SubripParser.java
/*
* Copyright (C) 2016 The Android Open Source Project
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package androidx.media3.extractor.text.subrip;
import static androidx.annotation.VisibleForTesting.PRIVATE;
import android.text.Html;
import android.text.Spanned;
import android.text.TextUtils;
import androidx.annotation.Nullable;
import androidx.annotation.VisibleForTesting;
import androidx.media3.common.C;
import androidx.media3.common.Format;
import androidx.media3.common.Format.CueReplacementBehavior;
import androidx.media3.common.text.Cue;
import androidx.media3.common.util.Assertions;
import androidx.media3.common.util.Consumer;
import androidx.media3.common.util.Log;
import androidx.media3.common.util.ParsableByteArray;
import androidx.media3.common.util.UnstableApi;
import androidx.media3.extractor.text.CuesWithTiming;
import androidx.media3.extractor.text.SubtitleParser;
import com.google.common.base.Charsets;
import com.google.common.collect.ImmutableList;
import java.nio.charset.Charset;
import java.util.ArrayList;
import java.util.List;
import java.util.regex.Matcher;
import java.util.regex.Pattern;
/** A {@link SubtitleParser} for SubRip. */
@UnstableApi
public final class SubripParser implements SubtitleParser {
/**
* The {@link CueReplacementBehavior} for consecutive {@link CuesWithTiming} emitted by this
* implementation.
*/
public static final @CueReplacementBehavior int CUE_REPLACEMENT_BEHAVIOR =
Format.CUE_REPLACEMENT_BEHAVIOR_MERGE;
// Fractional positions for use when alignment tags are present.
private static final float START_FRACTION = 0.08f;
private static final float END_FRACTION = 1 - START_FRACTION;
private static final float MID_FRACTION = 0.5f;
private static final String TAG = "SubripParser";
// Some SRT files don't include hours or milliseconds in the timecode, so we use optional groups.
private static final String SUBRIP_TIMECODE = "(?:(\d+):)?(\d+):(\d+)(?:,(\d+))?";
private static final Pattern SUBRIP_TIMING_LINE =
Pattern.compile("\s*(" + SUBRIP_TIMECODE + ")\s*-->\s*(" + SUBRIP_TIMECODE + ")\s*");
// NOTE: Android Studio's suggestion to simplify '\}' is incorrect [internal: b/144480183].
private static final Pattern SUBRIP_TAG_PATTERN = Pattern.compile("\{\\.*?\}");
private static final String SUBRIP_ALIGNMENT_TAG = "\{\\an[1-9]\}";
// Alignment tags for SSA V4+.
private static final String ALIGN_BOTTOM_LEFT = "{\an1}";
private static final String ALIGN_BOTTOM_MID = "{\an2}";
private static final String ALIGN_BOTTOM_RIGHT = "{\an3}";
private static final String ALIGN_MID_LEFT = "{\an4}";
private static final String ALIGN_MID_MID = "{\an5}";
private static final String ALIGN_MID_RIGHT = "{\an6}";
private static final String ALIGN_TOP_LEFT = "{\an7}";
private static final String ALIGN_TOP_MID = "{\an8}";
private static final String ALIGN_TOP_RIGHT = "{\an9}";
private final StringBuilder textBuilder;
private final ArrayList<String> tags;
private final ParsableByteArray parsableByteArray;
public SubripParser() {
textBuilder = new StringBuilder();
tags = new ArrayList<>();
parsableByteArray = new ParsableByteArray();
}
@Override
public @CueReplacementBehavior int getCueReplacementBehavior() {
return CUE_REPLACEMENT_BEHAVIOR;
}
@Override
public void parse(
byte[] data,
int offset,
int length,
OutputOptions outputOptions,
Consumer<CuesWithTiming> output) {
parsableByteArray.reset(data, /* limit= */ offset + length);
parsableByteArray.setPosition(offset);
Charset charset = detectUtfCharset(parsableByteArray);
@Nullable
List<CuesWithTiming> cuesWithTimingBeforeRequestedStartTimeUs =
outputOptions.startTimeUs != C.TIME_UNSET && outputOptions.outputAllCues
? new ArrayList<>()
: null;
@Nullable String currentLine;
while ((currentLine = parsableByteArray.readLine(charset)) != null) {
if (currentLine.length() == 0) {
// Skip blank lines.
continue;
}
// Parse and check the index line.
try {
Integer.parseInt(currentLine);
} catch (NumberFormatException e) {
Log.w(TAG, "Skipping invalid index: " + currentLine);
continue;
}
// Read and parse the timing line.
currentLine = parsableByteArray.readLine(charset);
if (currentLine == null) {
Log.w(TAG, "Unexpected end");
break;
}
long startTimeUs;
long endTimeUs;
Matcher matcher = SUBRIP_TIMING_LINE.matcher(currentLine);
if (matcher.matches()) {
startTimeUs = parseTimecode(matcher, /* groupOffset= */ 1);
endTimeUs = parseTimecode(matcher, /* groupOffset= */ 6);
} else {
Log.w(TAG, "Skipping invalid timing: " + currentLine);
continue;
}
// Read and parse the text and tags.
textBuilder.setLength(0);
tags.clear();
currentLine = parsableByteArray.readLine(charset);
while (!TextUtils.isEmpty(currentLine)) {
if (textBuilder.length() > 0) {
textBuilder.append("<br>");
}
textBuilder.append(processLine(currentLine, tags));
currentLine = parsableByteArray.readLine(charset);
}
Spanned text = Html.fromHtml(textBuilder.toString());
@Nullable String alignmentTag = null;
for (int i = 0; i < tags.size(); i++) {
String tag = tags.get(i);
if (tag.matches(SUBRIP_ALIGNMENT_TAG)) {
alignmentTag = tag;
// Subsequent alignment tags should be ignored.
break;
}
}
if (outputOptions.startTimeUs == C.TIME_UNSET || startTimeUs >= outputOptions.startTimeUs) {
output.accept(
new CuesWithTiming(
ImmutableList.of(buildCue(text, alignmentTag)),
startTimeUs,
/* durationUs= */ endTimeUs - startTimeUs));
} else if (cuesWithTimingBeforeRequestedStartTimeUs != null) {
cuesWithTimingBeforeRequestedStartTimeUs.add(
new CuesWithTiming(
ImmutableList.of(buildCue(text, alignmentTag)),
startTimeUs,
/* durationUs= */ endTimeUs - startTimeUs));
}
}
if (cuesWithTimingBeforeRequestedStartTimeUs != null) {
for (CuesWithTiming cuesWithTiming : cuesWithTimingBeforeRequestedStartTimeUs) {
output.accept(cuesWithTiming);
}
}
}
/**
* Determine UTF encoding of the byte array from a byte order mark (BOM), defaulting to UTF-8 if
* no BOM is found.
*/
private Charset detectUtfCharset(ParsableByteArray data) {
@Nullable Charset charset = data.readUtfCharsetFromBom();
return charset != null ? charset : Charsets.UTF_8;
}
/**
* Trims and removes tags from the given line. The removed tags are added to {@code tags}.
*
* @param line The line to process.
* @param tags A list to which removed tags will be added.
* @return The processed line.
*/
private String processLine(String line, ArrayList<String> tags) {
line = line.trim();
int removedCharacterCount = 0;
StringBuilder processedLine = new StringBuilder(line);
Matcher matcher = SUBRIP_TAG_PATTERN.matcher(line);
while (matcher.find()) {
String tag = matcher.group();
tags.add(tag);
int start = matcher.start() - removedCharacterCount;
int tagLength = tag.length();
processedLine.replace(start, /* end= */ start + tagLength, /* str= */ "");
removedCharacterCount += tagLength;
}
return processedLine.toString();
}
/**
* Build a {@link Cue} based on the given text and alignment tag.
*
* @param text The text.
* @param alignmentTag The alignment tag, or {@code null} if no alignment tag is available.
* @return Built cue
*/
private Cue buildCue(Spanned text, @Nullable String alignmentTag) {
Cue.Builder cue = new Cue.Builder().setText(text);
if (alignmentTag == null) {
return cue.build();
}
// Horizontal alignment.
switch (alignmentTag) {
case ALIGN_BOTTOM_LEFT:
case ALIGN_MID_LEFT:
case ALIGN_TOP_LEFT:
cue.setPositionAnchor(Cue.ANCHOR_TYPE_START);
break;
case ALIGN_BOTTOM_RIGHT:
case ALIGN_MID_RIGHT:
case ALIGN_TOP_RIGHT:
cue.setPositionAnchor(Cue.ANCHOR_TYPE_END);
break;
case ALIGN_BOTTOM_MID:
case ALIGN_MID_MID:
case ALIGN_TOP_MID:
default:
cue.setPositionAnchor(Cue.ANCHOR_TYPE_MIDDLE);
break;
}
// Vertical alignment.
switch (alignmentTag) {
case ALIGN_BOTTOM_LEFT:
case ALIGN_BOTTOM_MID:
case ALIGN_BOTTOM_RIGHT:
cue.setLineAnchor(Cue.ANCHOR_TYPE_END);
break;
case ALIGN_TOP_LEFT:
case ALIGN_TOP_MID:
case ALIGN_TOP_RIGHT:
cue.setLineAnchor(Cue.ANCHOR_TYPE_START);
break;
case ALIGN_MID_LEFT:
case ALIGN_MID_MID:
case ALIGN_MID_RIGHT:
default:
cue.setLineAnchor(Cue.ANCHOR_TYPE_MIDDLE);
break;
}
return cue.setPosition(getFractionalPositionForAnchorType(cue.getPositionAnchor()))
.setLine(getFractionalPositionForAnchorType(cue.getLineAnchor()), Cue.LINE_TYPE_FRACTION)
.build();
}
private static long parseTimecode(Matcher matcher, int groupOffset) {
@Nullable String hours = matcher.group(groupOffset + 1);
long timestampMs = hours != null ? Long.parseLong(hours) * 60 * 60 * 1000 : 0;
timestampMs +=
Long.parseLong(Assertions.checkNotNull(matcher.group(groupOffset + 2))) * 60 * 1000;
timestampMs += Long.parseLong(Assertions.checkNotNull(matcher.group(groupOffset + 3))) * 1000;
@Nullable String millis = matcher.group(groupOffset + 4);
if (millis != null) {
timestampMs += Long.parseLong(millis);
}
return timestampMs * 1000;
}
// TODO(b/289983417): Make package-private again, once it is no longer needed in
// DelegatingSubtitleDecoderWithSubripParserTest.java (i.e. legacy subtitle flow is removed)
@VisibleForTesting(otherwise = PRIVATE)
public static float getFractionalPositionForAnchorType(@Cue.AnchorType int anchorType) {
switch (anchorType) {
case Cue.ANCHOR_TYPE_START:
return START_FRACTION;
case Cue.ANCHOR_TYPE_MIDDLE:
return MID_FRACTION;
case Cue.ANCHOR_TYPE_END:
return END_FRACTION;
case Cue.TYPE_UNSET:
default:
// Should never happen.
throw new IllegalArgumentException();
}
}
}