pcm-dvd: Support channel configuration changes

The sample buffering logic does not take into account that the blocksize
could change. Reset the buffer if the channel configuration changes,
since if there are leftover samples, it is most likely a broken or
misconcatenated stream. This could lead to negative numbers for
missing_samples during decoding.

Thanks to Michael Niedermeyer for pointing these out.

libavcodec/pcm-dvd.c

@@ -46,7 +46,6 @@ static av_cold int pcm_dvd_decode_init(AVCodecContext *avctx)
     /* reserve space for 8 channels, 3 bytes/sample, 4 samples/block */
     if (!(s->extra_samples = av_malloc(8 * 3 * 4)))
         return AVERROR(ENOMEM);
-    s->extra_sample_count = 0;
 
     return 0;
 }
@@ -81,6 +80,9 @@ static int pcm_dvd_parse_header(AVCodecContext *avctx, const uint8_t *header)
      * header[2] dynamic range control (0x80 = off)
      */
 
+    /* Discard potentially existing leftover samples from old channel layout */
+    s->extra_sample_count = 0;
+
     /* get the sample depth and derive the sample format from it */
     avctx->bits_per_coded_sample = 16 + (header[1] >> 6 & 3) * 4;
     if (avctx->bits_per_coded_sample == 28) {