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google#4306 - Extract tags from SubRip subtitles, add support for ali…
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…gnment tags based on SSA v4+
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@szaboa
szaboa committed Jul 24, 2018
1 parent 05a31df commit ae520a8
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201 changes: 199 additions & 2 deletions library/core/src/main/java/com/google/android/exoplayer2/text/subrip/SubripDecoder.java
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Original file line number Diff line number Diff line change
Expand Up @@ -15,15 +15,21 @@
*/
package com.google.android.exoplayer2.text.subrip;

import android.support.annotation.StringDef;
import android.text.Html;
import android.text.Layout;
import android.text.Spanned;
import android.text.TextUtils;
import android.util.Log;
import com.google.android.exoplayer2.text.Cue;
import com.google.android.exoplayer2.text.SimpleSubtitleDecoder;
import com.google.android.exoplayer2.util.LongArray;
import com.google.android.exoplayer2.util.ParsableByteArray;

import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.util.ArrayList;
import java.util.List;
import java.util.regex.Matcher;
import java.util.regex.Pattern;

Expand All @@ -38,6 +44,33 @@ public final class SubripDecoder extends SimpleSubtitleDecoder {
private static final Pattern SUBRIP_TIMING_LINE =
Pattern.compile("\\s*(" + SUBRIP_TIMECODE + ")\\s*-->\\s*(" + SUBRIP_TIMECODE + ")?\\s*");

private static final Pattern SUBRIP_TAG_PATTERN = Pattern.compile("\\{\\\\.*?\\}");
private static final String SUBRIP_ALIGNMENT_TAG = "\\{\\\\an[1-9]\\}";

private static final float DEFAULT_START_FRACTION = 0.08f;
private static final float DEFAULT_END_FRACTION = 1 - DEFAULT_START_FRACTION;
private static final float DEFAULT_MID_FRACTION = 0.5f;

@Retention(RetentionPolicy.SOURCE)
@StringDef({
ALIGN_BOTTOM_LEFT, ALIGN_BOTTOM_MID, ALIGN_BOTTOM_RIGHT,
ALIGN_MID_LEFT, ALIGN_MID_MID, ALIGN_MID_RIGHT,
ALIGN_TOP_LEFT, ALIGN_TOP_MID, ALIGN_TOP_RIGHT
})

private @interface SubRipTag {}

// Possible valid alignment tags based on SSA v4+ specs
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;

public SubripDecoder() {
Expand Down Expand Up @@ -95,8 +128,36 @@ protected SubripSubtitle decode(byte[] bytes, int length, boolean reset) {
textBuilder.append(currentLine.trim());
}

Spanned text = Html.fromHtml(textBuilder.toString());
cues.add(new Cue(text));
// Extract tags
SubtitleTagResult tagResult = extractTags(textBuilder);
Spanned text = Html.fromHtml(tagResult.cue);

Cue cue = null;

// Check if tags are present
if (tagResult.tags.length > 0) {

boolean alignTagFound = false;

// At end of this loop the clue must be created with the applied tags
for (String tag : tagResult.tags) {

// Check if the tag is an alignment tag
if (tag.matches(SUBRIP_ALIGNMENT_TAG)) {

// Based on the specs, in case of the alignment tags only the first appearance counts
if (alignTagFound) continue;
alignTagFound = true;

AlignmentResult alignmentResult = getAlignmentValues(tag);
cue = new Cue(text, Layout.Alignment.ALIGN_NORMAL, alignmentResult.line, Cue.LINE_TYPE_FRACTION,
alignmentResult.lineAnchor, alignmentResult.position, alignmentResult.positionAnchor, Cue.DIMEN_UNSET);
}
}
}

cues.add(cue == null ? new Cue(text) : cue);

if (haveEndTimecode) {
cues.add(null);
}
Expand All @@ -108,6 +169,111 @@ protected SubripSubtitle decode(byte[] bytes, int length, boolean reset) {
return new SubripSubtitle(cuesArray, cueTimesUsArray);
}

/**
* Extracts the tags from the given {@code cue}
* The pattern that is used to extract the tags is specified in SSA v4+ specs and
* has the following form: "{\...}".
* <p>
* "All override codes appear within braces {}"
* "All override codes are always preceded by a backslash \"
*
* @param cue Cue text
* @return {@link SubtitleTagResult} that holds new cue and also the extracted tags
*/
private SubtitleTagResult extractTags(StringBuilder cue) {
StringBuilder cueCopy = new StringBuilder(cue.toString());
List<String> tags = new ArrayList<>();

int replacedCharacters = 0;

Matcher matcher = SUBRIP_TAG_PATTERN.matcher(cue.toString());
while (matcher.find()) {
String tag = matcher.group();
tags.add(tag);
cueCopy.replace(matcher.start() - replacedCharacters, matcher.end() - replacedCharacters, "");
replacedCharacters += tag.length();
}

return new SubtitleTagResult(tags.toArray(new String[tags.size()]), cueCopy.toString());
}

/**
* Match the alignment tag and calculate the line, position, position anchor accordingly
*
* Based on SSA v4+ specs the alignment tag can have the following form: {\an[1-9},
* where the number specifies the direction (based on the numpad layout).
* Note. older SSA scripts may contain tags like {\a1[1-9]} but these are based on
* other direction rules, but multiple sources says that these are deprecated, so no support here either
*
* @param tag Alignment tag
* @return {@link AlignmentResult} that holds the line, position, position anchor values
*/
private AlignmentResult getAlignmentValues(String tag) {
// Default values used for positioning the subtitle in case of align tags
float line = DEFAULT_END_FRACTION, position = DEFAULT_MID_FRACTION;
@Cue.AnchorType int positionAnchor = Cue.ANCHOR_TYPE_MIDDLE;
@Cue.AnchorType int lineAnchor = Cue.ANCHOR_TYPE_END;

switch (tag) {
case ALIGN_BOTTOM_LEFT:
line = DEFAULT_END_FRACTION;
position = DEFAULT_START_FRACTION;
positionAnchor = Cue.ANCHOR_TYPE_START;
lineAnchor = Cue.ANCHOR_TYPE_END;
break;
case ALIGN_BOTTOM_MID:
line = DEFAULT_END_FRACTION;
position = DEFAULT_MID_FRACTION;
positionAnchor = Cue.ANCHOR_TYPE_MIDDLE;
lineAnchor = Cue.ANCHOR_TYPE_END;
break;
case ALIGN_BOTTOM_RIGHT:
line = DEFAULT_END_FRACTION;
position = DEFAULT_END_FRACTION;
positionAnchor = Cue.ANCHOR_TYPE_END;
lineAnchor = Cue.ANCHOR_TYPE_END;
break;
case ALIGN_MID_LEFT:
line = DEFAULT_MID_FRACTION;
position = DEFAULT_START_FRACTION;
positionAnchor = Cue.ANCHOR_TYPE_START;
lineAnchor = Cue.ANCHOR_TYPE_MIDDLE;
break;
case ALIGN_MID_MID:
line = DEFAULT_MID_FRACTION;
position = DEFAULT_MID_FRACTION;
positionAnchor = Cue.ANCHOR_TYPE_MIDDLE;
lineAnchor = Cue.ANCHOR_TYPE_MIDDLE;
break;
case ALIGN_MID_RIGHT:
line = DEFAULT_MID_FRACTION;
position = DEFAULT_END_FRACTION;
positionAnchor = Cue.ANCHOR_TYPE_END;
lineAnchor = Cue.ANCHOR_TYPE_MIDDLE;
break;
case ALIGN_TOP_LEFT:
line = DEFAULT_START_FRACTION;
position = DEFAULT_START_FRACTION;
positionAnchor = Cue.ANCHOR_TYPE_START;
lineAnchor = Cue.ANCHOR_TYPE_START;
break;
case ALIGN_TOP_MID:
line = DEFAULT_START_FRACTION;
position = DEFAULT_MID_FRACTION;
positionAnchor = Cue.ANCHOR_TYPE_MIDDLE;
lineAnchor = Cue.ANCHOR_TYPE_START;
break;
case ALIGN_TOP_RIGHT:
line = DEFAULT_START_FRACTION;
position = DEFAULT_END_FRACTION;
positionAnchor = Cue.ANCHOR_TYPE_END;
lineAnchor = Cue.ANCHOR_TYPE_START;
break;
}

return new AlignmentResult(positionAnchor, position, lineAnchor, line);
}

private static long parseTimecode(Matcher matcher, int groupOffset) {
long timestampMs = Long.parseLong(matcher.group(groupOffset + 1)) * 60 * 60 * 1000;
timestampMs += Long.parseLong(matcher.group(groupOffset + 2)) * 60 * 1000;
Expand All @@ -116,4 +282,35 @@ private static long parseTimecode(Matcher matcher, int groupOffset) {
return timestampMs * 1000;
}

/**
* Class that holds the tags, new clue after the tag extraction
*/
private static final class SubtitleTagResult {
public final String[] tags;
public final String cue;

public SubtitleTagResult(String[] tags, String cue) {
this.tags = tags;
this.cue = cue;
}
}

/**
* Class that holds the parsed and mapped alignment values (such as line,
* position and anchor type of line)
*/
private static final class AlignmentResult {

public @Cue.AnchorType int positionAnchor;
public @Cue.AnchorType int lineAnchor;
public float position, line;

public AlignmentResult(@Cue.AnchorType int positionAnchor, float position, @Cue.AnchorType int lineAnchor, float line) {
this.positionAnchor = positionAnchor;
this.position = position;
this.line = line;
this.lineAnchor = lineAnchor;
}
}

}
20 changes: 20 additions & 0 deletions library/core/src/test/assets/subrip/typical_with_tags
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Original file line number Diff line number Diff line change
@@ -0,0 +1,20 @@
1
00:00:00,000 --> 00:00:01,234
This is {\an1} the first subtitle.

2
00:00:02,345 --> 00:00:03,456
This is the second subtitle.
Second {\ an 2} subtitle with second line.

3
00:00:04,567 --> 00:00:08,901
This {\an2} is the third {\ tag} subtitle.

4
00:00:09,567 --> 00:00:12,901
This { \an2} is the fourth subtitle.

5
00:00:013,567 --> 00:00:14,901
This {\an2} is the fifth subtitle with multiple {\xyz} valid {\qwe} tags.
22 changes: 22 additions & 0 deletions library/core/src/test/java/com/google/android/exoplayer2/text/subrip/SubripDecoderTest.java
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Original file line number Diff line number Diff line change
Expand Up @@ -36,6 +36,7 @@ public final class SubripDecoderTest {
private static final String TYPICAL_MISSING_SEQUENCE = "subrip/typical_missing_sequence";
private static final String TYPICAL_NEGATIVE_TIMESTAMPS = "subrip/typical_negative_timestamps";
private static final String TYPICAL_UNEXPECTED_END = "subrip/typical_unexpected_end";
private static final String TYPICAL_WITH_TAGS = "subrip/typical_with_tags";
private static final String NO_END_TIMECODES_FILE = "subrip/no_end_timecodes";

@Test
Expand Down Expand Up @@ -154,6 +155,27 @@ public void testDecodeNoEndTimecodes() throws IOException {
.isEqualTo("Or to the end of the media.");
}

@Test
public void testDecodeCueWithTag() throws IOException{
SubripDecoder decoder = new SubripDecoder();
byte[] bytes = TestUtil.getByteArray(RuntimeEnvironment.application, TYPICAL_WITH_TAGS);
SubripSubtitle subtitle = decoder.decode(bytes, bytes.length, false);
assertThat(subtitle.getCues(subtitle.getEventTime(0)).get(0).text.toString())
.isEqualTo("This is the first subtitle.");
assertThat(subtitle.getCues(subtitle.getEventTime(2)).get(0).text.toString())
.isEqualTo("This is the second subtitle.\nSecond subtitle with second line.");
assertThat(subtitle.getCues(subtitle.getEventTime(4)).get(0).text.toString())
.isEqualTo("This is the third subtitle.");

// Based on the SSA v4+ specs the curly bracket must be followed by a backslash, so this is
// not a valid tag (won't be parsed / replaced)
assertThat(subtitle.getCues(subtitle.getEventTime(6)).get(0).text.toString())
.isEqualTo("This { \\an2} is the fourth subtitle.");

assertThat(subtitle.getCues(subtitle.getEventTime(8)).get(0).text.toString())
.isEqualTo("This is the fifth subtitle with multiple valid tags.");
}

private static void assertTypicalCue1(SubripSubtitle subtitle, int eventIndex) {
assertThat(subtitle.getEventTime(eventIndex)).isEqualTo(0);
assertThat(subtitle.getCues(subtitle.getEventTime(eventIndex)).get(0).text.toString())
Expand Down

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