FFmpeg: cur_dts is invalid

聲明：轉帖時請註明出處

FFmpeg 版本3.0
調用ffmpeg執行轉碼時，發現會有以下打印信息：

cur_dts is invalid (this is harmless if it occurs once at the start per stream)

ffmpeg.c對應代碼以下：

/**
 * Select the output stream to process.
 *
 * @return  selected output stream, or NULL if none available
 */
static OutputStream *choose_output(void)
{
    int i;
    int64_t opts_min = INT64_MAX;
    OutputStream *ost_min = NULL;

    for (i = 0; i < nb_output_streams; i++) {
        OutputStream *ost = output_streams[i];
        int64_t opts = ost->st->cur_dts == AV_NOPTS_VALUE ? INT64_MIN :
                       av_rescale_q(ost->st->cur_dts, ost->st->time_base,
                                    AV_TIME_BASE_Q);
        if (ost->st->cur_dts == AV_NOPTS_VALUE)
            av_log(NULL, AV_LOG_DEBUG, "cur_dts is invalid (this is harmless if it occurs once at the start per stream)\n");

        if (!ost->finished && opts < opts_min) {
            opts_min = opts;
            ost_min  = ost->unavailable ? NULL : ost;
        }
    }
    return ost_min;
}

 

h264 encoder.c 初始化代碼以下：

/* Init frames. */
    if( h->param.i_bframe_adaptive == X264_B_ADAPT_TRELLIS && !h->param.rc.b_stat_read )
        h->frames.i_delay = X264_MAX(h->param.i_bframe,3)*4;
    else
        h->frames.i_delay = h->param.i_bframe;
    if( h->param.rc.b_mb_tree || h->param.rc.i_vbv_buffer_size )
        h->frames.i_delay = X264_MAX( h->frames.i_delay, h->param.rc.i_lookahead );
    i_slicetype_length = h->frames.i_delay;
    h->frames.i_delay += h->i_thread_frames - 1;
    h->frames.i_delay += h->param.i_sync_lookahead;
    h->frames.i_delay += h->param.b_vfr_input;

 

等待填滿編碼緩衝區代碼以下：

/* ------------------- Setup new frame from picture -------------------- */
    if( pic_in != NULL )
    {
        /* 1: Copy the picture to a frame and move it to a buffer */
        x264_frame_t *fenc = x264_frame_pop_unused( h, 0 );
        if( !fenc )
            return -1;

        if( x264_frame_copy_picture( h, fenc, pic_in ) < 0 )
            return -1;

        if( h->param.i_width != 16 * h->mb.i_mb_width ||
            h->param.i_height != 16 * h->mb.i_mb_height )
            x264_frame_expand_border_mod16( h, fenc );

        fenc->i_frame = h->frames.i_input++;

        if( fenc->i_frame == 0 )
            h->frames.i_first_pts = fenc->i_pts;
        if( h->frames.i_bframe_delay && fenc->i_frame == h->frames.i_bframe_delay )
            h->frames.i_bframe_delay_time = fenc->i_pts - h->frames.i_first_pts;

        if( h->param.b_vfr_input && fenc->i_pts <= h->frames.i_largest_pts )
            x264_log( h, X264_LOG_WARNING, "non-strictly-monotonic PTS\n" );

        h->frames.i_second_largest_pts = h->frames.i_largest_pts;
        h->frames.i_largest_pts = fenc->i_pts;

        if( (fenc->i_pic_struct < PIC_STRUCT_AUTO) || (fenc->i_pic_struct > PIC_STRUCT_TRIPLE) )
            fenc->i_pic_struct = PIC_STRUCT_AUTO;

        if( fenc->i_pic_struct == PIC_STRUCT_AUTO )
        {
#if HAVE_INTERLACED
            int b_interlaced = fenc->param ? fenc->param->b_interlaced : h->param.b_interlaced;
#else
            int b_interlaced = 0;
#endif
            if( b_interlaced )
            {
                int b_tff = fenc->param ? fenc->param->b_tff : h->param.b_tff;
                fenc->i_pic_struct = b_tff ? PIC_STRUCT_TOP_BOTTOM : PIC_STRUCT_BOTTOM_TOP;
            }
            else
                fenc->i_pic_struct = PIC_STRUCT_PROGRESSIVE;
        }

        if( h->param.rc.b_mb_tree && h->param.rc.b_stat_read )
        {
            if( x264_macroblock_tree_read( h, fenc, pic_in->prop.quant_offsets ) )
                return -1;
        }
        else
            x264_stack_align( x264_adaptive_quant_frame, h, fenc, pic_in->prop.quant_offsets );

        if( pic_in->prop.quant_offsets_free )
            pic_in->prop.quant_offsets_free( pic_in->prop.quant_offsets );

        if( h->frames.b_have_lowres )
            x264_frame_init_lowres( h, fenc );

        /* 2: Place the frame into the queue for its slice type decision */
        x264_lookahead_put_frame( h, fenc );

        if( h->frames.i_input <= h->frames.i_delay + 1 - h->i_thread_frames )
        {
            /* Nothing yet to encode, waiting for filling of buffers */
            pic_out->i_type = X264_TYPE_AUTO;
            return 0;
        }
    }
    else
    {
        /* signal kills for lookahead thread */
        x264_pthread_mutex_lock( &h->lookahead->ifbuf.mutex );
        h->lookahead->b_exit_thread = 1;
        x264_pthread_cond_broadcast( &h->lookahead->ifbuf.cv_fill );
        x264_pthread_mutex_unlock( &h->lookahead->ifbuf.mutex );
    }

 

以視頻h264編碼爲例，該打印的數量與輸出編碼幀的時間有關：

bframes ： consecutive B-frames before this P-frame

i_lookahead： Number of frames for frametype lookahead

i_thread_frames：/* Number of different frames being encoded by threads;
                                      * 1 when sliced-threads is on. */

i_sync_lookahead;  /* threaded lookahead buffer */

b_vfr_input;            /* VFR input.  If 1, use timebase and timestamps for ratecontrol purposes.
                                 * If 0, use fps only. */

 

ffmpeg命令行：

./ffmpeg -i test_2.flv -vcodec libx264 -r 10 -report -y -f flv test_2out.flv

 

x264 encoder.c中添加打印語句以下：

/* Init frames. */
    if( h->param.i_bframe_adaptive == X264_B_ADAPT_TRELLIS && !h->param.rc.b_stat_read )
        h->frames.i_delay = X264_MAX(h->param.i_bframe,3)*4;
    else
        h->frames.i_delay = h->param.i_bframe;
    x264_log( h, X264_LOG_DEBUG,"X264 init1 delay:%d\n",h->frames.i_delay);
    if( h->param.rc.b_mb_tree || h->param.rc.i_vbv_buffer_size )
        h->frames.i_delay = X264_MAX( h->frames.i_delay, h->param.rc.i_lookahead );
    x264_log( h, X264_LOG_DEBUG,"X264 init2 delay:%d\n",h->frames.i_delay);
    i_slicetype_length = h->frames.i_delay;
    h->frames.i_delay += h->i_thread_frames - 1;
    x264_log( h, X264_LOG_DEBUG,"X264 init3 delay:%d\n",h->frames.i_delay);
    h->frames.i_delay += h->param.i_sync_lookahead;
    x264_log( h, X264_LOG_DEBUG,"X264 init4 delay:%d\n",h->frames.i_delay);
    h->frames.i_delay += h->param.b_vfr_input;
    x264_log( h, X264_LOG_DEBUG,"X264 init5 delay:%d\n",h->frames.i_delay);

打印日誌：

[libx264 @ 0x335a580] X264 init1 delay:3
[libx264 @ 0x335a580] X264 init2 delay:40
[libx264 @ 0x335a580] X264 init3 delay:40
[libx264 @ 0x335a580] X264 init4 delay:40
[libx264 @ 0x335a580] X264 init5 delay:41

 

總結：

cur_dts is invalid (this is harmless if it occurs once at the start per stream) 打印信息與編碼輸出幀的延時有關，其中最主要與i_lookahead值有關。

當編碼器有幀輸出時，則不會出現該打印信息。

以下圖所示，解碼41幀後，第42幀開始進行編碼。

 

[libx264 @ 0x335a580] x264 frame info........
[libx264 @ 0x335a580] x264 frame encoder info........
[libx264 @ 0x335a580] X264 input frame:41, delay frame:41, thread frame:1
[libx264 @ 0x335a580] x264 frame encoder finish........
choose_output, OutputStream stream cur_dts:0 ...
cur_dts is invalid (this is harmless if it occurs once at the start per stream)
choose_output, OutputStream stream cur_dts:3864 ...
OutputStream filter is true ...
process input, file index0, ...
choose_output, OutputStream stream cur_dts:0 ...
cur_dts is invalid (this is harmless if it occurs once at the start per stream)
choose_output, OutputStream stream cur_dts:3890 ...
OutputStream filter is true ...
process input, file index0, ...
choose_output, OutputStream stream cur_dts:0 ...
cur_dts is invalid (this is harmless if it occurs once at the start per stream)
choose_output, OutputStream stream cur_dts:3917 ...
OutputStream filter is true ...
process input, file index0, ...
choose_output, OutputStream stream cur_dts:0 ...
cur_dts is invalid (this is harmless if it occurs once at the start per stream)
choose_output, OutputStream stream cur_dts:3943 ...
OutputStream filter is true ...
process input, file index0, ...
[h264 @ 0x3355260] decoding video .......
[libx264 @ 0x335a580] x264 frame info........
[libx264 @ 0x335a580] x264 frame encoder info........
[libx264 @ 0x335a580] X264 input frame:42, delay frame:41, thread frame:1
[libx264 @ 0x335a580] frame=   0 QP=2.40 NAL=3 Slice:I Poc:0   I:1064 P:0    SKIP:0    size=1086 bytes
[libx264 @ 0x335a580] x264 frame encoder finish........
[flv @ 0x3263460] flv enc type:0, dts:0 pts:200
choose_output, OutputStream stream cur_dts:-100 ..

註釋：

libx264庫在添加打印後，須要進行編譯和安裝，即make && make install

此外，ffmpeg也須要配置，編譯和安裝，才能使打印信息生效。