Remux RTSP stream into container? (Write read frame without decoding it) - c

Question

I'm trying to use dranger tutorials for writing a RTSP h264 streamed video directly to a file without decoding and encoding it (ffmpeg 3.0/3.1 library). But I'm a bit lost on how do I need to populate the AVFormatContext pointer for the av_write_frame once I get the corresponding AVPacket.
Trying to clarify. What I want to do is this
1. Open webcam stream in h264
2. Read a frame
3. Save it to a file without decoding and encoding it.
EDIT: I've also tried to use the remuxing example in ffmpeg's documentation (doing a network init()) but I'm getting dts and pts sync errors when going from rtsp -> .mp4
Copy pasting the code from the tutorial:
#include <stdio.h>
#include <libavutil/pixfmt.h>
#include <libavcodec/avcodec.h>
#include <libavutil/avconfig.h>
#include <libswscale/swscale.h>
#include <libavformat/avformat.h>
int main(int argc, char *argv[]) {
av_register_all();
avcodec_register_all();
avformat_network_init();
AVFormatContext *pFormatCtx = avformat_alloc_context();
// Camera comes from argv[1]
avformat_open_input(&pFormatCtx, argv[1], NULL, NULL);
avformat_find_stream_info(pFormatCtx, NULL);
av_dump_format(pFormatCtx, 0, argv[1], 0);
int video_stream_idx = -1;
for (int i = 0; i < pFormatCtx->nb_streams; i++) {
if (pFormatCtx->streams[i]->codecpar->codec_type == AVMEDIA_TYPE_VIDEO) {
video_stream_idx = i;
break;
}
}
AVCodecContext *pCodecContext = NULL;
AVCodecContext *pCodecContextOrig = NULL;
pCodecContextOrig = pFormatCtx->streams[video_stream_idx]->codec;
AVCodec *pCodec;
pCodec = avcodec_find_decoder(pCodecContextOrig->codec_id);
pCodecContext = avcodec_alloc_context3(pCodec);
avcodec_copy_context(pCodecContext, pCodecContextOrig);
avcodec_open2(pCodecContext, pCodec, NULL);
AVFrame *pFrame = av_frame_alloc();
AVFrame *pFrameRGB = av_frame_alloc();
uint8_t *buffer = NULL;
int buffer_size = avpicture_get_size(AV_PIX_FMT_RGB24, pCodecContext->width,
pCodecContext->height);
buffer = (uint8_t *)av_malloc(buffer_size * sizeof(uint8_t));
// fill buffer
avpicture_fill((AVPicture *)pFrameRGB, buffer, AV_PIX_FMT_RGB24,
pCodecContext->width, pCodecContext->height);
struct SwsContext *sws_ctx = NULL;
int frame_finished = 0;
AVPacket packet;
// Size(src), fmt(src), Size(dst), fmt(dst) .. flags
sws_ctx = sws_getContext(pCodecContext->width, pCodecContext->height,
pCodecContext->pix_fmt, pCodecContext->width,
pCodecContext->height, AV_PIX_FMT_RGB24,
SWS_BILINEAR, NULL, NULL, NULL);
AVFormatContext *out_fmt_ctx;
avformat_write_header(out_fmt_ctx, NULL);
int i = 0;
while (i < 100 && (av_read_frame(pFormatCtx, &packet) >= 0)) {
// Want to write these frames to disk
i++;
}
av_write_trailer(out_fmt_ctx);
av_free(buffer);
av_free(pFrameRGB);
av_free(pFrame);
avcodec_close(pCodecContext);
avcodec_close(pCodecContextOrig);
avformat_close_input(&pFormatCtx);
return 0;
}
I think a lot of stuff of this code can be removed. I'm trying to learn :).
Linking against -lavutil -lavformat -lavcodec -lz -lavutil -lm -lswscale

Answer 1

I fixed by using the remuxing.c example from FFmpeg's documentation. The problem was that for some reason (I still dont know why) the first packet dts and pts was higher than the second (and following ones, which increased monotonically). Fixed it by skipping the first packet write :).