lpcmstrm_in.cpp

来自「Motion JPEG编解码器源代码」· C++ 代码 · 共 324 行

/*
 *  lpcmstrm_in.c: LPCM Audio strem class members handling scanning and
 *  buffering raw input stream.
 *
 * Takes a *RAW* LPCM stream as input.
 * This is *signed* linear 16, 20, or 24-bit sample PCM.
 * Samples are stored msb first.
 * How  20-bit samples are allocated to bytes? I just don't know, but
 * believe 4 bits are appended after the lsb (samples are msb-byte aligned).
 *
 *  Copyright (C) 2001 Andrew Stevens <[e-mail]>
 *  Copyright (C) 2000,2001 Brent Byeler for original header-structure
 *                          parsing code.
 *
 *
 *  This program is free software; you can redistribute it and/or
 *  modify it under the terms of version 2 of the GNU General Public License
 *  as published by the Free Software Foundation.
 *
 *  This program is distributed in the hope that it will be useful,
 *  but WITHOUT ANY WARRANTY; without even the implied warranty of
 *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 *  GNU General Public License for more details.
 *
 *  You should have received a copy of the GNU General Public License
 *  along with this program; if not, write to the Free Software
 *  Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA  02111-1307, USA.
 */

#include <config.h>
#include <math.h>
#include <stdlib.h>
#include <string.h>

#include "audiostrm.hpp"
#include "interact.hpp"
#include "multiplexor.hpp"


const unsigned int LPCMStream::default_buffer_size = 58*1024;
const unsigned int LPCMStream::ticks_per_frame_90kHz = 150;


LPCMStream::LPCMStream(IBitStream &ibs, LpcmParams *parms, Multiplexor &into) : 
	AudioStream( ibs, into ),
    parms(parms)
{
	num_frames = 0;
}




bool LPCMStream::Probe(IBitStream &bs )
{
    char *last_dot = strrchr( bs.StreamName(), '.' );
    return 
        last_dot != NULL 
        && strcmp( last_dot+1, "lpcm") == 0;

}


/*************************************************************************
 *
 * Reads initial stream parameters and displays feedback banner to users
 *
 *************************************************************************/


void LPCMStream::Init ( const int _stream_num)

{
    stream_num = _stream_num;
    header_skip = 0;
	MuxStream::Init( PRIVATE_STR_1, 
					 1,  // Buffer scale
					 default_buffer_size,
					 false,
					 muxinto.buffers_in_audio,
					 muxinto.always_buffers_in_audio
		);

    // This seems to be necessary not only for some software players but
    // for some standalone players too.   Yuck... shades of the VCD audio
    // sectors.
    min_pes_header_len = 10;
    mjpeg_info ("Scanning for header info: LPCM Audio stream %02x (%s)",
                stream_num,
                bs.StreamName()
                );

    
	AU_start = bs.bitcount();

    // This is a dummy debug version that simply assumes 48kHz
    // two channel 16 bit sample LPCM
    
    samples_per_second = parms->SamplesPerSec();
    channels = parms->Channels();
    bits_per_sample = parms->BitsPerSample();
    bytes_per_frame = 
        samples_per_second * channels * bits_per_sample / 8
        * ticks_per_frame_90kHz
        / 90000;
    frame_index = 0;
    dynamic_range_code = 0x80;

    /* Presentation/decoding time-stamping  */
    access_unit.start = AU_start;
    access_unit.length = bytes_per_frame;
    access_unit.PTS = static_cast<clockticks>(decoding_order) * 
        (CLOCKS_per_90Kth_sec * ticks_per_frame_90kHz);
    access_unit.DTS = access_unit.PTS;
    access_unit.dorder = decoding_order;
    decoding_order++;
    aunits.Append( access_unit );
    
	OutputHdrInfo();
}

unsigned int LPCMStream::NominalBitRate()
{ 
	return samples_per_second * channels * bits_per_sample;
}



void LPCMStream::FillAUbuffer(unsigned int frames_to_buffer )
{
	last_buffered_AU += frames_to_buffer;
	mjpeg_debug( "Scanning %d MPEG LPCM audio frames to frame %d", 
				 frames_to_buffer, last_buffered_AU );

	while ( !bs.eos() 
            && decoding_order < last_buffered_AU 
            && !muxinto.AfterMaxPTS(access_unit.PTS) )
	{
		int skip=access_unit.length; 
        bs.SeekFwdBits( skip );
		prev_offset = AU_start;
		AU_start = bs.bitcount();
        if( AU_start - prev_offset != access_unit.length*8 )
        {
            mjpeg_warn("Discarding incomplete final frame LPCM  stream %d",
                       stream_num);
            aunits.DropLast();
            --decoding_order;
            break;
        }

        // Here we would check for header data but LPCM has no headers...
        if( bs.eos()   )
            break;

		access_unit.start = AU_start;
		access_unit.length = bytes_per_frame;
		access_unit.PTS = static_cast<clockticks>(decoding_order) * 
            (CLOCKS_per_90Kth_sec * ticks_per_frame_90kHz);
		access_unit.DTS = access_unit.PTS;
		access_unit.dorder = decoding_order;
		decoding_order++;
		aunits.Append( access_unit );
		num_frames++;
		
		num_syncword++;

		if (num_syncword >= old_frames+10 )
		{
			mjpeg_debug ("Got %d frame headers.", num_syncword);
			old_frames=num_syncword;
		}
        mjpeg_debug( "Got frame %d\n", decoding_order );

    }
	last_buffered_AU = decoding_order;
	eoscan =  bs.eos() || muxinto.AfterMaxPTS(access_unit.PTS);
}



void LPCMStream::Close()
{
    stream_length = AU_start / 8;
	mjpeg_info ("AUDIO_STATISTICS: %02x", stream_id); 
    mjpeg_info ("Audio stream length %lld bytes.", stream_length);
    mjpeg_info   ("Frames         : %8u ",  num_frames);
}

/*************************************************************************
	OutputAudioInfo
	gibt gesammelte Informationen zu den Audio Access Units aus.

	Prints information on audio access units
*************************************************************************/

void LPCMStream::OutputHdrInfo ()
{
	mjpeg_info("LPCM AUDIO STREAM:");

    mjpeg_info ("Bit rate       : %8u bytes/sec (%u) bit/sec)",
                NominalBitRate()/8, NominalBitRate() );
    mjpeg_info ("Channels       :     %d", channels);
    mjpeg_info ("Bits per sample:     %d", bits_per_sample );
    mjpeg_info ("Frequency      :     %d Hz", samples_per_second );

}


unsigned int 
LPCMStream::ReadPacketPayload(uint8_t *dst, unsigned int to_read)
{
    unsigned int header_size = LPCMStream::StreamHeaderSize();
    bitcount_t read_start = bs.GetBytePos();
    unsigned int bytes_read = bs.GetBytes( dst+header_size, 
                                           to_read-header_size );
    bs.Flush( read_start );
    
	clockticks   decode_time;
    bool starting_frame_found = false;
    uint8_t starting_frame_index = 0;

    int starting_frame_offset = 
        (new_au_next_sec || au_unsent > bytes_read )
        ? 0 
        : au_unsent;

    unsigned int frames = 0;
    unsigned int bytes_muxed = bytes_read;
  
	if (bytes_muxed == 0 || MuxCompleted() )
    {
		goto completion;
    }


	/* Work through what's left of the current frames and the
	   following frames's updating the info until we reach a point where
	   an frame had to be split between packets. 

	   The DTS/PTS field for the packet in this case would have been
	   given the that for the first AU to start in the packet.

	*/

	decode_time = RequiredDTS();
	while (au_unsent < bytes_muxed)
	{	  
        assert( bytes_muxed > 1 );
		bufmodel.Queued(au_unsent, decode_time);
		bytes_muxed -= au_unsent;
        if( new_au_next_sec )
        {
            ++frames;
            if( ! starting_frame_found )
            {
                starting_frame_index = static_cast<uint8_t>(au->dorder % 20);
                starting_frame_found = true;
            }
        }
		if( !NextAU() )
        {
            goto completion;
        }
		new_au_next_sec = true;
		decode_time = RequiredDTS();
	};

	// We've now reached a point where the current AU overran or
	// fitted exactly.  We need to distinguish the latter case so we
	// can record whether the next packet starts with the tail end of
	// // an already started frame or a new one. We need this info to
	// decide what PTS/DTS info to write at the start of the next
	// packet.
	
	if (au_unsent > bytes_muxed)
	{
        if( new_au_next_sec )
            ++frames;
		bufmodel.Queued( bytes_muxed, decode_time);
		au_unsent -= bytes_muxed;
		new_au_next_sec = false;
	} 
	else //  if (au_unsent == bytes_muxed)
	{
		bufmodel.Queued(bytes_muxed, decode_time);
        if( new_au_next_sec )
            ++frames;
        new_au_next_sec = NextAU();
	}	   
completion:
    // Generate the LPCM header...
    // Note the index counts from the low byte of the offset so
    // the smallest value is 1!
    dst[0] = LPCM_SUB_STR_0 + stream_num;
    dst[1] = frames;
    dst[2] = (starting_frame_offset+1)>>8;
    dst[3] = (starting_frame_offset+1)&0xff;
    unsigned int bps_code;
    switch( bits_per_sample )
    {
    case 16 : bps_code = 0; break;
    case 20 : bps_code = 1; break;
    case 24 : bps_code = 2; break;
    default : bps_code = 3; break;
    }
    dst[4] = starting_frame_index;
    unsigned int bsf_code = (samples_per_second == 48000) ? 0 : 1;
    unsigned int channels_code = channels - 1;
    dst[5] = (bps_code << 6) | (bsf_code << 4) | channels_code;
    dst[6] = dynamic_range_code;
	return bytes_read+header_size;
}



/* 
 * Local variables:
 *  c-file-style: "stroustrup"
 *  tab-width: 4
 *  indent-tabs-mode: nil
 * End:
 */