FFmpeg remux without decode/encode - ffmpeg

Question

I want to use ffmpeg lib to save rtsp stream to local mp4 file without decode.
both the inpout stream and output file use H264+AAC codec.
For now I use the following code to read the packet from the input stream and write to the output file.
...
av_write_header(oFmtCtx);
av_init_packet(&packet);
int j = 0;
while (av_read_frame(pIFmtCtx, &packet) >= 0 && j < 140/*temp use to get a period of the stream*/)
{
//now I only output the audio stream
if (packet.stream_index == audioStream)
{
AVPacket pkt;
av_init_packet(&pkt);
pkt.size = packet.size;
pkt.data = packet.data;
pkt.dts = AV_NOPTS_VALUE;
pkt.pts = AV_NOPTS_VALUE;
pkt.flags |= PKT_FLAG_KEY;
pkt.stream_index = oStream->index;
if (av_interleaved_write_frame(oFmtCtx, &pkt) != 0)
{
LOGI("Error while writing audio frame\n");
break;
}
}
j++;
}
av_write_trailer(oFmtCtx);
The file is generated. and when I open it using VLC, the playback lasts for the right time but no audio is outputed.
Any help will be greatly appreciated, Thanks in advance.
Bolton

Answer 1

Finally I made it. Below is my code:
while (j < 140)
{
av_read_frame(pIFmtCtx, &packet);
pkt_stream_index = packet.stream_index;
pkt_pts = packet.pts;
pkt_dts = packet.dts;
if (packet.stream_index == audioStream)
{
packet.stream_index = oStream->index;
av_write_frame(oFmtCtx, &packet);
packet.stream_index = pkt_stream_index;
packet.pts = pkt_pts;
packet.dts = pkt_dts;
}
av_free_packet(&packet);
j++;
}
I don't know the reason but it works!