[Libav-user] Change the default audio and video codec loaded by avformat_alloc_output_context2

[Mythili Vishalini Anbazhagan]

Hello,
Thank you so much again for the quick response.
I'll check them.
Thank you.

Best Regards,
Mythili


On Wed, Jun 9, 2021 at 11:06 PM Guangyu Sun via Libav-user <
libav-user at ffmpeg.org> wrote:

> Hi Mythili,
>
> Check these two functions. Setting flvflags to the options should work.
>
> int avformat_write_header(AVFormatContext *s, AVDictionary **options);
> int avformat_init_output(AVFormatContext *s, AVDictionary **options);
>
> Thanks,
> Guangyu
>
> On Tue, Jun 8, 2021 at 9:46 PM Mythili Vishalini Anbazhagan <
> manbazhagan27 at gmail.com> wrote:
>
>> Hello,
>> Thank you so much for the information. I will try that and see.
>>
>> I have found a workaround. Don't know if this is the correct way of doing
>> this though.
>> Created AVOutputFormat using  "AVOutputFormat* oformat = av_guess_format(
>> "flv", NULL, NULL)" and then manually edited the audio and video codec
>> fields in "oformat" before giving it to avformat_alloc_output_context2.
>> It works and I'm able to stream audio and video.
>>
>> But I get the following warning:
>> "Failed to update header with correct duration.Failed to update header
>> with correct filesize."
>> In the command line, I rectified this error with the flag -flvflags
>> no_duration_filesize.
>> Could you tell me how to set this flag in the API ?
>>
>> Thank you so much.
>>
>> Best Regards,
>> Mythili Vishalini.
>>
>>
>> On Tue, Jun 8, 2021 at 11:19 PM Guangyu Sun via Libav-user <
>> libav-user at ffmpeg.org> wrote:
>>
>>> This might be what you are looking for:
>>> AVStream *avformat_new_stream(AVFormatContext *s, const AVCodec *c);
>>>
>>> Specify the correct codec when adding streams to the AVFormatContext
>>> created by avformat_alloc_output_context2().
>>>
>>> On Mon, Jun 7, 2021 at 11:39 PM Mythili Vishalini Anbazhagan <
>>> manbazhagan27 at gmail.com> wrote:
>>>
>>>> Hi,
>>>> I'm using ffmpeg libav library for live streaming via RTMP. I want to
>>>> know how to give my choice of audio and video codec for the particular
>>>> format in avformat_alloc_output_context2.
>>>>
>>>> In Detail:
>>>> The following command works perfectly for me.
>>>> ffmpeg -re -stream_loop -1 -i ~/Downloads/Microsoft_Surface.mp4 -vcodec
>>>> copy -c:a aac -b:a 160k -ar 44100 -strict -2 -f flv -flvflags
>>>> no_duration_filesize rtmp://192.168.1.7/live/surface
>>>> In the output, I have set my audio codec to be aac and copied the video
>>>> codec from input, which is H264.
>>>> I want to emulate this in the library, but don't know how to.
>>>> avformat_alloc_output_context2, with parameter format name as "flv",
>>>> sets oformat audio codec to ADPCM_SWF and video codec to FLV1. How to
>>>> change that to AAC and H264 ?
>>>>
>>>> So far, used av_guess_format to construct AVOutputFormat. It accepts
>>>> only format as input. And I don't know where to mention audio and video
>>>> codec.
>>>> Also tried giving filename to avformat_alloc_output_context2 with the
>>>> rest of the parameters NULL. The file has AAC audio and H264 video. But
>>>> still ffmpeg loads oformat with ADPCM_SWF audio and FLV1 video codecs.
>>>>
>>>> Any hint/guidance is hugely appreciated. Thank you.
>>>>
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>>>>
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