decoder/mad: subtract libmad decoder delay from LAME encoder padding

Apparently, libmad not only inserts 529 samples of silence at the beginning of the file, but also removes them at the end. This solves the last piece of https://github.com/MusicPlayerDaemon/MPD/issues/601 Closes https://github.com/MusicPlayerDaemon/MPD/issues/601

decoder/mad: subtract libmad decoder delay from LAME encoder padding
952c7932 · Max Kellermann · 3e3d8c7f · 952c7932 · 952c7932
Commit 952c7932 authored Aug 03, 2019 by Max Kellermann
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NEWS NEWS +1 -0

MadDecoderPlugin.cxx src/decoder/plugins/MadDecoderPlugin.cxx +8 -0

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--- a/NEWS
+++ b/NEWS
 ver 0.21.12 (not yet released)
 * decoder
  - mad: update bit rate after seeking
+  - mad: fix several bugs preventing the plugin from decoding the last frame
  - opus: ignore case in replay gain tag names
  - opus, vorbis: decode the "end of stream" packet
 * output

--- a/src/decoder/plugins/MadDecoderPlugin.cxx
+++ b/src/decoder/plugins/MadDecoderPlugin.cxx
@@ -749,9 +749,17 @@ MadDecoder::DecodeFirstFrame(Tag *tag) noexcept
 		struct lame lame;
 		if (parse_lame(&lame, &ptr, &bitlen)) {
 			if (gapless_playback && input_stream.IsSeekable()) {
+				/* libmad inserts 529 samples of
+				   silence at the beginning and
+				   removes those 529 samples at the
+				   end */
 				drop_start_samples = lame.encoder_delay +
 				                           DECODERDELAY;
 				drop_end_samples = lame.encoder_padding;
+				if (drop_end_samples > DECODERDELAY)
+					drop_end_samples -= DECODERDELAY;
+				else
+					drop_end_samples = 0;
 			}
 			/* Album gain isn't currently used.  See comment in