这是x264中的函数，请对每一行代码做注释static int encode( x264_param_t *param, cli_opt_t *opt )
{
    x264_t *h = NULL;
    x264_picture_t pic;
    cli_pic_t cli_pic;
    const cli_pulldown_t *pulldown = NULL; // shut up gcc

    int     i_frame = 0;
    int     i_frame_output = 0;
    int64_t i_end, i_previous = 0, i_start = 0;
    int64_t i_file = 0;
    int     i_frame_size;
    int64_t last_dts = 0;
    int64_t prev_dts = 0;
    int64_t first_dts = 0;
#   define  MAX_PTS_WARNING 3 /* arbitrary */
    int     pts_warning_cnt = 0;
    int64_t largest_pts = -1;
    int64_t second_largest_pts = -1;
    int64_t ticks_per_frame;
    double  duration;
    double  pulldown_pts = 0;
    int     retval = 0;

    opt->b_progress &= param->i_log_level < X264_LOG_DEBUG;

    /* set up pulldown */
    // 设置了pulldown并且没有设置变帧率
    if( opt->i_pulldown && !param->b_vfr_input )
    {
        param->b_pulldown = 1;
        param->b_pic_struct = 1;
        pulldown = &pulldown_values[opt->i_pulldown];
        param->i_timebase_num = param->i_fps_den;
        FAIL_IF_ERROR2( fmod( param->i_fps_num * pulldown->fps_factor, 1 ),
                        "unsupported framerate for chosen pulldown\n" );
        param->i_timebase_den = param->i_fps_num * pulldown->fps_factor;
    }

    h = x264_encoder_open( param );
    FAIL_IF_ERROR2( !h, "x264_encoder_open failed\n" );

    x264_encoder_parameters( h, param );

    FAIL_IF_ERROR2( cli_output.set_param( opt->hout, param ), "can't set outfile param\n" );

    i_start = x264_mdate();

    /* ticks/frame = ticks/second / frames/second */
    ticks_per_frame = (int64_t)param->i_timebase_den * param->i_fps_den / param->i_timebase_num / param->i_fps_num;
    FAIL_IF_ERROR2( ticks_per_frame < 1 && !param->b_vfr_input, "ticks_per_frame invalid: %"PRId64"\n", ticks_per_frame );
    ticks_per_frame = X264_MAX( ticks_per_frame, 1 );

    if( !param->b_repeat_headers )
    {
        // Write SPS/PPS/SEI
        x264_nal_t *headers;
        int i_nal;

        FAIL_IF_ERROR2( x264_encoder_headers( h, &headers, &i_nal ) < 0, "x264_encoder_headers failed\n" );
        FAIL_IF_ERROR2( (i_file = cli_output.write_headers( opt->hout, headers )) < 0, "error writing headers to output file\n" );
    }

    if( opt->tcfile_out )
        fprintf( opt->tcfile_out, "# timecode format v2\n" );

    /* Encode frames */
    for( ; !b_ctrl_c && (i_frame < param->i_frame_total || !param->i_frame_total); i_frame++ )
    {
        if( filter.get_frame( opt->hin, &cli_pic, i_frame + opt->i_seek ) )
            break;
        x264_picture_init( &pic );
        convert_cli_to_lib_pic( &pic, &cli_pic );

        if( !param->b_vfr_input )
            pic.i_pts = i_frame;

        if( opt->i_pulldown && !param->b_vfr_input )
        {
            pic.i_pic_struct = pulldown->pattern[ i_frame % pulldown->mod ];
            pic.i_pts = (int64_t)( pulldown_pts + 0.5 );
            pulldown_pts += pulldown_frame_duration[pic.i_pic_struct];
        }
        else if( opt->timebase_convert_multiplier )
            pic.i_pts = (int64_t)( pic.i_pts * opt->timebase_convert_multiplier + 0.5 );

        if( pic.i_pts <= largest_pts )
        {
            if( cli_log_level >= X264_LOG_DEBUG || pts_warning_cnt < MAX_PTS_WARNING )
                x264_cli_log( "x264", X264_LOG_WARNING, "non-strictly-monotonic pts at frame %d (%"PRId64" <= %"PRId64")\n",
                             i_frame, pic.i_pts, largest_pts );
            else if( pts_warning_cnt == MAX_PTS_WARNING )
                x264_cli_log( "x264", X264_LOG_WARNING, "too many nonmonotonic pts warnings, suppressing further ones\n" );
            pts_warning_cnt++;
            pic.i_pts = largest_pts + ticks_per_frame;
        }

        second_largest_pts = largest_pts;
        largest_pts = pic.i_pts;
        if( opt->tcfile_out )
            fprintf( opt->tcfile_out, "%.6f\n", pic.i_pts * ((double)param->i_timebase_num / param->i_timebase_den) * 1e3 );

        if( opt->qpfile )
            parse_qpfile( opt, &pic, i_frame + opt->i_seek );

        prev_dts = last_dts;
        i_frame_size = encode_frame( h, opt->hout, &pic, &last_dts );
        if( i_frame_size < 0 )
        {
            b_ctrl_c = 1; /* lie to exit the loop */
            retval = -1;
        }
        else if( i_frame_size )
        {
            i_file += i_frame_size;
            i_frame_output++;
            if( i_frame_output == 1 )
                first_dts = prev_dts = last_dts;
        }

        if( filter.release_frame( opt->hin, &cli_pic, i_frame + opt->i_seek ) )
            break;

        /* update status line (up to 1000 times per input file) */
        if( opt->b_progress && i_frame_output )
            i_previous = print_status( i_start, i_previous, i_frame_output, param->i_frame_total, i_file, param, 2 * last_dts - prev_dts - first_dts );
    }
    /* Flush delayed frames */
    while( !b_ctrl_c && x264_encoder_delayed_frames( h ) )
    {
        prev_dts = last_dts;
        i_frame_size = encode_frame( h, opt->hout, NULL, &last_dts );
        if( i_frame_size < 0 )
        {
            b_ctrl_c = 1; /* lie to exit the loop */
            retval = -1;
        }
        else if( i_frame_size )
        {
            i_file += i_frame_size;
            i_frame_output++;
            if( i_frame_output == 1 )
                first_dts = prev_dts = last_dts;
        }
        if( opt->b_progress && i_frame_output )
            i_previous = print_status( i_start, i_previous, i_frame_output, param->i_frame_total, i_file, param, 2 * last_dts - prev_dts - first_dts );
    }
fail:
    if( pts_warning_cnt >= MAX_PTS_WARNING && cli_log_level < X264_LOG_DEBUG )
        x264_cli_log( "x264", X264_LOG_WARNING, "%d suppressed nonmonotonic pts warnings\n", pts_warning_cnt-MAX_PTS_WARNING );

    /* duration algorithm fails when only 1 frame is output */
    if( i_frame_output == 1 )
        duration = (double)param->i_fps_den / param->i_fps_num;
    else if( b_ctrl_c )
        duration = (double)(2 * last_dts - prev_dts - first_dts) * param->i_timebase_num / param->i_timebase_den;
    else
        duration = (double)(2 * largest_pts - second_largest_pts) * param->i_timebase_num / param->i_timebase_den;

    i_end = x264_mdate();
    /* Erase progress indicator before printing encoding stats. */
    if( opt->b_progress )
        fprintf( stderr, "                                                                               \r" );
    if( h )
        x264_encoder_close( h );
    fprintf( stderr, "\n" );

    if( b_ctrl_c )
        fprintf( stderr, "aborted at input frame %d, output frame %d\n", opt->i_seek + i_frame, i_frame_output );

    cli_output.close_file( opt->hout, largest_pts, second_largest_pts );
    opt->hout = NULL;

    if( i_frame_output > 0 )
    {
        double fps = (double)i_frame_output * (double)1000000 /
                     (double)( i_end - i_start );

        fprintf( stderr, "encoded %d frames, %.2f fps, %.2f kb/s\n", i_frame_output, fps,
                 (double) i_file * 8 / ( 1000 * duration ) );
    }

    return retval;
}