Merge changes from topic "metadata-trackfix"
* changes:
MPEG4Extractor: Read out the Metadata track correctly.
MPEG4Writer: Fix the bug in MPEG4 metadata track.
diff --git a/media/extractors/mp4/MPEG4Extractor.cpp b/media/extractors/mp4/MPEG4Extractor.cpp
index c4b539d..390ba43 100644
--- a/media/extractors/mp4/MPEG4Extractor.cpp
+++ b/media/extractors/mp4/MPEG4Extractor.cpp
@@ -1553,9 +1553,40 @@
return ERROR_IO;
}
- String8 mimeFormat((const char *)(buffer.get()), chunk_data_size);
- AMediaFormat_setString(mLastTrack->meta, AMEDIAFORMAT_KEY_MIME, mimeFormat.string());
+ // Prior to API 29, the metadata track was not compliant with ISO/IEC
+ // 14496-12-2015. This led to some ISO-compliant parsers failing to read the
+ // metatrack. As of API 29 and onwards, a change was made to metadata track to
+ // make it compliant with the standard. The workaround is to write the
+ // null-terminated mime_format string twice. This allows compliant parsers to
+ // read the missing reserved, data_reference_index, and content_encoding fields
+ // from the first mime_type string. The actual mime_format field would then be
+ // read correctly from the second string. The non-compliant Android frameworks
+ // from API 28 and earlier would still be able to read the mime_format correctly
+ // as it would only read the first null-terminated mime_format string. To enable
+ // reading metadata tracks generated from both the non-compliant and compliant
+ // formats, a check needs to be done to see which format is used.
+ int null_pos = 0;
+ const unsigned char *str = buffer.get();
+ while (null_pos < chunk_data_size) {
+ if (*(str + null_pos) == '\0') {
+ break;
+ }
+ ++null_pos;
+ }
+ if (null_pos == chunk_data_size - 1) {
+ // This is not a standard ompliant metadata track.
+ String8 mimeFormat((const char *)(buffer.get()), chunk_data_size);
+ AMediaFormat_setString(mLastTrack->meta,
+ AMEDIAFORMAT_KEY_MIME, mimeFormat.string());
+ } else {
+ // This is a standard compliant metadata track.
+ String8 contentEncoding((const char *)(buffer.get() + 8));
+ String8 mimeFormat((const char *)(buffer.get() + 8 + contentEncoding.size() + 1),
+ chunk_data_size - 8 - contentEncoding.size() - 1);
+ AMediaFormat_setString(mLastTrack->meta,
+ AMEDIAFORMAT_KEY_MIME, mimeFormat.string());
+ }
break;
}
diff --git a/media/libstagefright/MPEG4Writer.cpp b/media/libstagefright/MPEG4Writer.cpp
index 6ff3d78..a48466a 100644
--- a/media/libstagefright/MPEG4Writer.cpp
+++ b/media/libstagefright/MPEG4Writer.cpp
@@ -3674,6 +3674,29 @@
TRESPASS();
}
mOwner->beginBox(fourcc); // TextMetaDataSampleEntry
+
+ // HACK to make the metadata track compliant with the ISO standard.
+ //
+ // Metadata track is added from API 26 and the original implementation does not
+ // fully followed the TextMetaDataSampleEntry specified in ISO/IEC 14496-12-2015
+ // in that only the mime_format is written out. content_encoding and
+ // data_reference_index have not been written out. This leads to the failure
+ // when some MP4 parser tries to parse the metadata track according to the
+ // standard. The hack here will make the metadata track compliant with the
+ // standard while still maintaining backwards compatibility. This would enable
+ // Android versions before API 29 to be able to read out the standard compliant
+ // Metadata track generated with Android API 29 and upward. The trick is based
+ // on the fact that the Metadata track must start with prefix “application/” and
+ // those missing fields are not used in Android's Metadata track. By writting
+ // out the mime_format twice, the first mime_format will be used to fill out the
+ // missing reserved, data_reference_index and content encoding fields. On the
+ // parser side, the extracter before API 29 will read out the first mime_format
+ // correctly and drop the second mime_format. The extractor from API 29 will
+ // check if the reserved, data_reference_index and content encoding are filled
+ // with “application” to detect if this is a standard compliant metadata track
+ // and read out the data accordingly.
+ mOwner->writeCString(mime);
+
mOwner->writeCString(mime); // metadata mime_format
mOwner->endBox(); // mett
}