Function mpeg1_encode_sequence_header

libavcodec/mpeg12enc.c:149–308

put sequence header if needed */

/* put sequence header if needed */
static void mpeg1_encode_sequence_header(MPEG12EncContext *mpeg12)
{
    MPVEncContext *const s = &mpeg12->mpeg.s;
    unsigned int vbv_buffer_size, fps, v;
    int constraint_parameter_flag;
    AVRational framerate = ff_mpeg12_frame_rate_tab[mpeg12->frame_rate_index];
    uint64_t time_code;
    int64_t best_aspect_error = INT64_MAX;
    AVRational aspect_ratio = s->c.avctx->sample_aspect_ratio;
    int aspect_ratio_info;

    put_bits_assume_flushed(&s->pb);

    if (!(s->c.cur_pic.ptr->f->flags & AV_FRAME_FLAG_KEY))
        return;

    if (aspect_ratio.num == 0 || aspect_ratio.den == 0)
        aspect_ratio = (AVRational){1,1};             // pixel aspect 1.1 (VGA)

    /* MPEG-1 header repeated every GOP */
    put_header(s, SEQ_START_CODE);

    put_sbits(&s->pb, 12, s->c.width  & 0xFFF);
    put_sbits(&s->pb, 12, s->c.height & 0xFFF);

    for (int i = 1; i < 15; i++) {
        int64_t error = aspect_ratio.num * (1LL<<32) / aspect_ratio.den;
        if (s->c.codec_id == AV_CODEC_ID_MPEG1VIDEO || i <= 1)
            error -= (1LL<<32) / ff_mpeg1_aspect[i];
        else
            error -= (1LL<<32)*ff_mpeg2_aspect[i].num * s->c.height / s->c.width / ff_mpeg2_aspect[i].den;

        error = FFABS(error);

        if (error - 2 <= best_aspect_error) {
            best_aspect_error = error;
            aspect_ratio_info = i;
        }
    }

    put_bits(&s->pb, 4, aspect_ratio_info);
    put_bits(&s->pb, 4, mpeg12->frame_rate_index);

    if (s->c.avctx->rc_max_rate) {
        v = (s->c.avctx->rc_max_rate + 399) / 400;
        if (v > 0x3ffff && s->c.codec_id == AV_CODEC_ID_MPEG1VIDEO)
            v = 0x3ffff;
    } else {
        v = 0x3FFFF;
    }

    if (s->c.avctx->rc_buffer_size)
        vbv_buffer_size = s->c.avctx->rc_buffer_size;
    else
        /* VBV calculation: Scaled so that a VCD has the proper
         * VBV size of 40 kilobytes */
        vbv_buffer_size = av_rescale_rnd(mpeg12->mpeg.bit_rate, 20, 1151929 / 2, AV_ROUND_ZERO) * 8 * 1024;
    vbv_buffer_size = (vbv_buffer_size + 16383) / 16384;