av_log(s, AV_LOG_ERROR, "Cannot handle luma only YUV4MPEG stream.\n"); return -1;
pix_fmt = PIX_FMT_GRAY8;
static int yuv4_read_header(AVFormatContext *s, AVFormatParameters *ap){    char header[MAX_YUV4_HEADER+10];  // Include headroom for the longest option    char *tokstart,*tokend,*header_end;    int i;    ByteIOContext *pb = &s->pb;    int width=-1, height=-1, raten=0, rated=0, aspectn=0, aspectd=0,interlaced_frame=0,top_field_first=0;    enum PixelFormat pix_fmt=PIX_FMT_NB,alt_pix_fmt=PIX_FMT_NB;    AVStream *st;        for (i=0; i<MAX_YUV4_HEADER; i++) {        header[i] = get_byte(pb);	if (header[i] == '\n') {	    header[i+1] = 0x20;  // Add a space after last option. Makes parsing "444" vs "444alpha" easier.	    header[i+2] = 0;	    break;	}    }    if (i == MAX_YUV4_HEADER) return -1;    if (strncmp(header, Y4M_MAGIC, strlen(Y4M_MAGIC))) return -1;    header_end = &header[i+1]; // Include space    for(tokstart = &header[strlen(Y4M_MAGIC) + 1]; tokstart < header_end; tokstart++) {        if (*tokstart==0x20) continue;        switch (*tokstart++) {        case 'W': // Width. Required.            width = strtol(tokstart, &tokend, 10);            tokstart=tokend;            break;        case 'H': // Height. Required.            height = strtol(tokstart, &tokend, 10);            tokstart=tokend;            break;        case 'C': // Color space            if (strncmp("420jpeg",tokstart,7)==0)                pix_fmt = PIX_FMT_YUV420P;            else if (strncmp("420mpeg2",tokstart,8)==0)                pix_fmt = PIX_FMT_YUV420P;            else if (strncmp("420paldv", tokstart, 8)==0)                pix_fmt = PIX_FMT_YUV420P;            else if (strncmp("411", tokstart, 3)==0)                pix_fmt = PIX_FMT_YUV411P;            else if (strncmp("422", tokstart, 3)==0)                pix_fmt = PIX_FMT_YUV422P;            else if (strncmp("444alpha", tokstart, 8)==0) {                av_log(s, AV_LOG_ERROR, "Cannot handle 4:4:4:4 YUV4MPEG stream.\n");                return -1;            } else if (strncmp("444", tokstart, 3)==0)                pix_fmt = PIX_FMT_YUV444P;            else if (strncmp("mono",tokstart, 4)==0) {                av_log(s, AV_LOG_ERROR, "Cannot handle luma only YUV4MPEG stream.\n");                return -1;            } else {                av_log(s, AV_LOG_ERROR, "YUV4MPEG stream contains an unknown pixel format.\n");                return -1;            }            while(tokstart<header_end&&*tokstart!=0x20) tokstart++;            break;        case 'I': // Interlace type            switch (*tokstart++){            case '?':                break;            case 'p':                interlaced_frame=0;                break;            case 't':                interlaced_frame=1;                top_field_first=1;                break;            case 'b':                interlaced_frame=1;                top_field_first=0;                break;            case 'm':                av_log(s, AV_LOG_ERROR, "YUV4MPEG stream contains mixed interlaced and non-interlaced frames.\n");                return -1;            default:                av_log(s, AV_LOG_ERROR, "YUV4MPEG has invalid header.\n");                return -1;            }            break;        case 'F': // Frame rate            sscanf(tokstart,"%d:%d",&raten,&rated); // 0:0 if unknown            while(tokstart<header_end&&*tokstart!=0x20) tokstart++;            break;        case 'A': // Pixel aspect            sscanf(tokstart,"%d:%d",&aspectn,&aspectd); // 0:0 if unknown            while(tokstart<header_end&&*tokstart!=0x20) tokstart++;            break;        case 'X': // Vendor extensions            if (strncmp("YSCSS=",tokstart,6)==0) {                // Older nonstandard pixel format representation                tokstart+=6;                if (strncmp("420JPEG",tokstart,7)==0)                    alt_pix_fmt=PIX_FMT_YUV420P;                else if (strncmp("420MPEG2",tokstart,8)==0)                    alt_pix_fmt=PIX_FMT_YUV420P;                else if (strncmp("420PALDV",tokstart,8)==0)                    alt_pix_fmt=PIX_FMT_YUV420P;                else if (strncmp("411",tokstart,3)==0)                    alt_pix_fmt=PIX_FMT_YUV411P;                else if (strncmp("422",tokstart,3)==0)                    alt_pix_fmt=PIX_FMT_YUV422P;                else if (strncmp("444",tokstart,3)==0)                    alt_pix_fmt=PIX_FMT_YUV444P;            }            while(tokstart<header_end&&*tokstart!=0x20) tokstart++;            break;        }    }                if ((width == -1) || (height == -1)) {        av_log(s, AV_LOG_ERROR, "YUV4MPEG has invalid header.\n");        return -1;            }        if (pix_fmt == PIX_FMT_NB) {        if (alt_pix_fmt == PIX_FMT_NB)            pix_fmt = PIX_FMT_YUV420P;        else            pix_fmt = alt_pix_fmt;    }    if (raten == 0 && rated == 0) {        // Frame rate unknown        raten = 25;        rated = 1;    }    if (aspectn == 0 && aspectd == 0) {        // Pixel aspect unknown        aspectd = 1;    }            st = av_new_stream(s, 0);    st = s->streams[0];    st->codec.width = width;    st->codec.height = height;    av_reduce(&raten, &rated, raten, rated, (1UL<<31)-1);    st->codec.frame_rate = raten;    st->codec.frame_rate_base = rated;    st->codec.pix_fmt = pix_fmt;    st->codec.codec_type = CODEC_TYPE_VIDEO;    st->codec.codec_id = CODEC_ID_RAWVIDEO;    st->codec.sample_aspect_ratio= (AVRational){aspectn, aspectd};    return 0;}