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Optimize cache preview generation with fast FFmpeg seeks. #505

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Optimize cache preview generation with fast FFmpeg seeks. #505

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42 changes: 28 additions & 14 deletions backend/src/main/kotlin/dev/dres/mgmt/cache/CacheManager.kt
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Original file line number Diff line number Diff line change
Expand Up @@ -21,6 +21,7 @@ import org.slf4j.LoggerFactory
import org.slf4j.MarkerFactory
import java.awt.Image
import java.awt.image.BufferedImage
import java.io.IOException
import java.nio.file.Files
import java.nio.file.Path
import java.nio.file.StandardOpenOption
Expand Down Expand Up @@ -355,18 +356,25 @@ class CacheManager(private val config: Config, private val store: TransientEntit
*/
inner class PreviewImageFromVideoRequest constructor(input: Path, output: Path, private val start: Long, private val size: Int = this@CacheManager.config.cache.previewImageMaxSize): AbstractPreviewRequest(input, output) {
override fun call(): Path = try {
FFmpeg.atPath(this@CacheManager.ffmpegBin).
addInput(UrlInput.fromPath(this.input))
FFmpeg.atPath(this@CacheManager.ffmpegBin)
.addArguments("-ss", millisecondToTimestamp(this.start)) // Seek before decoding for fast access.
.addInput(UrlInput.fromPath(this.input))
.addOutput(UrlOutput.toPath(this.output))
.setOverwriteOutput(true)
.addArguments("-ss", millisecondToTimestamp(this.start))
.addArguments("-filter:v", "scale=${this.size}:-1")
.addArguments("-frames:v", "1")
.addArguments("-filter:v", "scale=${this@CacheManager.config.cache.previewImageMaxSize}:-1")
.setOutputListener { l -> LOGGER.debug(MARKER, l); }
.execute()

if (Files.notExists(this.output) || Files.size(this.output) == 0L) {
Files.deleteIfExists(this.output)
throw IOException("FFmpeg failed to produce a valid output file: ${this.output}")
}

this.output
} catch (e: Exception) {
LOGGER.error("Error in FFMpeg: ${e.message}")
LOGGER.error("Error in FFMpeg: ${e.message}", e)
Files.deleteIfExists(this.output)
throw e
} finally {
this@CacheManager.inTransit.remove(this.output) /* Remove this PreviewImageFromVideoRequest. */
Expand All @@ -380,24 +388,30 @@ class CacheManager(private val config: Config, private val store: TransientEntit
override fun call(): Path = try {
val startTimecode = millisecondToTimestamp(this.start)
val endTimecode = millisecondToTimestamp(this.end)
val duration = this.end - this.start
val durationTimecode = millisecondToTimestamp(duration)

LOGGER.info(MARKER, "Start rendering segment for video $input from $startTimecode to $endTimecode")
FFmpeg.atPath(this@CacheManager.ffmpegBin)
.addArguments("-ss", startTimecode) // Fast seek before decoding for quick segment extraction.
.addInput(UrlInput.fromPath(this.input))
.addOutput(UrlOutput.toPath(this.output))
.setOverwriteOutput(true)
.addArguments("-ss", startTimecode)
.addArguments("-to", endTimecode)
.addArguments("-c:v", "libx264")
.addArguments("-c:a", "aac")
.addArguments("-b:v", "2000k")
.addArguments("-filter:v", "scale=${this@CacheManager.config.cache.previewVideoMaxSize}:-1")
.addArguments("-tune", "zerolatency")
.addArguments("-preset", "slow")
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@lucaro lucaro Dec 12, 2025

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This re-encoding is very deliberate to improve reliability when playing back the target sequences in the viewer. What was your reasoning to change this?

.addArguments("-t", durationTimecode)
.addArguments("-c:v", "copy")
.addArguments("-c:a", "copy")
.setOutputListener { l -> LOGGER.debug(MARKER, l); }
.execute()

if (Files.notExists(this.output) || Files.size(this.output) == 0L) {
Files.deleteIfExists(this.output)
throw IOException("FFmpeg failed to produce a valid preview video: ${this.output}")
}

this.output
} catch (e: Exception) {
LOGGER.error("Error in FFMpeg: ${e.message}")
LOGGER.error("Error in FFMpeg: ${e.message}", e)
Files.deleteIfExists(this.output)
throw e
} finally {
this@CacheManager.inTransit.remove(this.output) /* Remove this PreviewImageFromVideoRequest. */
Expand Down