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

Việt Hùng Nguyễn hungtrodt5 at gmail.com
Wed Jan 1 12:35:42 EET 2020


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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