[xcode] Fix calculation of estimated wav sizes (causing M1001 crash)

Fix regression from commit 3ee9204 where wav size calculation was changed. The
new method caused Soundbridge M1001 to reboot, and the likely cause seems to be
that the sizes in the wav header may not be multiples of channels x
bytes_per_sample, so typically 4.

Resolves #1770

src/transcode.c

@@ -562,26 +562,22 @@ dummy_seek(void *arg, int64_t offset, enum transcode_seek_type type)
 }
 
 static off_t
-size_estimate(enum transcode_profile profile, int bit_rate, int sample_rate, int bytes_per_sample, int channels, int len_ms)
+size_estimate(enum transcode_profile profile, uint32_t bit_rate, uint32_t sample_rate, uint16_t bytes_per_sample, uint16_t channels, uint32_t len_ms)
 {
-  off_t bytes;
+  off_t bytes = 0;
+  uint64_t nsamples;
 
-  // If the source has a number of samples that doesn't match an even len_ms
-  // then the length may have been rounded up. We prefer an estimate that is on
-  // the low side, otherwise ffprobe won't trust the length from our wav header.
-  if (len_ms > 0)
-    len_ms -= 1;
-  else
+  if (len_ms == 0)
     len_ms = 3 * 60 * 1000;
 
+  nsamples = (uint64_t)sample_rate * (uint64_t)len_ms / 1000 + 1; // The +1 is to round up
+
   if (profile == XCODE_WAV)
-    bytes = (int64_t)len_ms * channels * bytes_per_sample * sample_rate / 1000 + WAV_HEADER_LEN;
+    bytes = nsamples * channels * bytes_per_sample + WAV_HEADER_LEN;
   else if (profile == XCODE_MP3)
-    bytes = (int64_t)len_ms * bit_rate / 8000;
+    bytes = (uint64_t)len_ms * (uint64_t)bit_rate / 8000;
   else if (profile == XCODE_MP4_ALAC)
-    bytes = (int64_t)len_ms * channels * bytes_per_sample * sample_rate / 1000 / 2; // FIXME
-  else
-    bytes = -1;
+    bytes = nsamples * channels * bytes_per_sample / 2; // FIXME
 
   return bytes;
 }
@@ -1095,24 +1091,22 @@ avio_evbuffer_close(AVIOContext *s)
 /* ----------------------- CUSTOM HEADER GENERATION ------------------------ */
 
 static int
-make_wav_header(struct evbuffer **wav_header, int sample_rate, int bytes_per_sample, int channels, off_t bytes_total)
+make_wav_header(struct evbuffer **wav_header, uint32_t sample_rate, uint16_t bytes_per_sample, uint16_t channels, uint32_t bytes_total)
 {
   uint8_t header[WAV_HEADER_LEN];
 
-  uint32_t wav_size = bytes_total - WAV_HEADER_LEN;
-
   memcpy(header, "RIFF", 4);
-  add_le32(header + 4, 36 + wav_size);
+  add_le32(header + 4, bytes_total - 8); // Total file size - 8 bytes as defined by the format
   memcpy(header + 8, "WAVEfmt ", 8);
   add_le32(header + 16, 16);
-  add_le16(header + 20, 1);
+  add_le16(header + 20, 1); // AudioFormat (PCM)
   add_le16(header + 22, channels);     /* channels */
   add_le32(header + 24, sample_rate);  /* samplerate */
   add_le32(header + 28, sample_rate * channels * bytes_per_sample); /* byte rate */
   add_le16(header + 32, channels * bytes_per_sample);               /* block align */
   add_le16(header + 34, 8 * bytes_per_sample);                      /* bits per sample */
   memcpy(header + 36, "data", 4);
-  add_le32(header + 40, wav_size);
+  add_le32(header + 40, bytes_total - WAV_HEADER_LEN);
 
   *wav_header = evbuffer_new();
   evbuffer_add(*wav_header, header, sizeof(header));