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fix(streaming): hitches in VoDs & Clips resulting from ffmpeg concatenation (#44)
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- Resolves #43

Reviewed-on: #44
This commit was merged in pull request #44.
This commit is contained in:
Dylan De Faoite
2026-09-16 19:49:04 +01:00
parent 9758bb296b
commit d81202f905
6 changed files with 60 additions and 136 deletions
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2
src/main/java/com/ddf/vodsystem/services/MediaService.java
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@@ -239,7 +239,7 @@ public class MediaService {
onSuccess.run();
}).exceptionally(ex -> {
job.setState(JobState.FAILED);
job.setErrorOutput(ex.getMessage());
job.setErrorOutput("FFMPEG failed to save stream segments");
logger.error("Stream save job {} failed: {}", job.getUuid(), ex.getMessage());
return null;
});

114
src/main/java/com/ddf/vodsystem/services/media/StreamActionsService.java
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@@ -16,6 +16,7 @@ import java.util.Comparator;
import java.util.List;
import java.util.concurrent.CompletableFuture;
import java.util.concurrent.ExecutionException;
import java.util.stream.Collectors;
import java.util.stream.Stream;
/**
@@ -42,13 +43,14 @@ public class StreamActionsService {
* A resolved section of a stream, ready to be muxed by {@link #saveSection}.
*
* @param segments the segments to concatenate, in playback order; never empty
* @param trimOffset seconds to trim from the start of {@code segments.getFirst()}
* so playback begins at the requested moment, or {@code 0}
* when the first segment already starts there
* @param duration seconds of footage to keep, measured from the trim point.
* When the requested start fell in a recording gap and the
* leading segment was dropped, this is measured from the
* later real start so the section still ends where requested
* @param trimOffset seconds between the start of {@code segments.getFirst()} and
* the requested start, or {@code 0} when the first segment
* already starts there. Segments are copied whole, so this is
* lead-in the section carries before the requested moment, not
* footage that gets trimmed away
* @param duration seconds of footage to keep, measured from the start of
* {@code segments.getFirst()} so the section ends at the
* requested end time with the lead-in included
*/
public record SegmentSelection(List<Path> segments, float trimOffset, float duration) {}
@@ -78,8 +80,6 @@ public class StreamActionsService {
long firstMs = parseTimestampMs(segments.getFirst());
float trimOffset = Math.max(0f, (startTime.toEpochMilli() - firstMs) / 1000f);
// A first segment shorter than the trim offset means the requested start
// lands in a gap after it; drop it and begin at the next recorded footage.
if (trimOffset > 0 && probeDurationSeconds(segments.getFirst()) < trimOffset) {
segments.removeFirst();
if (segments.isEmpty()) {
@@ -89,18 +89,19 @@ public class StreamActionsService {
trimOffset = 0f;
}
// Measure duration from where playback actually begins so a dropped
// leading segment shortens the section rather than overrunning endTime.
long effectiveStartMs = firstMs + (long) (trimOffset * 1000);
float duration = (endTime.toEpochMilli() - effectiveStartMs) / 1000f;
float duration = (endTime.toEpochMilli() - firstMs) / 1000f;
return new SegmentSelection(segments, trimOffset, duration);
}
/**
* Muxes a {@link SegmentSelection} to {@code outputFile}, trimming the leading
* segment to {@code selection.trimOffset()} and keeping {@code selection.duration()}
* seconds of footage.
* Muxes a {@link SegmentSelection} to {@code outputFile}, keeping
* {@code selection.duration()} seconds of footage.
* <p>
* Segments are concatenated byte-wise through ffmpeg's {@code concat:} protocol,
* which preserves the continuous timestamps nginx writes across fragments. The
* leading segment is copied whole rather than trimmed, so playback begins up to
* {@code selection.trimOffset()} seconds before the requested moment.
* <p>
* Runs asynchronously; failures (process-launch errors, ffmpeg failures,
* interruption) complete the returned future exceptionally rather than being
@@ -131,37 +132,19 @@ public class StreamActionsService {
"trimOffset must be >= 0 and duration must be > 0 (got " + trimOffset + ", " + duration + ")"));
}
Path headFragment = null;
Path concatList = null;
try {
// Only the first segment is trimmed, so re-encode just that fragment and
// stream-copy the rest. A zero offset means the first segment already
// starts at the requested point, so re-encoding it would be wasted work.
List<Path> fragments;
if (trimOffset > 0) {
headFragment = Files.createTempFile("reencode-section-", ".ts");
encodeHead(segments.getFirst(), trimOffset, headFragment);
fragments = new ArrayList<>();
fragments.add(headFragment);
fragments.addAll(segments.subList(1, segments.size()));
} else {
fragments = segments;
}
// The concat demuxer (unlike the concat: byte protocol) rebases each
// fragment's timestamps to run continuously across the joins, absorbing
// the discontinuity between the PTS-0 head and the copied fragments.
concatList = writeConcatList(fragments);
String concatInput = "concat:" + segments.stream()
.map(p -> p.toAbsolutePath().toString())
.collect(Collectors.joining("|"));
List<String> command = List.of(
"ffmpeg",
"-y",
"-f", "concat",
"-safe", "0",
"-i", concatList.toAbsolutePath().toString(),
"-progress", "pipe:1",
"-i", concatInput,
"-t", String.valueOf(duration),
"-c", "copy",
"-avoid_negative_ts", "make_zero",
outputFile.toAbsolutePath().toString()
);
@@ -180,9 +163,6 @@ public class StreamActionsService {
} catch (RuntimeException e) {
logger.error("Failed to save section to '{}': {}", outputFile, e.toString());
return CompletableFuture.failedFuture(e);
} finally {
deleteTempQuietly(headFragment);
deleteTempQuietly(concatList);
}
}
@@ -257,52 +237,4 @@ public class StreamActionsService {
throw new IOException("Failed to probe segment duration: " + segment, e);
}
}
private void encodeHead(Path firstSegment, float trimOffset, Path head)
throws IOException, InterruptedException {
List<String> command = List.of(
"ffmpeg",
"-y",
"-i", firstSegment.toAbsolutePath().toString(),
"-ss", String.valueOf(trimOffset),
"-c:v", "libx264",
"-preset", "veryfast",
"-crf", "20",
"-pix_fmt", "yuv420p",
"-c:a", "aac",
"-b:a", "160k",
"-muxdelay", "0",
"-muxpreload", "0",
"-f", "mpegts",
head.toAbsolutePath().toString()
);
logger.debug("Re-encoding head fragment '{}' from {}s", firstSegment, trimOffset);
commandRunner.run(command, line -> { /* head pass is short; no progress reporting */ });
if (!Files.exists(head) || Files.size(head) == 0) {
throw new IOException("Head re-encode produced no output — trimOffset " + trimOffset
+ "s may exceed the duration of " + firstSegment);
}
}
private Path writeConcatList(List<Path> fragments) throws IOException {
Path listFile = Files.createTempFile("concat-list-", ".txt");
List<String> lines = fragments.stream()
.map(p -> "file '" + p.toAbsolutePath().toString().replace("'", "'\\''") + "'")
.toList();
Files.write(listFile, lines);
return listFile;
}
private void deleteTempQuietly(Path tempFile) {
if (tempFile != null) {
try {
Files.deleteIfExists(tempFile);
} catch (IOException e) {
logger.warn("Failed to delete temp file '{}': {}", tempFile, e.toString());
}
}
}
}

4
src/main/resources/application-local.properties
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@@ -3,4 +3,6 @@ spring.docker.compose.file=docker-compose.dev.yml
media.temp.inputs=./videos/inputs
media.temp.outputs=./videos/outputs
media.users=${MEDIA_DATA}
media.streams=${STREAM_DATA}
media.streams=${STREAM_DATA}
logging.level.com.ddf.vodsystem=DEBUG