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

[Việt Hùng Nguyễn]

I don’t remember exactly but you can use av_copy_context api to copy all
needed parameters

On Wed, Jan 1, 2020 at 17:44 Audric Ackermann <audric.ackermann at gmail.com>
wrote:

> And so, how can I copy all the input parameters? To get the same
> parameters in the recorded file?
>
> Le mer. 1 janv. 2020 à 21:36, Việt Hùng Nguyễn <hungtrodt5 at gmail.com> a
> écrit :
>
>> Yes, exactly!
>>
>> On Wed, Jan 1, 2020, 17:10 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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>>
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>
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