I am trying to develop a webrtc simulator in C/C++. For media handling, I
plan to use *libav*. I am thinking of below steps to realize media exchange
between two webrtc simulator. Say I have two webrtc simulators *A* and *B*.
1. Read media at A from a input webm file using *av_read_frame* api.
2. I assume I will get the encoded media (audio / video) data, *am I
correct here?*
3. Send the encoded media data to simulator *B* over a UDP socket.
4. Simulator *B* receives the media data in UDP socket as RTP packets.
5. Simulator *B* extracts audio/video data from just received RTP packet.
6. I assume the extracted media data at simulator *B* are the encoded
data only (*am I correct here*). I do not want to decode it. I want to
write it to a file. Later I will play the file to check if I have done
everything right.
To simplify this problem lets take out UDP socket part. Then my question
reduces to read data from a webm input file, get the encoded media, prepare
the packet and write to a output file using *av_interleaved_write_frame* or
any other appropriate api. All these things I want to do using libav.
Is there any example code I can refer.
Or can somebody please guide me to develop it.
I am trying with a test program (given below). As a first step, my aim is
to read from a file and write to an output file. I have below code, but it
is not working properly.
*//#define _AUDIO_WRITE_ENABLED_*
> *#define _VIDEO_WRITE_ENABLED_*
>
> *#include "libavutil/imgutils.h"*
> *#include "libavutil/samplefmt.h"*
> *#include "libavformat/avformat.h"*
>
> *static AVPacket pkt;*
> *static AVFormatContext *fmt_ctx = NULL;*
> *static AVFormatContext *av_format_context = NULL;*
> *static AVOutputFormat *av_output_format = NULL;*
>
> *static AVCodec *video_codec = NULL;*
> *static AVStream *video_stream = NULL;*
>
> *static AVCodec *audio_codec = NULL;*
> *static AVStream *audio_stream = NULL;*
>
>
> *static const char *src_filename = NULL;*
> *static const char *dst_filename = NULL;*
>
> *int main (int argc, char **argv)*
> *{*
> * int ret = 0;*
> * int index = 0;*
>
> * if (argc != 3) *
> * {*
> * printf("Usage: ./webm input_video_file output_video_file \n");*
> * exit(0);*
> * }*
>
> * src_filename = argv[1];*
> * dst_filename = argv[2];*
>
> * printf("Source file = %s , Destination file = %s\n", src_filename,
> dst_filename);*
>
> * av_register_all();*
>
> * /* open input file, and allocate format context */*
> * if (avformat_open_input(&fmt_ctx, src_filename, NULL, NULL) < 0) *
> * {*
> * fprintf(stderr, "Could not open source file %s\n", src_filename);*
> * exit(1);*
> * }*
>
> * /* retrieve stream information */*
> * if (avformat_find_stream_info(fmt_ctx, NULL) < 0) *
> * {*
> * fprintf(stderr, "Could not find stream information\n");*
> * exit(2);*
> * }*
>
> * av_output_format = av_guess_format(NULL, dst_filename, NULL);*
> * if(!av_output_format)*
> * {*
> * fprintf(stderr, "Could not guess output file format\n");*
> * exit(3);*
> * }*
>
> * av_output_format->audio_codec = AV_CODEC_ID_VORBIS;*
> * av_output_format->video_codec = AV_CODEC_ID_VP8;*
>
> * av_format_context = avformat_alloc_context();*
> * if(!av_format_context) *
> * {*
> * fprintf(stderr, "Could not allocation av format context\n");*
> * exit(4);*
> * } *
> * av_format_context->oformat = av_output_format;*
> * strcpy(av_format_context->filename, dst_filename);*
>
>
> *#ifdef _VIDEO_WRITE_ENABLED_ *
> * video_codec = avcodec_find_encoder(av_output_format->video_codec);*
> * if (!video_codec) *
> * {*
> * fprintf(stderr, "Codec not found\n");*
> * exit(5);*
> * }*
>
> * video_stream = avformat_new_stream(av_format_context, video_codec);*
> * if (!video_stream) *
> * {*
> * fprintf(stderr, "Could not alloc stream\n");*
> * exit(6);*
> * }*
>
> * avcodec_get_context_defaults3(video_stream->codec, video_codec);*
> * video_stream->codec->codec_id = AV_CODEC_ID_VP8;*
> * video_stream->codec->codec_type = AVMEDIA_TYPE_VIDEO;*
>
> * video_stream->time_base = (AVRational) {1, 30}; *
>
> * video_stream->codec->width = 640; *
> * video_stream->codec->height = 480; *
>
> * video_stream->codec->pix_fmt = PIX_FMT_YUV420P;*
> * video_stream->codec->flags |= CODEC_FLAG_GLOBAL_HEADER;*
> * video_stream->codec->bit_rate = 400000;*
> * video_stream->codec->gop_size = 10;*
> * video_stream->codec->max_b_frames=1;*
> *#endif*
>
> *#ifdef _AUDIO_WRITE_ENABLED_ *
> * audio_codec = avcodec_find_encoder(av_output_format->audio_codec);*
> * if (!audio_codec) *
> * {*
> * fprintf(stderr, "Codec not found audio codec\n");*
> * exit(5);*
> * }*
>
>
> * audio_stream = avformat_new_stream(av_format_context, audio_codec);*
> * if (!audio_stream) *
> * {*
> * fprintf(stderr, "Could not alloc stream for audio\n");*
> * exit(6);*
> * }*
>
> * avcodec_get_context_defaults3(audio_stream->codec, audio_codec);*
> * audio_stream->codec->codec_id = AV_CODEC_ID_VORBIS;*
> * audio_stream->codec->codec_type = AVMEDIA_TYPE_AUDIO;*
> * audio_stream->time_base = (AVRational) {1, 30};*
> * audio_stream->codec->sample_rate = 44100;*
> * audio_stream->codec->bit_rate = 64000;*
> * audio_stream->codec->channels = 2;*
> * audio_stream->codec->flags |= CODEC_FLAG_GLOBAL_HEADER;*
>
> *#endif*
>
> * //av_set_parameters(av_format_context);*
>
> * if(!(av_output_format->flags & AVFMT_NOFILE)) *
> * {*
> * if (avio_open(&av_format_context->pb, dst_filename,
> AVIO_FLAG_WRITE) < 0)*
> * {*
> * fprintf(stderr, "Could not open '%s'\n", dst_filename);*
> * }*
> * }*
>
> * /* Before avformat_write_header set the stream */*
> * avformat_write_header(av_format_context, NULL);*
>
> * /* initialize packet, set data to NULL, let the demuxer fill it */*
> * av_init_packet(&pkt);*
> * pkt.data = NULL;*
> * pkt.size = 0;*
>
> * //pkt.stream_index = video_stream->index;*
>
> * ret = av_read_frame(fmt_ctx, &pkt);*
> * while (ret >= 0) *
> * {*
> * index++;*
>
> * //pkt.stream_index = video_avstream->index;*
> *#ifdef _VIDEO_WRITE_ENABLED_*
> * if(pkt.stream_index == video_stream->index)*
> * {*
> * printf("Video: Read cycle %d, bytes read = %d, pkt stream
> index=%d\n", index, pkt.size, pkt.stream_index);*
> * av_write_frame(av_format_context, &pkt);*
> * }*
> *#endif*
>
>
> *#ifdef _AUDIO_WRITE_ENABLED_ *
> * if(pkt.stream_index == audio_stream->index)*
> * {*
> * pkt.flags |= AV_PKT_FLAG_KEY;*
> * printf("Audio: Read cycle %d, bytes read = %d, pkt stream
> index=%d\n", index, pkt.size, pkt.stream_index);*
> * av_write_frame(av_format_context, &pkt);*
> * }*
> *#endif *
> * av_free_packet(&pkt);*
> * ret = av_read_frame(fmt_ctx, &pkt);*
> * }*
>
> * av_write_trailer(av_format_context);*
>
> * /** Exit procedure starts */*
> * avformat_close_input(&fmt_ctx);*
> * avformat_free_context(av_format_context);*
>
> * return 0;*
>
> *}*
If I test this code with _VIDEO_WRITE_ENABLED_ defined , it is reading
input file, writes to output file. I can play output file (without sound).
If I test this code with both _VIDEO_WRITE_ENABLED_ and
_AUDIO_WRITE_ENABLED_ defined, it is crashing.
Can somebody help me to overcome this issue.
Best Regards
Austin
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