From e10fccf62a36e09b54ad6ea3d5fa6638f298d5ae Mon Sep 17 00:00:00 2001 From: Anssi Hannula Date: Tue, 17 Dec 2013 23:04:31 +0200 Subject: [PATCH] avcodec/aacdec: default to non-wide 7.1 in non-strict mode AAC specification has 7.1(wide) as a default layout for 8-channel streams (channel config 7). However, at least Nero AAC encoder encodes non-wide 7.1 streams using the default channel config 7, mapping the side channels of the original audio stream to the second AAC_CHANNEL_FRONT pair in the AAC stream. Similarly, e.g. FAAD decodes the second AAC_CHANNEL_FRONT pair as side channels, therefore decoding the incorrect streams as if they were correct (and as the encoder intended). FFmpeg currently decodes such files by-the-spec, i.e. after decoding the original front pair will be in AV_CH_FRONT_x_OF_CENTER and the original side pair will be in AV_CH_FRONT_x. As actual intended 7.1(wide) streams are very rare while misencoded 7.1 files actually exist in the wild, default to assuming a 7.1 layout was intended unless in strict mode. Fixes playback of e.g. 8_Channel_ID.m4a in samples. Signed-off-by: Anssi Hannula Signed-off-by: Michael Niedermayer --- libavcodec/aacdec.c | 19 +++++++++++++++++++ 1 file changed, 19 insertions(+) diff --git a/libavcodec/aacdec.c b/libavcodec/aacdec.c index 1fb91853d0..1e15cb45fc 100644 --- a/libavcodec/aacdec.c +++ b/libavcodec/aacdec.c @@ -534,6 +534,25 @@ static int set_default_channel_config(AVCodecContext *avctx, *tags = tags_per_config[channel_config]; memcpy(layout_map, aac_channel_layout_map[channel_config - 1], *tags * sizeof(*layout_map)); + + /* + * AAC specification has 7.1(wide) as a default layout for 8-channel streams. + * However, at least Nero AAC encoder encodes 7.1 streams using the default + * channel config 7, mapping the side channels of the original audio stream + * to the second AAC_CHANNEL_FRONT pair in the AAC stream. Similarly, e.g. FAAD + * decodes the second AAC_CHANNEL_FRONT pair as side channels, therefore decoding + * the incorrect streams as if they were correct (and as the encoder intended). + * + * As actual intended 7.1(wide) streams are very rare, default to assuming a + * 7.1 layout was intended. + */ + if (channel_config == 7 && avctx->strict_std_compliance < FF_COMPLIANCE_STRICT) { + av_log(avctx, AV_LOG_INFO, "Assuming an incorrectly encoded 7.1 channel layout" + " instead of a spec-compliant 7.1(wide) layout, use -strict %d to decode" + " according to the specification instead.\n", FF_COMPLIANCE_STRICT); + layout_map[2][2] = AAC_CHANNEL_SIDE; + } + return 0; }