x264 num_units_in_tick can not be correctly set

Question

When I use x264 lib to encode yuv video stream,I can not set the sps parameter num_units_in_tick(i_num_units_in_tick in struct). I init the x264_param_t as :

    x264_param_t*                     m_x264Param;

    if( x264_param_default_preset( m_x264Param, "superfast", "zerolatency" ) < 0 )
    return -1;

   x264_param_apply_fastfirstpass( m_x264Param );

    /* Apply profile restrictions. */
    //baseline
    if( x264_param_apply_profile( m_x264Param, "baseline" ) < 0 )
      return -1;

The i_rc_method is set to 1. I set the parameters which decide the num_units_in_tick,then call x264_encoder_open to get x264_t .

    m_x264Param->i_timebase_den = 90000;
    m_x264Param->i_timebase_num = 3000;
    m_x264Param->i_fps_num = 60;
    m_x264Param->i_fps_den = 2;

But, num_units_in_tick is still 1, and time_scale is still 60. How can I set num_units_in_tick to 3000, so one frame occupies 3000 timestamp unit.

Answer 1

Actually, the vui_parameters have a FIELD rate, not a frame rate.

It may be that your framework is basing it on the i_fps_num instead of i_timebase_den. See if setting your FPS to 90000/3000 does what you want. Those 4 values are numerically entangled and can be specified with only two numbers.

Also, if your framework is simplifying your fractions, you're totally out of luck.