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LFE channel should always be counted for AC-4 object-based content on MPEG-4 layer #1943

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ybai001 committed Dec 3, 2024
commit 1df0ee2052d43af5480f5f5c8827c9460b80c6bf
Original file line number Diff line number Diff line change
@@ -412,12 +412,12 @@ public static Format parseAc4AnnexEFormat(
} else {
// The ETSI TS 103 190-2 V1.2.1 (2018-02) specification defines the parameter
// n_umx_objects_minus1 in Annex E (E.11.11) to specify the number of fullband objects. While
// the elementary stream specification (section 6.3.2.8.1) provides information about the
// presence of an LFE channel within the set of dynamic objects, this detail is not explicitly
// stated in the ISO Base Media File Format (Annex E). However, current implementation
// practices consistently include the LFE channel when creating an A-JOC substream. As a
// result, it has been decided that when interpreting the ISO Base Media File Format, the LFE
// channel should always be counted as part of the total channel count.
// the elementary stream specification (section 6.3.2.8.1 and 6.3.2.10.4) provides information
// about the presence of an LFE channel within the set of dynamic objects, this detail is not
// explicitly stated in the ISO Base Media File Format (Annex E). However, current
// implementation practices consistently include the LFE channel when creating an object-based
// substream. As a result, it has been decided that when interpreting the ISO Base Media File
// Format, the LFE channel should always be counted as part of the total channel count.
channelCount = ac4Presentation.numOfUmxObjects + 1; // Here "1" stands for LFE channel
// TODO: There is a bug in ETSI TS 103 190-2 V1.2.1 (2018-02), E.11.11
// For AC-4 level 4 stream, the intention is to set 19 to n_umx_objects_minus1 but it is