loliball/media
1
0
Fork 0
mirror of https://github.com/androidx/media.git synced 2025-05-17 12:39:52 +08:00
Code Issues Actions Packages Projects Releases Wiki Activity

Clarify SSA and SubRip docs in MatroskaExtractor

Browse Source 
The handling of times wasn't really clear to me, hopefully this more
exhaustive documentation helps a bit.

Also assert the end timecode is the 'correct' length for the format.

PiperOrigin-RevId: 279922369
This commit is contained in:
ibaker 2019-11-12 10:54:49 +00:00 committed by Oliver Woodman
parent 2faef48302
commit b43db3bceb
1 changed files with 50 additions and 19 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

69
library/core/src/main/java/com/google/android/exoplayer2/extractor/mkv/MatroskaExtractor.java
View File

@ -236,14 +236,21 @@ public class MatroskaExtractor implements Extractor {
private static final int FOURCC_COMPRESSION_VC1 = 0x31435657; private static final int FOURCC_COMPRESSION_VC1 = 0x31435657;
/** /**
* A template for the prefix that must be added to each subrip sample. The 12 byte end timecode * A template for the prefix that must be added to each subrip sample.
* starting at {@link #SUBRIP_PREFIX_END_TIMECODE_OFFSET} is set to a dummy value, and must be *
* replaced with the duration of the subtitle. * <p>The display time of each subtitle is passed as {@code timeUs} to {@link
* <p> * TrackOutput#sampleMetadata}. The start and end timecodes in this template are relative to
* Equivalent to the UTF-8 string: "1\n00:00:00,000 --> 00:00:00,000\n". * {@code timeUs}. Hence the start timecode is always zero. The 12 byte end timecode starting at
* {@link #SUBRIP_PREFIX_END_TIMECODE_OFFSET} is set to a dummy value, and must be replaced with
* the duration of the subtitle.
*
* <p>Equivalent to the UTF-8 string: "1\n00:00:00,000 --> 00:00:00,000\n".
*/ */
private static final byte[] SUBRIP_PREFIX = new byte[] {49, 10, 48, 48, 58, 48, 48, 58, 48, 48, private static final byte[] SUBRIP_PREFIX =
44, 48, 48, 48, 32, 45, 45, 62, 32, 48, 48, 58, 48, 48, 58, 48, 48, 44, 48, 48, 48, 10}; new byte[] {
49, 10, 48, 48, 58, 48, 48, 58, 48, 48, 44, 48, 48, 48, 32, 45, 45, 62, 32, 48, 48, 58, 48,
48, 58, 48, 48, 44, 48, 48, 48, 10
};
/** /**
* The byte offset of the end timecode in {@link #SUBRIP_PREFIX}. * The byte offset of the end timecode in {@link #SUBRIP_PREFIX}.
*/ */
@ -272,14 +279,21 @@ public class MatroskaExtractor implements Extractor {
private static final byte[] SSA_DIALOGUE_FORMAT = Util.getUtf8Bytes("Format: Start, End, " private static final byte[] SSA_DIALOGUE_FORMAT = Util.getUtf8Bytes("Format: Start, End, "
+ "ReadOrder, Layer, Style, Name, MarginL, MarginR, MarginV, Effect, Text"); + "ReadOrder, Layer, Style, Name, MarginL, MarginR, MarginV, Effect, Text");
/** /**
* A template for the prefix that must be added to each SSA sample. The 10 byte end timecode * A template for the prefix that must be added to each SSA sample.
* starting at {@link #SSA_PREFIX_END_TIMECODE_OFFSET} is set to a dummy value, and must be *
* replaced with the duration of the subtitle. * <p>The display time of each subtitle is passed as {@code timeUs} to {@link
* <p> * TrackOutput#sampleMetadata}. The start and end timecodes in this template are relative to
* Equivalent to the UTF-8 string: "Dialogue: 0:00:00:00,0:00:00:00,". * {@code timeUs}. Hence the start timecode is always zero. The 12 byte end timecode starting at
* {@link #SUBRIP_PREFIX_END_TIMECODE_OFFSET} is set to a dummy value, and must be replaced with
* the duration of the subtitle.
*
* <p>Equivalent to the UTF-8 string: "Dialogue: 0:00:00:00,0:00:00:00,".
*/ */
private static final byte[] SSA_PREFIX = new byte[] {68, 105, 97, 108, 111, 103, 117, 101, 58, 32, private static final byte[] SSA_PREFIX =
48, 58, 48, 48, 58, 48, 48, 58, 48, 48, 44, 48, 58, 48, 48, 58, 48, 48, 58, 48, 48, 44}; new byte[] {
68, 105, 97, 108, 111, 103, 117, 101, 58, 32, 48, 58, 48, 48, 58, 48, 48, 58, 48, 48, 44,
48, 58, 48, 48, 58, 48, 48, 58, 48, 48, 44
};
/** /**
* The byte offset of the end timecode in {@link #SSA_PREFIX}. * The byte offset of the end timecode in {@link #SSA_PREFIX}.
*/ */
@ -1468,16 +1482,32 @@ public class MatroskaExtractor implements Extractor {
private void commitSubtitleSample(Track track, String timecodeFormat, int endTimecodeOffset, private void commitSubtitleSample(Track track, String timecodeFormat, int endTimecodeOffset,
long lastTimecodeValueScalingFactor, byte[] emptyTimecode) { long lastTimecodeValueScalingFactor, byte[] emptyTimecode) {
setSampleDuration(subtitleSample.data, blockDurationUs, timecodeFormat, endTimecodeOffset, setSubtitleSampleDuration(
lastTimecodeValueScalingFactor, emptyTimecode); subtitleSample.data,
blockDurationUs,
timecodeFormat,
endTimecodeOffset,
lastTimecodeValueScalingFactor,
emptyTimecode);
// Note: If we ever want to support DRM protected subtitles then we'll need to output the // Note: If we ever want to support DRM protected subtitles then we'll need to output the
// appropriate encryption data here. // appropriate encryption data here.
track.output.sampleData(subtitleSample, subtitleSample.limit()); track.output.sampleData(subtitleSample, subtitleSample.limit());
sampleBytesWritten += subtitleSample.limit(); sampleBytesWritten += subtitleSample.limit();
} }
private static void setSampleDuration(byte[] subripSampleData, long durationUs, /**
String timecodeFormat, int endTimecodeOffset, long lastTimecodeValueScalingFactor, * Formats {@code durationUs} using {@code timecodeFormat}, and sets it as the end timecode in
* {@code subtitleSampleData}.
*
* <p>See documentation on {@link #SSA_DIALOGUE_FORMAT} and {@link #SUBRIP_PREFIX} for why we use
* the duration as the end timecode.
*/
private static void setSubtitleSampleDuration(
byte[] subtitleSampleData,
long durationUs,
String timecodeFormat,
int endTimecodeOffset,
long lastTimecodeValueScalingFactor,
byte[] emptyTimecode) { byte[] emptyTimecode) {
byte[] timeCodeData; byte[] timeCodeData;
if (durationUs == C.TIME_UNSET) { if (durationUs == C.TIME_UNSET) {
@ -1493,7 +1523,8 @@ public class MatroskaExtractor implements Extractor {
timeCodeData = Util.getUtf8Bytes(String.format(Locale.US, timecodeFormat, hours, minutes, timeCodeData = Util.getUtf8Bytes(String.format(Locale.US, timecodeFormat, hours, minutes,
seconds, lastValue)); seconds, lastValue));
} }
System.arraycopy(timeCodeData, 0, subripSampleData, endTimecodeOffset, emptyTimecode.length); Assertions.checkState(timeCodeData.length == emptyTimecode.length);
System.arraycopy(timeCodeData, 0, subtitleSampleData, endTimecodeOffset, timeCodeData.length);
} }
/** /**