while (!av_read_frame(fmt_ctx, &pkt)) {
if (selected_streams[pkt.stream_index]) {
AVRational tb = fmt_ctx->streams[pkt.stream_index]->time_base;
while (!av_read_frame(fmt_ctx, &pkt)) {
if (selected_streams[pkt.stream_index]) {
AVRational tb = fmt_ctx->streams[pkt.stream_index]->time_base;