if(buf_size < avpicture_get_size(avctx->pix_fmt, avctx->width, avctx->height) + 200){ av_log(avctx, AV_LOG_ERROR, "encoded frame too large\n"); return -1; }
static int pnm_encode_frame(AVCodecContext *avctx, unsigned char *outbuf, int buf_size, void *data){    PNMContext *s = avctx->priv_data;    AVFrame *pict = data;    AVFrame * const p= (AVFrame*)&s->picture;    int i, h, h1, c, n, linesize;    uint8_t *ptr, *ptr1, *ptr2;    *p = *pict;    p->pict_type= FF_I_TYPE;    p->key_frame= 1;        s->bytestream_start=    s->bytestream= outbuf;    s->bytestream_end= outbuf+buf_size;    h = avctx->height;    h1 = h;    switch(avctx->pix_fmt) {    case PIX_FMT_MONOWHITE:        c = '4';        n = (avctx->width + 7) >> 3;        break;    case PIX_FMT_GRAY8:        c = '5';        n = avctx->width;        break;    case PIX_FMT_RGB24:        c = '6';        n = avctx->width * 3;        break;    case PIX_FMT_YUV420P:        c = '5';        n = avctx->width;        h1 = (h * 3) / 2;        break;    default:        return -1;    }    snprintf(s->bytestream, s->bytestream_end - s->bytestream,              "P%c\n%d %d\n",             c, avctx->width, h1);    s->bytestream += strlen(s->bytestream);    if (avctx->pix_fmt != PIX_FMT_MONOWHITE) {        snprintf(s->bytestream, s->bytestream_end - s->bytestream,                  "%d\n", 255);        s->bytestream += strlen(s->bytestream);    }    ptr = p->data[0];    linesize = p->linesize[0];    for(i=0;i<h;i++) {        memcpy(s->bytestream, ptr, n);        s->bytestream += n;        ptr += linesize;    }        if (avctx->pix_fmt == PIX_FMT_YUV420P) {        h >>= 1;        n >>= 1;        ptr1 = p->data[1];        ptr2 = p->data[2];        for(i=0;i<h;i++) {            memcpy(s->bytestream, ptr1, n);            s->bytestream += n;            memcpy(s->bytestream, ptr2, n);            s->bytestream += n;                ptr1 += p->linesize[1];                ptr2 += p->linesize[2];        }    }    return s->bytestream - s->bytestream_start;}