From 5ca137c73cda80f4c1f43bbcd627b4eda4a169cd Mon Sep 17 00:00:00 2001
From: Max Kellermann <max@musicpd.org>
Date: Wed, 1 Jul 2020 20:51:44 +0200
Subject: [PATCH] decoder/opus: add API docs
---
src/decoder/plugins/OpusDecoderPlugin.cxx | 21 ++++++++++++++++++++-
1 file changed, 20 insertions(+), 1 deletion(-)
diff --git a/src/decoder/plugins/OpusDecoderPlugin.cxx b/src/decoder/plugins/OpusDecoderPlugin.cxx
index 9043d76c0..88e8098f0 100644
--- a/src/decoder/plugins/OpusDecoderPlugin.cxx
+++ b/src/decoder/plugins/OpusDecoderPlugin.cxx
@@ -75,7 +75,18 @@ class MPDOpusDecoder final : public OggDecoder {
OpusDecoder *opus_decoder = nullptr;
opus_int16 *output_buffer = nullptr;
- unsigned pre_skip, skip;
+ /**
+ * The pre-skip value from the Opus header. Initialized by
+ * OnOggBeginning().
+ */
+ unsigned pre_skip;
+
+ /**
+ * The number of decoded samples which shall be skipped. At
+ * the beginning of the file, this gets set to #pre_skip (by
+ * OnOggBeginning()), and may also be set while seeking.
+ */
+ unsigned skip;
/**
* If non-zero, then a previous Opus stream has been found
@@ -240,6 +251,7 @@ MPDOpusDecoder::HandleAudio(const ogg_packet &packet)
opus_strerror(nframes));
if (nframes > 0) {
+ /* apply the "skip" value */
if (skip >= (unsigned)nframes) {
skip -= nframes;
return;
@@ -250,6 +262,7 @@ MPDOpusDecoder::HandleAudio(const ogg_packet &packet)
nframes -= skip;
skip = 0;
+ /* submit decoded samples to the DecoderClient */
const size_t nbytes = nframes * frame_size;
auto cmd = client.SubmitData(input_stream,
data, nbytes,
@@ -274,6 +287,12 @@ MPDOpusDecoder::Seek(uint64_t where_frame)
try {
SeekGranulePos(where_granulepos);
+
+ /* since all frame numbers are offset by the file's
+ pre-skip value, we need to apply it here as well;
+ we could just seek to "where_frame+pre_skip" as
+ well, but I think by decoding those samples and
+ discard them, we're safer */
skip = pre_skip;
return true;
} catch (...) {