[Libav-user] FFMPEG avformat_write_header changing my stream time_base

[Rafael Lúcio]

You need to manipulate the pts of the packet after encoding and before
writing to the file... Its not unusual to have the time_base of the stream
changed by ffmpeg. Check line 869 of the ffmpeg.c source code at
https://www.ffmpeg.org/doxygen/trunk/ffmpeg_8c-source.html

2015-04-24 13:33 GMT-03:00 cesar pachon <cesarpachon at gmail.com>:

> I am muxing video using ffmpeg 2.1.3 with libavcodec 55.39.101 (forced to
> that version because is the one available in google-chrome PNACL port
> project). all my frames seems to have bad the time. they try to be rendered
> all at once at the beggining of the video when playing it.
>
> I am setting the stream time base to 1/25, but just after calling
> avformat_write_header, it has the value of -18082736/1. in each frame, when
> I print the stream time_base it says 1/12800, while the time_base of codec
> is always ok (1/25).
>
> console log before and after av_format_write_header:
>
> before avformat_write_header stream time_base: 1/25
> after avformat_write_header ret 0 stream time_base: -18082736/1
>
> the code (abreviated to keep the post short, all calls in the original
> version had error checking):
>
> AVCodecContext *codecContext;
> AVCodec * codec = avcodec_find_encoder(codec_id);
> myOutputStream->stream = avformat_new_stream(outputFormatContext, *codec);
> myOutputStream->stream->id = outputFormatContext->nb_streams-1;
> codecContext = myOutputStream->stream->codec;
> codecContext->codec_id = codec_id;
> codecContext->bit_rate = 400000;
> codecContext->width    = width;
> codecContext->height   = height;
> myOutputStream->stream->time_base = (AVRational){ 1, 25 };
> codecContext->time_base       = myOutputStream->stream->time_base;
> codecContext->gop_size      = 12;
> codecContext->pix_fmt       = AV_PIX_FMT_YUV420P;
> AVDictionary *opt = NULL;
> av_dict_copy(&opt, opt_arg, 0);
> ret = avcodec_open2(codecContext, codec, &opt);
> av_dict_free(&opt);
> myOutputStream->frame = alloc_picture(codecContext->pix_fmt,
> codecContext->width, codecContext->height);
>   myOutputStream->tmp_frame = alloc_picture(AV_PIX_FMT_YUV420P,
> codecContext->width, codecContext->height);
>
> //before: printing g_outputContext->stream time_base here
> ret = avformat_write_header(g_outputContext, &opt);
> //after: printing g_outputContext->stream time_base here
>
>
> (note: I also posted this question in stackoverflow:
> http://stackoverflow.com/questions/29850246/ffmpeg-avformat-write-header-changing-my-stream-time-base
> )
>
>
> Cesar  Pachón
> -------------------------------------------------------------
> www.cesarpachon.com, just a digital hermit
>
>
> _______________________________________________
> Libav-user mailing list
> Libav-user at ffmpeg.org
> http://ffmpeg.org/mailman/listinfo/libav-user
>
>


-- 
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Rafael Lúcio
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