store a identifer and the first header in extradata

with this mp3 should be binary identical to what you had before header compression
support mp3 with crc (by droping the crc and putting it back during header decompress, currently its just random tough, does any deocoder even check it?)

Originally committed as revision 6960 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavcodec/bitstream_filter.c

@@ -125,21 +125,24 @@ static int noise(AVBitStreamFilterContext *bsfc, AVCodecContext *avctx, const ch
     return 1;
 }
 
+#define MP3_MASK 0xFFFE0CCF
+
 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;
+    uint32_t header, extraheader;
+    int mode_extension, header_size;
 
     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];
+    header = BE_32(buf);
     mode_extension= (header>>4)&3;
 
-    if(ff_mpa_check_header(header) < 0 || (header&0x70000) != 0x30000){
+    if(ff_mpa_check_header(header) < 0 || (header&0x60000) != 0x20000){
+output_unchanged:
         *poutbuf= (uint8_t *) buf;
         *poutbuf_size= buf_size;
 
@@ -147,9 +150,25 @@ static int mp3_header_compress(AVBitStreamFilterContext *bsfc, AVCodecContext *a
         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->extradata_size == 0){
+        avctx->extradata_size=15;
+        avctx->extradata= av_malloc(avctx->extradata_size);
+        strcpy(avctx->extradata, "FFCMP3 0.0");
+        memcpy(avctx->extradata+11, buf, 4);
+    }
+    if(avctx->extradata_size != 15){
+        av_log(avctx, AV_LOG_ERROR, "Extradata invalid\n");
+        return -1;
+    }
+    extraheader = BE_32(avctx->extradata+11);
+    if((extraheader&MP3_MASK) != (header&MP3_MASK))
+        goto output_unchanged;
+
+    header_size= (header&0x10000) ? 4 : 6;
+
+    *poutbuf_size= buf_size - header_size;
+    *poutbuf= av_malloc(buf_size - header_size + FF_INPUT_BUFFER_PADDING_SIZE);
+    memcpy(*poutbuf, buf + header_size, buf_size - header_size + FF_INPUT_BUFFER_PADDING_SIZE);
 
     if(avctx->channels==2){
         if((header & (3<<19)) != 3<<19){
@@ -173,7 +192,7 @@ static int mp3_header_decompress(AVBitStreamFilterContext *bsfc, AVCodecContext
     int sample_rate_index=0;
     int lsf, mpeg25, bitrate_index, frame_size;
 
-    header = (buf[0] << 24) | (buf[1] << 16) | (buf[2] << 8) | buf[3];
+    header = BE_32(buf);
     if(ff_mpa_check_header(header) >= 0){
         *poutbuf= (uint8_t *) buf;
         *poutbuf_size= buf_size;
@@ -181,18 +200,16 @@ static int mp3_header_decompress(AVBitStreamFilterContext *bsfc, AVCodecContext
         return 0;
     }
 
-    header= 0xFFE00000 | ((4-3)<<17) | (1<<16); //FIXME simplify
+    if(avctx->extradata_size != 15 || strcmp(avctx->extradata, "FFCMP3 0.0")){
+        av_log(avctx, AV_LOG_ERROR, "Extradata invalid %d\n", avctx->extradata_size);
+        return -1;
+    }
+
+    header= BE_32(avctx->extradata+11) & MP3_MASK;
 
     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_index= (header>>10)&3;
     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++){
@@ -200,6 +217,8 @@ static int mp3_header_decompress(AVBitStreamFilterContext *bsfc, AVCodecContext
         frame_size = (frame_size * 144000) / (sample_rate << lsf) + (bitrate_index&1);
         if(frame_size == buf_size + 4)
             break;
+        if(frame_size == buf_size + 6)
+            break;
     }
     if(bitrate_index == 30){
         av_log(avctx, AV_LOG_ERROR, "couldnt find bitrate_index\n");
@@ -208,18 +227,19 @@ static int mp3_header_decompress(AVBitStreamFilterContext *bsfc, AVCodecContext
 
     header |= (bitrate_index&1)<<9;
     header |= (bitrate_index>>1)<<12;
-    header |= (avctx->channels==1 ? MPA_MONO : MPA_JSTEREO)<<6;
+    header |= (frame_size == buf_size + 4)<<16; //FIXME actually set a correct crc instead of 0
 
-    *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);
+    *poutbuf_size= frame_size;
+    *poutbuf= av_malloc(frame_size + FF_INPUT_BUFFER_PADDING_SIZE);
+    memcpy(*poutbuf + frame_size - buf_size, buf, buf_size + FF_INPUT_BUFFER_PADDING_SIZE);
 
     if(avctx->channels==2){
+        uint8_t *p= *poutbuf + frame_size - buf_size;
         if(lsf){
-            FFSWAP(int, (*poutbuf)[5], (*poutbuf)[6]);
-            header |= ((*poutbuf)[5] & 0xC0)>>2;
+            FFSWAP(int, p[1], p[2]);
+            header |= (p[1] & 0xC0)>>2;
         }else{
-            header |= (*poutbuf)[5] & 0x30;
+            header |= p[1] & 0x30;
         }
     }