>
>>> On Wed, Jan 1, 2020 at 10:06 AM Audric Ackermann <
>>> audric.ackermann at gmail.com> wrote:
>>>
>>>> Ok thank you.
>>>> As I do not control the input parameters I will go for the transcode
>>>> option. Is there an easy way to duplicate all required decoder parameters
>>>> to the encoder?
>>>>
>>>> Like doing this, but with all important params in one step:
>>>>
>>>> Thanks
>>>>
>>>> outst->codec->width = this->codec_ctx->width;
>>>> outst->codec->height = this->codec_ctx->height;
>>>> outst->codec->pix_fmt = this->codec_ctx->pix_fmt;
>>>> outst->codec->time_base = this->codec_ctx->time_base;
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>>>
>>>
>>>
>>> --
>>>
>>> Regards
>>> Strahinja Radman
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>>>
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>>> libav-user-request at ffmpeg.org with subject "unsubscribe".
>>
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>
>
>
> --
>
> Regards
> Strahinja Radman
> _______________________________________________
> Libav-user mailing list
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>
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