avcodec: Set time_base for audio encoders, too

This is required when encoding audio in libav 0.8, otherwise
it will crash due to a division by zero.
Signed-off-by: Jean-Baptiste Kempf <jb@videolan.org>
(cherry picked from commit 25fc1243b81a46a100e37db5ec477bd5096b979a)
Signed-off-by: Jean-Baptiste Kempf <jb@videolan.org>

modules/codec/avcodec/encoder.c

@@ -607,6 +607,8 @@ int OpenEncoder( vlc_object_t *p_this )
                                     SAMPLE_FMT_S16;
         p_enc->fmt_in.i_codec  = VLC_CODEC_S16N;
         p_context->sample_rate = p_enc->fmt_out.audio.i_rate;
+        p_context->time_base.num = 1;
+        p_context->time_base.den = p_context->sample_rate;
         p_context->channels    = p_enc->fmt_out.audio.i_channels;
 
         if ( p_enc->fmt_out.i_codec == VLC_CODEC_MP4A )

modules/stream_out/switcher.c

@@ -382,6 +382,8 @@ static sout_stream_id_t *Add( sout_stream_t *p_stream, es_format_t *p_fmt )
         }
 
         id->ff_enc_c->sample_rate = p_fmt->audio.i_rate;
+        id->ff_enc_c->time_base.num = 1;
+        id->ff_enc_c->time_base.den = p_fmt->audio.i_rate;
         id->ff_enc_c->channels    = p_fmt->audio.i_channels;
         id->ff_enc_c->bit_rate    = p_fmt->i_bitrate;