ios - AVAssetWriter Writes Video but does not record AUDIO -

i have been successfull in making viedo (though blur) but have been unsuccessful in recording audio please help.

i using following code pls go through ans suggest solution or working tutorial.

i appending sample buffer using
[encoder._writerinput appendsamplebuffer:samplebuffer]; , app crashes when following statement called [encoder.audiowriterinput appendsamplebuffer:samplebuffer];

- (void) initpath:(nsstring*)path height:(int) height andwidth:(int) width bitrate:(int)bitrate {     self.path = path;     _bitrate = bitrate;      [[nsfilemanager defaultmanager] removeitematpath:self.path error:nil];     nsurl* url = [nsurl fileurlwithpath:self.path];      //initialize video writer     _writer = [avassetwriter assetwriterwithurl:url filetype:avfiletypempeg4 error:nil];      //initialize audio writer //    audiowriter = [avassetwriter assetwriterwithurl:url filetype:avfiletypecoreaudioformat error:nil];  //    nsdictionary* settings = @{ //        avvideocodeckey: avvideocodech264, //        avvideowidthkey: @(width), //        avvideoheightkey: @(height), //        avvideocompressionpropertieskey: @{ //             avvideoaveragebitratekey: @(self.bitrate), //             avvideomaxkeyframeintervalkey: @(150), //             avvideoprofilelevelkey: avvideoprofilelevelh264baselineautolevel, //             avvideoallowframereorderingkey: @no, //             //avvideoh264entropymodekey: avvideoh264entropymodecavlc, //             //avvideoexpectedsourceframeratekey: @(30), //             //avvideoaveragenondroppableframeratekey: @(30) //        } //    };     nsdictionary* settings = @{                                avvideocodeckey: avvideocodech264,                                avvideowidthkey: [nsnumber numberwithint:width],                                avvideoheightkey: [nsnumber numberwithint:height],                                avvideocompressionpropertieskey: @{                                        avvideoaveragebitratekey: [nsnumber numberwithint:bitrate],                                        avvideomaxkeyframeintervalkey: @(150),                                        avvideoprofilelevelkey: avvideoprofilelevelh264baselineautolevel,                                        avvideoallowframereorderingkey: @no,                                        avvideoh264entropymodekey: avvideoh264entropymodecavlc,                                        avvideoexpectedsourceframeratekey: @(30),                                        avvideoaveragenondroppableframeratekey: @(30)                                        }                                };      audiochannellayout acl;     bzero( &acl, sizeof(acl));     acl.mchannellayouttag = kaudiochannellayouttag_mono;      nsdictionary *audiooutputsettings = [nsdictionary dictionarywithobjectsandkeys:                            [ nsnumber numberwithint: kaudioformatmpeg4aac ], avformatidkey,                            [ nsnumber numberwithint: 1 ], avnumberofchannelskey,                            [ nsnumber numberwithfloat: 44100.0 ], avsampleratekey,                            [ nsnumber numberwithint: 64000 ], avencoderbitratekey,                            [ nsdata datawithbytes: &acl length: sizeof( acl ) ], avchannellayoutkey,                            nil];      audiowriterinput = [avassetwriterinput assetwriterinputwithmediatype:avmediatypeaudio outputsettings:audiooutputsettings];     audiowriterinput.expectsmediadatainrealtime=yes;     _writerinput = [avassetwriterinput assetwriterinputwithmediatype:avmediatypevideo outputsettings:settings];     _writerinput.expectsmediadatainrealtime = yes;      [_writer addinput:audiowriterinput];     [_writer addinput:_writerinput]; }