jellyfin/jellyfin · error · ResourceNotFoundException

Attachment with stream index {attachmentStreamIndex} can't b

Error message

Attachment with stream index {attachmentStreamIndex} can't be extracted for MediaSource {mediaSourceId}

What it means

An intentional extraction refusal: the matched attachment's Codec is 'mjpeg' (case-insensitive). MJPEG 'attachments' are embedded cover/cover-image frames, not the font files attachment extraction is built for, so ffmpeg cannot pull them out as a normal attachment. Treated as ResourceNotFoundException (404) so clients treat it as 'not extractable'.

Source

Thrown at MediaBrowser.MediaEncoding/Attachments/AttachmentExtractor.cs:89

            var mediaSources = await _mediaSourceManager.GetPlaybackMediaSources(item, null, true, false, cancellationToken).ConfigureAwait(false);
            var mediaSource = mediaSources
                .FirstOrDefault(i => string.Equals(i.Id, mediaSourceId, StringComparison.OrdinalIgnoreCase));
            if (mediaSource is null)
            {
                throw new ResourceNotFoundException($"MediaSource {mediaSourceId} not found");
            }

            var mediaAttachment = mediaSource.MediaAttachments
                .FirstOrDefault(i => i.Index == attachmentStreamIndex);
            if (mediaAttachment is null)
            {
                throw new ResourceNotFoundException($"MediaSource {mediaSourceId} has no attachment with stream index {attachmentStreamIndex}");
            }

            if (string.Equals(mediaAttachment.Codec, "mjpeg", StringComparison.OrdinalIgnoreCase))
            {
                throw new ResourceNotFoundException($"Attachment with stream index {attachmentStreamIndex} can't be extracted for MediaSource {mediaSourceId}");
            }

            var attachmentStream = await GetAttachmentStream(mediaSource, mediaAttachment, cancellationToken)
                    .ConfigureAwait(false);

            return (mediaAttachment, attachmentStream);
        }

        /// <inheritdoc />
        public async Task ExtractAllAttachments(
            string inputFile,
            MediaSourceInfo mediaSource,
            CancellationToken cancellationToken)
        {
            var shouldExtractOneByOne = mediaSource.MediaAttachments.Any(a => !string.IsNullOrEmpty(a.FileName)
                                                                              && !string.Equals(PathHelper.GetSafeLeafFileName(a.FileName), a.FileName, StringComparison.Ordinal));
            if (shouldExtractOneByOne && !inputFile.EndsWith(".mks", StringComparison.OrdinalIgnoreCase))
            {

View on GitHub (pinned to ae8723026d)

Solutions

Skip attachments whose codec is mjpeg when listing extractable attachments.
Use the cover-art/image endpoint instead of the attachment endpoint for embedded MJPEG art.
Filter client-side before issuing the extraction request.

Example fix

// before
var attachment = mediaSource.MediaAttachments.First(a => a.Index == idx);

// after: skip non-extractable MJPEG art
var attachment = mediaSource.MediaAttachments
    .FirstOrDefault(a => a.Index == idx
        && !string.Equals(a.Codec, "mjpeg", StringComparison.OrdinalIgnoreCase));

Defensive patterns

Strategy: validation

Validate before calling

// Skip MJPEG attachments (embedded cover art) before extracting.
if (string.Equals(attach.Codec, "mjpeg", StringComparison.OrdinalIgnoreCase))
{
    return NotFound("MJPEG attachments are not extractable; use the cover-art endpoint.");
}

Type guard

static bool IsExtractableAttachment(MediaAttachment a) =>
    !string.Equals(a.Codec, "mjpeg", StringComparison.OrdinalIgnoreCase);

Try / catch

try { /* extract */ }
catch (ResourceNotFoundException ex) when (ex.Message.Contains("can't be extracted"))
{
    return NotFound("Attachment is MJPEG cover art and cannot be extracted.");
}

Prevention

Filter MJPEG attachments out of any 'extract all attachments' loop.
Use the image/cover-art endpoint for embedded MJPEG art.
Document that MJPEG attachments are intentionally non-extractable.

When it happens

Trigger: mediaAttachment is found and string.Equals(mediaAttachment.Codec, "mjpeg", StringComparison.OrdinalIgnoreCase) is true.

Common situations: A media file stores its cover art as an MJPEG attachment; the client blindly tries to extract every listed attachment; metadata reports an attachment whose codec is mjpeg.

Related errors

AI-assisted analysis of jellyfin/jellyfin@ae8723026d (2026-08-13). Data as JSON: /api/errors/295b5341a5b52e1f. Report an issue: GitHub.