FFmpeg版本：3.4

在FFmpeg中，每一种文件容器格式都对应一种AVInputFormat 结构，位于源码中libavformat文件夹中。当调用avformat_open_input的时候，FFmpeg会根据媒体封装格式的特点(主要是根据AVInputFormat结构的read_probe函数根据传入的一段buffer来判断传入的文件是否能被解析为该AVInputFormat对应的容器格式)，对全部已知的格式进行判断并设置一个分值，取其中最高的分值来关联到一种文件容器格式。

我们通过下面的函数调用堆栈信息来分析avformat_open_input是怎样一步步的关联到具体的文件容器格式的。

static int init_input(AVFormatContext *s, const char *filename,
                      AVDictionary **options)
{
    //...
    return av_probe_input_buffer2(s->pb, &s->iformat, filename,
                                 s, 0, s->format_probesize);
}

int av_probe_input_buffer2(AVIOContext *pb, AVInputFormat **fmt,
                          const char *filename, void *logctx,
                          unsigned int offset, unsigned int max_probe_size)
{
    //...
    //把AVFormatContext和具体的AVInputFormat联系起来了
     *fmt = av_probe_input_format2(&pd, 1, &score);
    //...
}

FFmpeg中实现探测的函数是av_probe_input_buffer2和av_probe_input_format3。其核心代码如下：

//遍历所有的Demuxer
while ((fmt1 = av_demuxer_iterate(&i))) {
        if (!is_opened == !(fmt1->flags & AVFMT_NOFILE) && strcmp(fmt1->name, "image2"))
            continue;
        score = 0;
        if (fmt1->read_probe) {
            score = fmt1->read_probe(&lpd);
            if (score)
                av_log(NULL, AV_LOG_TRACE, "Probing %s score:%d size:%d\n", fmt1->name, score, lpd.buf_size);
            if (fmt1->extensions && av_match_ext(lpd.filename, fmt1->extensions)) {
                switch (nodat) {
                case NO_ID3:
                    score = FFMAX(score, 1);
                    break;
                case ID3_GREATER_PROBE:
                case ID3_ALMOST_GREATER_PROBE:
                    score = FFMAX(score, AVPROBE_SCORE_EXTENSION / 2 - 1);
                    break;
                case ID3_GREATER_MAX_PROBE:
                    score = FFMAX(score, AVPROBE_SCORE_EXTENSION);
                    break;
                }
            }
        } else if (fmt1->extensions) {
            if (av_match_ext(lpd.filename, fmt1->extensions))
                score = AVPROBE_SCORE_EXTENSION;
        }
        if (av_match_name(lpd.mime_type, fmt1->mime_type)) {
            if (AVPROBE_SCORE_MIME > score) {
                av_log(NULL, AV_LOG_DEBUG, "Probing %s score:%d increased to %d due to MIME type\n", fmt1->name, score, AVPROBE_SCORE_MIME);
                score = AVPROBE_SCORE_MIME;
            }
        }
        if (score > score_max) {
            score_max = score;
            fmt       = (AVInputFormat*)fmt1;
        } else if (score == score_max)
            fmt = NULL;
    }

上面代码的原理就是优先使用demuxer的read_probe函数，然后参考文件名的后缀名来关联某个AVInputFormat。

const AVInputFormat *av_demuxer_iterate(void **opaque)
{
    static const uintptr_t size = sizeof(demuxer_list)/sizeof(demuxer_list[0]) - 1;
    uintptr_t i = (uintptr_t)*opaque;
    const AVInputFormat *f = NULL;

    if (i < size) {
        //遍历demuxer_list中的所有demuxer
        f = demuxer_list[i];
    } else if (outdev_list) {
        f = indev_list[i - size];
    }

    if (f)
        *opaque = (void*)(i + 1);
    return f;
}

demuxer_list数组定义在libavformat/demuxer_list.c中，该文件是编译FFMPEGconfigure的时候生成的

print_enabled_components libavformat/demuxer_list.c AVInputFormat demuxer_list $DEMUXER_LIST

static const AVInputFormat * const demuxer_list[] = {
    &ff_aa_demuxer,
    &ff_aac_demuxer,
    &ff_ac3_demuxer,
    &ff_acm_demuxer,
    &ff_act_demuxer,
    &ff_adf_demuxer,
    &ff_adp_demuxer,
    &ff_ads_demuxer,
    &ff_adx_demuxer,
    &ff_aea_demuxer,
    &ff_afc_demuxer,
    &ff_aiff_demuxer,
    &ff_aix_demuxer,
    &ff_amr_demuxer,
    &ff_amrnb_demuxer,
    &ff_amrwb_demuxer,
    &ff_anm_demuxer,
    &ff_apc_demuxer,
    &ff_ape_demuxer,
    &ff_apng_demuxer,
    &ff_aptx_demuxer,
    &ff_aptx_hd_demuxer,
    &ff_aqtitle_demuxer,
    &ff_asf_demuxer,
    &ff_asf_o_demuxer,
    &ff_ass_demuxer,
    &ff_ast_demuxer,
    &ff_au_demuxer,
    &ff_avi_demuxer,
    &ff_avr_demuxer,
    &ff_avs_demuxer,
    &ff_bethsoftvid_demuxer,
    &ff_bfi_demuxer,
    &ff_bintext_demuxer,
    &ff_bink_demuxer,
    &ff_bit_demuxer,
    &ff_bmv_demuxer,
    &ff_bfstm_demuxer,
    &ff_brstm_demuxer,
    &ff_boa_demuxer,
    &ff_c93_demuxer,
    &ff_caf_demuxer,
    &ff_cavsvideo_demuxer,
    &ff_cdg_demuxer,
    &ff_cdxl_demuxer,
    &ff_cine_demuxer,
    &ff_codec2_demuxer,
    &ff_codec2raw_demuxer,
    &ff_concat_demuxer,
    &ff_data_demuxer,
    &ff_daud_demuxer,
    &ff_dcstr_demuxer,
    &ff_dfa_demuxer,
    &ff_dirac_demuxer,
    &ff_dnxhd_demuxer,
    &ff_dsf_demuxer,
    &ff_dsicin_demuxer,
    &ff_dss_demuxer,
    &ff_dts_demuxer,
    &ff_dtshd_demuxer,
    &ff_dv_demuxer,
    &ff_dvbsub_demuxer,
    &ff_dvbtxt_demuxer,
    &ff_dxa_demuxer,
    &ff_ea_demuxer,
    &ff_ea_cdata_demuxer,
    &ff_eac3_demuxer,
    &ff_epaf_demuxer,
    &ff_ffmetadata_demuxer,
    &ff_filmstrip_demuxer,
    &ff_fits_demuxer,
    &ff_flac_demuxer,
    &ff_flic_demuxer,
    &ff_flv_demuxer,
    &ff_live_flv_demuxer,
    &ff_fourxm_demuxer,
    &ff_frm_demuxer,
    &ff_fsb_demuxer,
    &ff_g722_demuxer,
    &ff_g723_1_demuxer,
    &ff_g726_demuxer,
    &ff_g726le_demuxer,
    &ff_g729_demuxer,
    &ff_gdv_demuxer,
    &ff_genh_demuxer,
    &ff_gif_demuxer,
    &ff_gsm_demuxer,
    &ff_gxf_demuxer,
    &ff_h261_demuxer,
    &ff_h263_demuxer,
    &ff_h264_demuxer,
    &ff_hevc_demuxer,
    &ff_hls_demuxer,
    &ff_hnm_demuxer,
    &ff_ico_demuxer,
    &ff_idcin_demuxer,
    &ff_idf_demuxer,
    &ff_iff_demuxer,
    &ff_ilbc_demuxer,
    &ff_image2_demuxer,
    &ff_image2pipe_demuxer,
    &ff_image2_alias_pix_demuxer,
    &ff_image2_brender_pix_demuxer,
    &ff_ingenient_demuxer,
    &ff_ipmovie_demuxer,
    &ff_ircam_demuxer,
    &ff_iss_demuxer,
    &ff_iv8_demuxer,
    &ff_ivf_demuxer,
    &ff_ivr_demuxer,
    &ff_jacosub_demuxer,
    &ff_jv_demuxer,
    &ff_lmlm4_demuxer,
    &ff_loas_demuxer,
    &ff_lrc_demuxer,
    &ff_lvf_demuxer,
    &ff_lxf_demuxer,
    &ff_m4v_demuxer,
    &ff_matroska_demuxer,
    &ff_mgsts_demuxer,
    &ff_microdvd_demuxer,
    &ff_mjpeg_demuxer,
    &ff_mjpeg_2000_demuxer,
    &ff_mlp_demuxer,
    &ff_mlv_demuxer,
    &ff_mm_demuxer,
    &ff_mmf_demuxer,
    &ff_mov_demuxer,
    &ff_mp3_demuxer,
    &ff_mpc_demuxer,
    &ff_mpc8_demuxer,
    &ff_mpegps_demuxer,
    &ff_mpegts_demuxer,
    &ff_mpegtsraw_demuxer,
    &ff_mpegvideo_demuxer,
    &ff_mpjpeg_demuxer,
    &ff_mpl2_demuxer,
    &ff_mpsub_demuxer,
    &ff_msf_demuxer,
    &ff_msnwc_tcp_demuxer,
    &ff_mtaf_demuxer,
    &ff_mtv_demuxer,
    &ff_musx_demuxer,
    &ff_mv_demuxer,
    &ff_mvi_demuxer,
    &ff_mxf_demuxer,
    &ff_mxg_demuxer,
    &ff_nc_demuxer,
    &ff_nistsphere_demuxer,
    &ff_nsp_demuxer,
    &ff_nsv_demuxer,
    &ff_nut_demuxer,
    &ff_nuv_demuxer,
    &ff_ogg_demuxer,
    &ff_oma_demuxer,
    &ff_paf_demuxer,
    &ff_pcm_alaw_demuxer,
    &ff_pcm_mulaw_demuxer,
    &ff_pcm_f64be_demuxer,
    &ff_pcm_f64le_demuxer,
    &ff_pcm_f32be_demuxer,
    &ff_pcm_f32le_demuxer,
    &ff_pcm_s32be_demuxer,
    &ff_pcm_s32le_demuxer,
    &ff_pcm_s24be_demuxer,
    &ff_pcm_s24le_demuxer,
    &ff_pcm_s16be_demuxer,
    &ff_pcm_s16le_demuxer,
    &ff_pcm_s8_demuxer,
    &ff_pcm_u32be_demuxer,
    &ff_pcm_u32le_demuxer,
    &ff_pcm_u24be_demuxer,
    &ff_pcm_u24le_demuxer,
    &ff_pcm_u16be_demuxer,
    &ff_pcm_u16le_demuxer,
    &ff_pcm_u8_demuxer,
    &ff_pjs_demuxer,
    &ff_pmp_demuxer,
    &ff_pva_demuxer,
    &ff_pvf_demuxer,
    &ff_qcp_demuxer,
    &ff_r3d_demuxer,
    &ff_rawvideo_demuxer,
    &ff_realtext_demuxer,
    &ff_redspark_demuxer,
    &ff_rl2_demuxer,
    &ff_rm_demuxer,
    &ff_roq_demuxer,
    &ff_rpl_demuxer,
    &ff_rsd_demuxer,
    &ff_rso_demuxer,
    &ff_rtp_demuxer,
    &ff_rtsp_demuxer,
    &ff_s337m_demuxer,
    &ff_sami_demuxer,
    &ff_sap_demuxer,
    &ff_sbc_demuxer,
    &ff_sbg_demuxer,
    &ff_scc_demuxer,
    &ff_sdp_demuxer,
    &ff_sdr2_demuxer,
    &ff_sds_demuxer,
    &ff_sdx_demuxer,
    &ff_segafilm_demuxer,
    &ff_shorten_demuxer,
    &ff_siff_demuxer,
    &ff_sln_demuxer,
    &ff_smacker_demuxer,
    &ff_smjpeg_demuxer,
    &ff_smush_demuxer,
    &ff_sol_demuxer,
    &ff_sox_demuxer,
    &ff_spdif_demuxer,
    &ff_srt_demuxer,
    &ff_str_demuxer,
    &ff_stl_demuxer,
    &ff_subviewer1_demuxer,
    &ff_subviewer_demuxer,
    &ff_sup_demuxer,
    &ff_svag_demuxer,
    &ff_swf_demuxer,
    &ff_tak_demuxer,
    &ff_tedcaptions_demuxer,
    &ff_thp_demuxer,
    &ff_threedostr_demuxer,
    &ff_tiertexseq_demuxer,
    &ff_tmv_demuxer,
    &ff_truehd_demuxer,
    &ff_tta_demuxer,
    &ff_txd_demuxer,
    &ff_tty_demuxer,
    &ff_ty_demuxer,
    &ff_v210_demuxer,
    &ff_v210x_demuxer,
    &ff_vag_demuxer,
    &ff_vc1_demuxer,
    &ff_vc1t_demuxer,
    &ff_vivo_demuxer,
    &ff_vmd_demuxer,
    &ff_vobsub_demuxer,
    &ff_voc_demuxer,
    &ff_vpk_demuxer,
    &ff_vplayer_demuxer,
    &ff_vqf_demuxer,
    &ff_w64_demuxer,
    &ff_wav_demuxer,
    &ff_wc3_demuxer,
    &ff_webm_dash_manifest_demuxer,
    &ff_webvtt_demuxer,
    &ff_wsaud_demuxer,
    &ff_wsd_demuxer,
    &ff_wsvqa_demuxer,
    &ff_wtv_demuxer,
    &ff_wve_demuxer,
    &ff_wv_demuxer,
    &ff_xa_demuxer,
    &ff_xbin_demuxer,
    &ff_xmv_demuxer,
    &ff_xvag_demuxer,
    &ff_xwma_demuxer,
    &ff_yop_demuxer,
    &ff_yuv4mpegpipe_demuxer,
    &ff_image_bmp_pipe_demuxer,
    &ff_image_dds_pipe_demuxer,
    &ff_image_dpx_pipe_demuxer,
    &ff_image_exr_pipe_demuxer,
    &ff_image_j2k_pipe_demuxer,
    &ff_image_jpeg_pipe_demuxer,
    &ff_image_jpegls_pipe_demuxer,
    &ff_image_pam_pipe_demuxer,
    &ff_image_pbm_pipe_demuxer,
    &ff_image_pcx_pipe_demuxer,
    &ff_image_pgmyuv_pipe_demuxer,
    &ff_image_pgm_pipe_demuxer,
    &ff_image_pictor_pipe_demuxer,
    &ff_image_png_pipe_demuxer,
    &ff_image_ppm_pipe_demuxer,
    &ff_image_psd_pipe_demuxer,
    &ff_image_qdraw_pipe_demuxer,
    &ff_image_sgi_pipe_demuxer,
    &ff_image_svg_pipe_demuxer,
    &ff_image_sunrast_pipe_demuxer,
    &ff_image_tiff_pipe_demuxer,
    &ff_image_webp_pipe_demuxer,
    &ff_image_xpm_pipe_demuxer,
    &ff_image_xwd_pipe_demuxer,
    NULL };

read_probe实现

一般probe有两种情况。

对于在文件开头存在特征码的封装格式，比如avi、rm/rmvb、flv、mkv、asf可以直接使用特征码。

AVI的特征码是RIFF AVI，下面是FFmpeg中的avi探测函数实现：

//libavformat/avidec.c
static const char avi_headers[][8] = {
    { 'R', 'I', 'F', 'F', 'A', 'V', 'I', ' '  },
    { 'R', 'I', 'F', 'F', 'A', 'V', 'I', 'X'  },
    { 'R', 'I', 'F', 'F', 'A', 'V', 'I', 0x19 },
    { 'O', 'N', '2', ' ', 'O', 'N', '2', 'f'  },
    { 'R', 'I', 'F', 'F', 'A', 'M', 'V', ' '  },
    { 0 }
};
static int avi_probe(AVProbeData *p)
{
    int i;

    /* check file header */
    for (i = 0; avi_headers[i][0]; i++)
        if (AV_RL32(p->buf    ) == AV_RL32(avi_headers[i]    ) &&
            AV_RL32(p->buf + 8) == AV_RL32(avi_headers[i] + 4))
            return AVPROBE_SCORE_MAX;

    return 0;
}

rm/rmvb文件的特征码是.RMF、.ra，下面是FFmpeg中rm探测函数：

//libavformat/rmdec.c
static int rm_probe(AVProbeData *p)
{
    /* check file header */
    if ((p->buf[0] == '.' && p->buf[1] == 'R' &&
         p->buf[2] == 'M' && p->buf[3] == 'F' &&
         p->buf[4] == 0 && p->buf[5] == 0) ||
        (p->buf[0] == '.' && p->buf[1] == 'r' &&
         p->buf[2] == 'a' && p->buf[3] == 0xfd))
        return AVPROBE_SCORE_MAX;
    else
        return 0;
}

flv文件的特征码是FLV，下面是FFmpeg中flv探测函数：

//libavformat/flvdec.c
static int probe(AVProbeData *p, int live)
{
    const uint8_t *d = p->buf;
    unsigned offset = AV_RB32(d + 5);

    if (d[0] == 'F' &&
        d[1] == 'L' &&
        d[2] == 'V' &&
        d[3] < 5 && d[5] == 0 &&
        offset + 100 < p->buf_size &&
        offset > 8) {
        int is_live = !memcmp(d + offset + 40, "NGINX RTMP", 10);

        if (live == is_live)
            return AVPROBE_SCORE_MAX;
    }
    return 0;
}

static int flv_probe(AVProbeData *p)
{
    return probe(p, 0);
}

mkv的特征码就是EBML_Header_ID和已知的DocType，下面是FFmpeg的mkv探测函数：

//libavformat/matroskadec.c
/* top-level master-IDs */
#define EBML_ID_HEADER             0x1A45DFA3
static int matroska_probe(AVProbeData *p)
{
    uint64_t total = 0;
    int len_mask = 0x80, size = 1, n = 1, i;

    /* EBML header? */
    if (AV_RB32(p->buf) != EBML_ID_HEADER)
        return 0;

    /* length of header */
    total = p->buf[4];
    while (size <= 8 && !(total & len_mask)) {
        size++;
        len_mask >>= 1;
    }
    if (size > 8)
        return 0;
    total &= (len_mask - 1);
    while (n < size)
        total = (total << 8) | p->buf[4 + n++];

    /* Does the probe data contain the whole header? */
    if (p->buf_size < 4 + size + total)
        return 0;

    /* The header should contain a known document type. For now,
     * we don't parse the whole header but simply check for the
     * availability of that array of characters inside the header.
     * Not fully fool-proof, but good enough. */
    for (i = 0; i < FF_ARRAY_ELEMS(matroska_doctypes); i++) {
        size_t probelen = strlen(matroska_doctypes[i]);
        if (total < probelen)
            continue;
        for (n = 4 + size; n <= 4 + size + total - probelen; n++)
            if (!memcmp(p->buf + n, matroska_doctypes[i], probelen))
                return AVPROBE_SCORE_MAX;
    }

    // probably valid EBML header but no recognized doctype
    return AVPROBE_SCORE_EXTENSION;
}

ASF/WMV文件的特征码就是ASF_HEADER_GUID，下面是FFmpeg中asf探测函数：

//libavformat/asfdec_f.c
const ff_asf_guid ff_asf_header = {
    0x30, 0x26, 0xB2, 0x75, 0x8E, 0x66, 0xCF, 0x11, 0xA6, 0xD9, 0x00, 0xAA, 0x00, 0x62, 0xCE, 0x6C
};
static int asf_probe(AVProbeData *pd)
{
    /* check file header */
    if (!ff_guidcmp(pd->buf, &ff_asf_header))
        return AVPROBE_SCORE_MAX;
    else
        return 0;
}

MP4文件是由不同BOX构成的，需要根据box type来探测实际类型，FFmpeg中mp4探测函数（也包括mov,m4a,3gp,3g2）如下：

//libavformat/mov.c
static int mov_probe(AVProbeData *p)
{
    int64_t offset;
    uint32_t tag;
    int score = 0;
    int moov_offset = -1;

    /* check file header */
    offset = 0;
    for (;;) {
        /* ignore invalid offset */
        if ((offset + 8) > (unsigned int)p->buf_size)
            break;
        tag = AV_RL32(p->buf + offset + 4);
        switch(tag) {
        /* check for obvious tags */
        case MKTAG('m','o','o','v'):
            moov_offset = offset + 4;
        case MKTAG('m','d','a','t'):
        case MKTAG('p','n','o','t'): /* detect movs with preview pics like ew.mov and april.mov */
        case MKTAG('u','d','t','a'): /* Packet Video PVAuthor adds this and a lot of more junk */
        case MKTAG('f','t','y','p'):
            if (AV_RB32(p->buf+offset) < 8 &&
                (AV_RB32(p->buf+offset) != 1 ||
                 offset + 12 > (unsigned int)p->buf_size ||
                 AV_RB64(p->buf+offset + 8) == 0)) {
                score = FFMAX(score, AVPROBE_SCORE_EXTENSION);
            } else if (tag == MKTAG('f','t','y','p') &&
                       (   AV_RL32(p->buf + offset + 8) == MKTAG('j','p','2',' ')
                        || AV_RL32(p->buf + offset + 8) == MKTAG('j','p','x',' ')
                    )) {
                score = FFMAX(score, 5);
            } else {
                score = AVPROBE_SCORE_MAX;
            }
            offset = FFMAX(4, AV_RB32(p->buf+offset)) + offset;
            break;
        /* those are more common words, so rate then a bit less */
        case MKTAG('e','d','i','w'): /* xdcam files have reverted first tags */
        case MKTAG('w','i','d','e'):
        case MKTAG('f','r','e','e'):
        case MKTAG('j','u','n','k'):
        case MKTAG('p','i','c','t'):
            score  = FFMAX(score, AVPROBE_SCORE_MAX - 5);
            offset = FFMAX(4, AV_RB32(p->buf+offset)) + offset;
            break;
        case MKTAG(0x82,0x82,0x7f,0x7d):
        case MKTAG('s','k','i','p'):
        case MKTAG('u','u','i','d'):
        case MKTAG('p','r','f','l'):
            /* if we only find those cause probedata is too small at least rate them */
            score  = FFMAX(score, AVPROBE_SCORE_EXTENSION);
            offset = FFMAX(4, AV_RB32(p->buf+offset)) + offset;
            break;
        default:
            offset = FFMAX(4, AV_RB32(p->buf+offset)) + offset;
        }
    }
    if(score > AVPROBE_SCORE_MAX - 50 && moov_offset != -1) {
        /* moov atom in the header - we should make sure that this is not a
         * MOV-packed MPEG-PS */
        offset = moov_offset;

        while(offset < (p->buf_size - 16)){ /* Sufficient space */
               /* We found an actual hdlr atom */
            if(AV_RL32(p->buf + offset     ) == MKTAG('h','d','l','r') &&
               AV_RL32(p->buf + offset +  8) == MKTAG('m','h','l','r') &&
               AV_RL32(p->buf + offset + 12) == MKTAG('M','P','E','G')){
                av_log(NULL, AV_LOG_WARNING, "Found media data tag MPEG indicating this is a MOV-packed MPEG-PS.\n");
                /* We found a media handler reference atom describing an
                 * MPEG-PS-in-MOV, return a
                 * low score to force expanding the probe window until
                 * mpegps_probe finds what it needs */
                return 5;
            }else
                /* Keep looking */
                offset+=2;
        }
    }

    return score;
}

对于像TS这种流媒体格式，通常通过0x47同步字节和pid判断，FFmpeg中ts的探测函数如下：

//libavformat/mpegts.c
static int analyze(const uint8_t *buf, int size, int packet_size,
                   int probe)
{
    int stat[TS_MAX_PACKET_SIZE];
    int stat_all = 0;
    int i;
    int best_score = 0;

    memset(stat, 0, packet_size * sizeof(*stat));

    for (i = 0; i < size - 3; i++) {
        if (buf[i] == 0x47) {
            int pid = AV_RB16(buf+1) & 0x1FFF;
            int asc = buf[i + 3] & 0x30;
            if (!probe || pid == 0x1FFF || asc) {
                int x = i % packet_size;
                stat[x]++;
                stat_all++;
                if (stat[x] > best_score) {
                    best_score = stat[x];
                }
            }
        }
    }

    return best_score - FFMAX(stat_all - 10*best_score, 0)/10;
}
static int mpegts_probe(AVProbeData *p)
{
    const int size = p->buf_size;
    int maxscore = 0;
    int sumscore = 0;
    int i;
    int check_count = size / TS_FEC_PACKET_SIZE;
#define CHECK_COUNT 10
#define CHECK_BLOCK 100

    if (!check_count)
        return 0;

    for (i = 0; i<check_count; i+=CHECK_BLOCK) {
        int left = FFMIN(check_count - i, CHECK_BLOCK);
        int score      = analyze(p->buf + TS_PACKET_SIZE     *i, TS_PACKET_SIZE     *left, TS_PACKET_SIZE     , 1);
        int dvhs_score = analyze(p->buf + TS_DVHS_PACKET_SIZE*i, TS_DVHS_PACKET_SIZE*left, TS_DVHS_PACKET_SIZE, 1);
        int fec_score  = analyze(p->buf + TS_FEC_PACKET_SIZE *i, TS_FEC_PACKET_SIZE *left, TS_FEC_PACKET_SIZE , 1);
        score = FFMAX3(score, dvhs_score, fec_score);
        sumscore += score;
        maxscore = FFMAX(maxscore, score);
    }

    sumscore = sumscore * CHECK_COUNT / check_count;
    maxscore = maxscore * CHECK_COUNT / CHECK_BLOCK;

    ff_dlog(0, "TS score: %d %d\n", sumscore, maxscore);

    if        (check_count > CHECK_COUNT && sumscore > 6) {
        return AVPROBE_SCORE_MAX   + sumscore - CHECK_COUNT;
    } else if (check_count >= CHECK_COUNT && sumscore > 6) {
        return AVPROBE_SCORE_MAX/2 + sumscore - CHECK_COUNT;
    } else if (check_count >= CHECK_COUNT && maxscore > 6) {
        return AVPROBE_SCORE_MAX/2 + sumscore - CHECK_COUNT;
    } else if (sumscore > 6) {
        return 2;
    } else {
        return 0;
    }
}