don't just pass 0 for samples in Ogg/FLAC callback

This is a fix for #661

include/FLAC/stream_encoder.h

@@ -538,11 +538,16 @@ typedef FLAC__StreamEncoderReadStatus (*FLAC__StreamEncoderReadCallback)(const F
  *  callback is being called to write metadata.
  *
  * \note
- * Unlike when writing to native FLAC, when writing to Ogg FLAC the
- * write callback will be called twice when writing each audio
- * frame; once for the page header, and once for the page body.
- * When writing the page header, the \a samples argument to the
- * write callback will be \c 0.
+ * Unlike when writing to native FLAC, when writing to Ogg FLAC the write
+ * callback will be called at least twice when writing each audio frame; once
+ * for the page header and once for the page body, possibly repeating this
+ * pair of calls several times in a batch with the same value of
+ * \a current_frame.  When writing the page header, as well as in all but the
+ * first page body write of the batch, the \a samples argument to the write
+ * callback will be \c 0. The full number of samples of the batch will be
+ * passed in the first page body write. Furthermore, it is possible that a few
+ * of these samples are retained in an internal Ogg encoding buffer and not
+ * actually encoded until the next batch.
  *
  * \note In general, FLAC__StreamEncoder functions which change the
  * state should not be called on the \a encoder while in the callback.

src/libFLAC/include/private/ogg_encoder_aspect.h

@@ -49,6 +49,7 @@ typedef struct FLAC__OggEncoderAspect {
 	FLAC__bool seen_magic; /* true if we've seen the fLaC magic in the write callback yet */
 	FLAC__bool is_first_packet;
 	FLAC__uint64 samples_written;
+	uint32_t samples_in_submit_buffer;
 } FLAC__OggEncoderAspect;
 
 void FLAC__ogg_encoder_aspect_set_serial_number(FLAC__OggEncoderAspect *aspect, long value);

src/libFLAC/ogg_encoder_aspect.c

@@ -57,6 +57,7 @@ FLAC__bool FLAC__ogg_encoder_aspect_init(FLAC__OggEncoderAspect *aspect)
 	aspect->seen_magic = false;
 	aspect->is_first_packet = true;
 	aspect->samples_written = 0;
+	aspect->samples_in_submit_buffer = 0;
 
 	return true;
 }
@@ -192,21 +193,27 @@ FLAC__StreamEncoderWriteStatus FLAC__ogg_encoder_aspect_write_callback_wrapper(F
 		if(ogg_stream_packetin(&aspect->stream_state, &packet) != 0)
 			return FLAC__STREAM_ENCODER_WRITE_STATUS_FATAL_ERROR;
 
-		/*@@@ can't figure out a way to pass a useful number for 'samples' to the write_callback, so we'll just pass 0 */
+		/* For a batch of write_callback calls associated with the same current_frame, pass the number of samples in the
+		 * first non-metadata page body call, and then set to zero in case there are more iterations of the while loop (so
+		 * as not to give the impression of more samples being processed).
+		 */
+		aspect->samples_in_submit_buffer += samples;
 		if(is_metadata) {
 			while(ogg_stream_flush(&aspect->stream_state, &aspect->page) != 0) {
 				if(write_callback(encoder, aspect->page.header, aspect->page.header_len, 0, current_frame, client_data) != FLAC__STREAM_ENCODER_WRITE_STATUS_OK)
 					return FLAC__STREAM_ENCODER_WRITE_STATUS_FATAL_ERROR;
-				if(write_callback(encoder, aspect->page.body, aspect->page.body_len, 0, current_frame, client_data) != FLAC__STREAM_ENCODER_WRITE_STATUS_OK)
+				if(write_callback(encoder, aspect->page.body, aspect->page.body_len, aspect->samples_in_submit_buffer, current_frame, client_data) != FLAC__STREAM_ENCODER_WRITE_STATUS_OK)
 					return FLAC__STREAM_ENCODER_WRITE_STATUS_FATAL_ERROR;
+				aspect->samples_in_submit_buffer = 0;
 			}
 		}
 		else {
 			while(ogg_stream_pageout(&aspect->stream_state, &aspect->page) != 0) {
 				if(write_callback(encoder, aspect->page.header, aspect->page.header_len, 0, current_frame, client_data) != FLAC__STREAM_ENCODER_WRITE_STATUS_OK)
 					return FLAC__STREAM_ENCODER_WRITE_STATUS_FATAL_ERROR;
-				if(write_callback(encoder, aspect->page.body, aspect->page.body_len, 0, current_frame, client_data) != FLAC__STREAM_ENCODER_WRITE_STATUS_OK)
+				if(write_callback(encoder, aspect->page.body, aspect->page.body_len, aspect->samples_in_submit_buffer, current_frame, client_data) != FLAC__STREAM_ENCODER_WRITE_STATUS_OK)
 					return FLAC__STREAM_ENCODER_WRITE_STATUS_FATAL_ERROR;
+				aspect->samples_in_submit_buffer = 0;
 			}
 		}
 	}