Fix decoding of:

http://samples.mplayerhq.hu/A-codecs/msgsm/levis.avi
http://samples.mplayerhq.hu/A-codecs/msgsm/wernfried_1.avi

partially fix decoding of:
http://samples.mplayerhq.hu/A-codecs/GSM/sample-gsm-8000.gsm

Allow the user to encode non standard samplerates by using -strict

Originally committed as revision 13020 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavcodec/libgsm.c

@@ -41,9 +41,18 @@ static av_cold int libgsm_init(AVCodecContext *avctx) {
                avctx->channels);
         return -1;
     }
+
+    if(avctx->codec->decode){
+        if(!avctx->channels)
+            avctx->channels= 1;
+
+        if(!avctx->sample_rate)
+            avctx->sample_rate= 8000;
+    }else{
     if (avctx->sample_rate != 8000) {
         av_log(avctx, AV_LOG_ERROR, "Sample rate 8000Hz required for GSM, got %dHz\n",
                avctx->sample_rate);
+        if(avctx->strict_std_compliance > FF_COMPLIANCE_INOFFICIAL)
         return -1;
     }
     if (avctx->bit_rate != 13000 /* Official */ &&
@@ -51,8 +60,10 @@ static av_cold int libgsm_init(AVCodecContext *avctx) {
         avctx->bit_rate != 0 /* Unknown; a.o. mov does not set bitrate when decoding */ ) {
         av_log(avctx, AV_LOG_ERROR, "Bitrate 13000bps required for GSM, got %dbps\n",
                avctx->bit_rate);
+        if(avctx->strict_std_compliance > FF_COMPLIANCE_INOFFICIAL)
         return -1;
     }
+    }
 
     avctx->priv_data = gsm_create();