From eacb41b2e984dc191ecf1b4ad018bb794524ba09 Mon Sep 17 00:00:00 2001
From: Michael Niedermayer <michaelni@gmx.at>
Date: Fri, 10 Nov 2006 01:41:53 +0000
Subject: mp3 header (de)compression bitstream filter this will make mp3 frames
 4 bytes smaller, it will not give you binary identical mp3 files, but it will
 give you mp3 files which decode to binary identical output this will only
 work in containers providing at least packet size, sample_rate and number of
 channels bugreports about mp3 files for which this fails are welcome and this
 is experimental (dont expect compatibility and dont even expect to be able to
 decompress what you compressed, hell dont even expect this to work without
 editing the source a little)

Originally committed as revision 6958 to svn://svn.ffmpeg.org/ffmpeg/trunk
---
 libavcodec/bitstream_filter.c | 119 ++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 119 insertions(+)

(limited to 'libavcodec/bitstream_filter.c')

diff --git a/libavcodec/bitstream_filter.c b/libavcodec/bitstream_filter.c
index 8f878cd0da..ef2d7414a6 100644
--- a/libavcodec/bitstream_filter.c
+++ b/libavcodec/bitstream_filter.c
@@ -19,6 +19,7 @@
  */
 
 #include "avcodec.h"
+#include "mpegaudio.h"
 
 AVBitStreamFilter *first_bitstream_filter= NULL;
 
@@ -124,6 +125,112 @@ static int noise(AVBitStreamFilterContext *bsfc, AVCodecContext *avctx, const ch
     return 1;
 }
 
+static int mp3_header_compress(AVBitStreamFilterContext *bsfc, AVCodecContext *avctx, const char *args,
+                     uint8_t **poutbuf, int *poutbuf_size,
+                     const uint8_t *buf, int buf_size, int keyframe){
+    uint32_t header;
+    int mode_extension;
+
+    if(avctx->strict_std_compliance > FF_COMPLIANCE_EXPERIMENTAL){
+        av_log(avctx, AV_LOG_ERROR, "not standards compliant\n");
+        return -1;
+    }
+
+    header = (buf[0] << 24) | (buf[1] << 16) | (buf[2] << 8) | buf[3];
+    mode_extension= (header>>4)&3;
+
+    if(ff_mpa_check_header(header) < 0 || (header&0x70000) != 0x30000){
+        *poutbuf= (uint8_t *) buf;
+        *poutbuf_size= buf_size;
+
+        av_log(avctx, AV_LOG_INFO, "cannot compress %08X\n", header);
+        return 0;
+    }
+
+    *poutbuf_size= buf_size - 4;
+    *poutbuf= av_malloc(buf_size - 4 + FF_INPUT_BUFFER_PADDING_SIZE);
+    memcpy(*poutbuf, buf + 4, buf_size - 4 + FF_INPUT_BUFFER_PADDING_SIZE);
+
+    if(avctx->channels==2){
+        if((header & (3<<19)) != 3<<19){
+            (*poutbuf)[1] &= 0x3F;
+            (*poutbuf)[1] |= mode_extension<<6;
+            FFSWAP(int, (*poutbuf)[1], (*poutbuf)[2]);
+        }else{
+            (*poutbuf)[1] &= 0x8F;
+            (*poutbuf)[1] |= mode_extension<<4;
+        }
+    }
+
+    return 1;
+}
+
+static int mp3_header_decompress(AVBitStreamFilterContext *bsfc, AVCodecContext *avctx, const char *args,
+                     uint8_t **poutbuf, int *poutbuf_size,
+                     const uint8_t *buf, int buf_size, int keyframe){
+    uint32_t header;
+    int sample_rate= avctx->sample_rate;
+    int sample_rate_index=0;
+    int lsf, mpeg25, bitrate_index, frame_size;
+
+    header = (buf[0] << 24) | (buf[1] << 16) | (buf[2] << 8) | buf[3];
+    if(ff_mpa_check_header(header) >= 0){
+        *poutbuf= (uint8_t *) buf;
+        *poutbuf_size= buf_size;
+
+        return 0;
+    }
+
+    header= 0xFFE00000 | ((4-3)<<17) | (1<<16); //FIXME simplify
+
+    lsf     = sample_rate < (24000+32000)/2;
+    mpeg25  = sample_rate < (12000+16000)/2;
+    header |= (!mpeg25)<<20;
+    header |= (!lsf   )<<19;
+    if(sample_rate<<(lsf+mpeg25) < (44100+32000)/2)
+        sample_rate_index |= 2;
+    else if(sample_rate<<(lsf+mpeg25) > (44100+48000)/2)
+        sample_rate_index |= 1;
+
+    header |= sample_rate_index<<10;
+    sample_rate= mpa_freq_tab[sample_rate_index] >> (lsf + mpeg25); //in case sample rate is a little off
+
+    for(bitrate_index=2; bitrate_index<30; bitrate_index++){
+        frame_size = mpa_bitrate_tab[lsf][2][bitrate_index>>1];
+        frame_size = (frame_size * 144000) / (sample_rate << lsf) + (bitrate_index&1);
+        if(frame_size == buf_size + 4)
+            break;
+    }
+    if(bitrate_index == 30){
+        av_log(avctx, AV_LOG_ERROR, "couldnt find bitrate_index\n");
+        return -1;
+    }
+
+    header |= (bitrate_index&1)<<9;
+    header |= (bitrate_index>>1)<<12;
+    header |= (avctx->channels==1 ? MPA_MONO : MPA_JSTEREO)<<6;
+
+    *poutbuf_size= buf_size + 4;
+    *poutbuf= av_malloc(buf_size + 4 + FF_INPUT_BUFFER_PADDING_SIZE);
+    memcpy(*poutbuf + 4, buf, buf_size + FF_INPUT_BUFFER_PADDING_SIZE);
+
+    if(avctx->channels==2){
+        if(lsf){
+            FFSWAP(int, (*poutbuf)[5], (*poutbuf)[6]);
+            header |= ((*poutbuf)[5] & 0xC0)>>2;
+        }else{
+            header |= (*poutbuf)[5] & 0x30;
+        }
+    }
+
+    (*poutbuf)[0]= header>>24;
+    (*poutbuf)[1]= header>>16;
+    (*poutbuf)[2]= header>> 8;
+    (*poutbuf)[3]= header    ;
+
+    return 1;
+}
+
 AVBitStreamFilter dump_extradata_bsf={
     "dump_extra",
     0,
@@ -141,3 +248,15 @@ AVBitStreamFilter noise_bsf={
     sizeof(int),
     noise,
 };
+
+AVBitStreamFilter mp3_header_compress_bsf={
+    "mp3comp",
+    0,
+    mp3_header_compress,
+};
+
+AVBitStreamFilter mp3_header_decompress_bsf={
+    "mp3decomp",
+    0,
+    mp3_header_decompress,
+};
-- 
cgit v1.2.3