ac3_parser.h File Reference

#include "ac3.h"
#include "bitstream.h"

Go to the source code of this file.

Enumerations
enum	AC3ParseError {   AC3_PARSE_ERROR_SYNC = -1, AC3_PARSE_ERROR_BSID = -2, AC3_PARSE_ERROR_SAMPLE_RATE = -3, AC3_PARSE_ERROR_FRAME_SIZE = -4,   AC3_PARSE_ERROR_FRAME_TYPE = -5, AC3_PARSE_ERROR_CRC = -6 }
Functions
int	ff_ac3_parse_header (GetBitContext *gbc, AC3HeaderInfo *hdr)
int	ff_ac3_parse_header_full (GetBitContext *gbc, AC3HeaderInfo *hdr)

---

Enumeration Type Documentation

enum AC3ParseError

Enumerator:

AC3_PARSE_ERROR_SYNC
AC3_PARSE_ERROR_BSID
AC3_PARSE_ERROR_SAMPLE_RATE
AC3_PARSE_ERROR_FRAME_SIZE
AC3_PARSE_ERROR_FRAME_TYPE
AC3_PARSE_ERROR_CRC

Definition at line 29 of file ac3_parser.h.

             {
    AC3_PARSE_ERROR_SYNC        = -1,
    AC3_PARSE_ERROR_BSID        = -2,
    AC3_PARSE_ERROR_SAMPLE_RATE = -3,
    AC3_PARSE_ERROR_FRAME_SIZE  = -4,
    AC3_PARSE_ERROR_FRAME_TYPE  = -5,
    AC3_PARSE_ERROR_CRC         = -6,
} AC3ParseError;

---

Function Documentation

int ff_ac3_parse_header	(	GetBitContext *	gbc,
		AC3HeaderInfo *	hdr
	)

Parses AC-3 frame header. Parses the header up to the lfeon element, which is the first 52 or 54 bits depending on the audio coding mode.

Parameters:

	gbc[in]	BitContext containing the first 54 bits of the frame.
	hdr[out]	Pointer to struct where header info is written.

Returns:

Returns 0 on success, -1 if there is a sync word mismatch, -2 if the bsid (version) element is invalid, -3 if the fscod (sample rate) element is invalid, or -4 if the frmsizecod (bit rate) element is invalid.

Definition at line 37 of file ac3_parser.c.

References AC3_CHMODE_MONO, AC3_CHMODE_STEREO, AC3_HEADER_SIZE, AC3_PARSE_ERROR_BSID, AC3_PARSE_ERROR_FRAME_SIZE, AC3_PARSE_ERROR_FRAME_TYPE, AC3_PARSE_ERROR_SAMPLE_RATE, AC3_PARSE_ERROR_SYNC, eac3_blocks, EAC3_FRAME_TYPE_AC3_CONVERT, EAC3_FRAME_TYPE_RESERVED, ff_ac3_bitrate_tab, ff_ac3_channels_tab, ff_ac3_frame_size_tab, ff_ac3_sample_rate_tab, FFMAX, get_bits(), get_bits1(), show_bits_long(), and skip_bits().

Referenced by ac3_probe(), ac3_sync(), ff_ac3_parse_header_full(), and parse_frame_header().

{
    int frame_size_code;

    memset(hdr, 0, sizeof(*hdr));

    hdr->sync_word = get_bits(gbc, 16);
    if(hdr->sync_word != 0x0B77)
        return AC3_PARSE_ERROR_SYNC;

    /* read ahead to bsid to distinguish between AC-3 and E-AC-3 */
    hdr->bitstream_id = show_bits_long(gbc, 29) & 0x1F;
    if(hdr->bitstream_id > 16)
        return AC3_PARSE_ERROR_BSID;

    hdr->num_blocks = 6;

    /* set default mix levels */
    hdr->center_mix_level   = 1;  // -4.5dB
    hdr->surround_mix_level = 1;  // -6.0dB

    if(hdr->bitstream_id <= 10) {
        /* Normal AC-3 */
        hdr->crc1 = get_bits(gbc, 16);
        hdr->sr_code = get_bits(gbc, 2);
        if(hdr->sr_code == 3)
            return AC3_PARSE_ERROR_SAMPLE_RATE;

        frame_size_code = get_bits(gbc, 6);
        if(frame_size_code > 37)
            return AC3_PARSE_ERROR_FRAME_SIZE;

        skip_bits(gbc, 5); // skip bsid, already got it

        skip_bits(gbc, 3); // skip bitstream mode
        hdr->channel_mode = get_bits(gbc, 3);

        if(hdr->channel_mode == AC3_CHMODE_STEREO) {
            skip_bits(gbc, 2); // skip dsurmod
        } else {
            if((hdr->channel_mode & 1) && hdr->channel_mode != AC3_CHMODE_MONO)
                hdr->center_mix_level = get_bits(gbc, 2);
            if(hdr->channel_mode & 4)
                hdr->surround_mix_level = get_bits(gbc, 2);
        }
        hdr->lfe_on = get_bits1(gbc);

        hdr->sr_shift = FFMAX(hdr->bitstream_id, 8) - 8;
        hdr->sample_rate = ff_ac3_sample_rate_tab[hdr->sr_code] >> hdr->sr_shift;
        hdr->bit_rate = (ff_ac3_bitrate_tab[frame_size_code>>1] * 1000) >> hdr->sr_shift;
        hdr->channels = ff_ac3_channels_tab[hdr->channel_mode] + hdr->lfe_on;
        hdr->frame_size = ff_ac3_frame_size_tab[frame_size_code][hdr->sr_code] * 2;
        hdr->frame_type = EAC3_FRAME_TYPE_AC3_CONVERT; //EAC3_FRAME_TYPE_INDEPENDENT;
        hdr->substreamid = 0;
    } else {
        /* Enhanced AC-3 */
        hdr->crc1 = 0;
        hdr->frame_type = get_bits(gbc, 2);
        if(hdr->frame_type == EAC3_FRAME_TYPE_RESERVED)
            return AC3_PARSE_ERROR_FRAME_TYPE;

        hdr->substreamid = get_bits(gbc, 3);

        hdr->frame_size = (get_bits(gbc, 11) + 1) << 1;
        if(hdr->frame_size < AC3_HEADER_SIZE)
            return AC3_PARSE_ERROR_FRAME_SIZE;

        hdr->sr_code = get_bits(gbc, 2);
        if (hdr->sr_code == 3) {
            int sr_code2 = get_bits(gbc, 2);
            if(sr_code2 == 3)
                return AC3_PARSE_ERROR_SAMPLE_RATE;
            hdr->sample_rate = ff_ac3_sample_rate_tab[sr_code2] / 2;
            hdr->sr_shift = 1;
        } else {
            hdr->num_blocks = eac3_blocks[get_bits(gbc, 2)];
            hdr->sample_rate = ff_ac3_sample_rate_tab[hdr->sr_code];
            hdr->sr_shift = 0;
        }

        hdr->channel_mode = get_bits(gbc, 3);
        hdr->lfe_on = get_bits1(gbc);

        hdr->bit_rate = (uint32_t)(8.0 * hdr->frame_size * hdr->sample_rate /
                        (hdr->num_blocks * 256.0));
        hdr->channels = ff_ac3_channels_tab[hdr->channel_mode] + hdr->lfe_on;
    }

    return 0;
}

int ff_ac3_parse_header_full	(	GetBitContext *	gbc,
		AC3HeaderInfo *	hdr
	)

Parses AC-3 frame header and sets channel_map Parses the header up to the lfeon (channel_map in E-AC-3) element, which is the first 52, 54 or 104 bits depending on the audio coding mode.

Parameters:

	gbc[in]	BitContext containing the first 54 bits of the frame.
	hdr[out]	Pointer to struct where header info is written.

Returns:

value returned by ff_ac3_parse_header

Definition at line 128 of file ac3_parser.c.

References AC3_CHMAP_LFE, AC3HeaderInfo::bitstream_id, AC3HeaderInfo::channel_map, AC3HeaderInfo::channel_mode, EAC3_FRAME_TYPE_DEPENDENT, ff_ac3_parse_header(), ff_eac3_default_chmap, AC3HeaderInfo::frame_type, get_bits(), get_bits1(), AC3HeaderInfo::lfe_on, and skip_bits().

                                                                    {
    int ret, i;
    ret = ff_ac3_parse_header(gbc, hdr);
    if(!ret){
        if(hdr->bitstream_id>10){
            /* Enhanced AC-3 */
            skip_bits(gbc, 5); // skip bitstream id

            /* skip dialog normalization and compression gain */
            for (i = 0; i < (hdr->channel_mode ? 1 : 2); i++) {
                skip_bits(gbc, 5); // skip dialog normalization
                if (get_bits1(gbc)) {
                    skip_bits(gbc, 8); //skip Compression gain word
                }
            }
            /* dependent stream channel map */
            if (hdr->frame_type == EAC3_FRAME_TYPE_DEPENDENT && get_bits1(gbc)) {
                    hdr->channel_map = get_bits(gbc, 16); //custom channel map
                    return 0;
            }
        }
        //default channel map based on acmod and lfeon
        hdr->channel_map = ff_eac3_default_chmap[hdr->channel_mode];
        if(hdr->lfe_on)
            hdr->channel_map |= AC3_CHMAP_LFE;
    }
    return ret;
}

---