diff --git a/libavcodec/bitstream_filter.c b/libavcodec/bitstream_filter.c
index ef2d7414a6..e4be773c6e 100644
--- a/libavcodec/bitstream_filter.c
+++ b/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;
         }
     }