Fix temp files generated during the upload process not being cleaned up quickly enough. This included
downloaded files, generated preview images, and Ugoira video conversions.
Before we relied on `Tempfile` cleaning up files automatically. But this only happened when the
Tempfile object was garbage collected, which could take a long time. In the meantime we could have
hundreds of megabytes of temp files hanging around.
The fix is to explicitly close temp files when we're done with them. But the standard `Tempfile`
class doesn't immediately delete the file when it's closed. So we also have to introduce a
Danbooru::Tempfile wrapper that deletes the tempfile as soon as it's closed.
For videos with sound, save information about audio volume levels in the
media asset's metadata. These values are stored:
* FFmpeg:AudioPeakLoudness The peak loudness of the audio track, from 0.0 (silent) to 1.0 (max volume)
* FFmpeg:AudioAverageLoudness The average loudness of the audio track, from 0.0 (silent) to 1.0 (max volume).
* FFmpeg:AudioLoudnessRange The difference between the quietest and loudest sounds in the audio track (in decibels).
* FFmpeg:AudioSilencePercentage The percentage of the video that is silent (1.0 is completely silent, 0.5 is 50% silence, 0.0 is no silence).
These values are calculated based on the EBU R 128 standard, using the ffmpeg command below:
ffmpeg -i file.mp4 -af silencedetect=duration=0.05:noise=0.0001,ebur128=metadata=1:peak=true:dualmono=true -f null /dev/null
See the links below for details:
* https://en.wikipedia.org/wiki/EBU_R_128
* https://www.ffmpeg.org/ffmpeg-filters.html#ebur128-1
* https://tech.ebu.ch/loudness
* https://tech.ebu.ch/docs/tech/tech3341.pdf
Fix .webm files not including the `FFmpeg:VideoBitRate` and `FFmpeg:AudioBitRate`
fields in the media_metadata table. This was because the .webm format
doesn't include the video or audio bit rates in the metadata, and
ffprobe doesn't calculate them either, so we have to calculate them
ourselves by hand.
Fixup for 523d7afdd.
Include the following metadata tags for videos:
* FFmpeg:MajorBrand (e.g. mp42)
* FFmpeg:PixFmt (e.g. yuv420p. Indicates bit depth and color subsampling mode)
* FFmpeg:FrameCount (e.g. total number of frames in the video)
* FFmpeg:VideoCodec (e.g. h264)
* FFmpeg:VideoProfile (e.g. Main)
* FFmpeg:AudioCodec (e.g. AAC)
* FFmpeg:AudioProfile (e.g. LC)
* FFmpeg:AudioLayout (e.g. stereo)
* FFmpeg:AudioBitRate (e.g. 128kb/s)
If a media asset is corrupt, include the error message from libvips or
ffmpeg in the "Vips:Error" or "FFmpeg:Error" fields in the media
metadata table.
Corrupt files can't be uploaded nowadays, but they could be in the past,
so we have some old corrupted files that we can't generate thumbnails
for. This lets us mark these files in the metadata so they're findable
with the tag search `exif:Vips:Error`.
Known bug: Vips has a single global error buffer that is shared between
threads and that isn't cleared between operations. So we can't reliably
get the actual error message because it may pick up errors from other
threads, or from previous operations in the same thread.
Don't allow uploading videos with unsupported video codecs.
The only video codecs we allow for MP4 files are H.264 and VP9. Other
codecs, including H.265 (aka HEVC), MPEG-4 part 2, and AV1, are
disallowed because they're not universally supported by browsers.
Firefox doesn't support H.265 or MPEG-4 part 2, and Safari doesn't
support AV1.
Additionally, don't allow videos with multiple video tracks, multiple
audio tracks, or no video tracks. Multiple video and audio tracks are
disallowed because they're rare and for moderation purposes, we don't
want people hiding content in extra tracks.
These restrictions really only apply to MP4 videos, since WebM files
don't support multiple video or audio tracks and only support a limited
number of codecs (VP8 and VP9 for videos, Vorbis and Opus for audio).
There are currently 22 posts with unsupported video codecs:
* https://danbooru.donmai.us/posts?tags=video+is:mp4+-exif:Track1:CompressorID=avc1+-exif:Track2:CompressorID=avc1+-exif:Track1:CompressorID=vp09+-exif:Track2:CompressorID=vp09 # AVC1 is H.264
There is one post that has multiple audio tracks:
* https://danbooru.donmai.us/posts/2382057
Fix StatementInvalid exception when uploading https://files.catbox.moe/vxoe2p.mp4.
This was a result of multiple bugs:
* First, generating thumbnails for the video failed. This was because
the video uses the AV1 codec, which FFmpeg failed to decode. It failed
because our version of FFmpeg was built without the `--enable-libdav1d`
flag, so it uses the builtin AV1 decoder, which apparently can't
handle this particular video (it spews a bunch of errors about "Failed
to get pixel format" and "missing sequence header" and "failed to get
reference frame").
* Because generating the thumbnails failed, an exception was raised. We
tried to save the error message in the upload_media_assets.error
field. However, this also failed because the error message was 77kb
long (it contained the entire output of the ffmpeg command), but the
`upload_media_assets` table had a btree index on the `error` column,
which meant the maximum length of the error column was limited to
~2.7kb. This lead to a StatementInvalid exception being raised.
* Because the StatementInvalid exception was raised while we were trying
to set the upload media asset's status to `failed`, the upload was
left stuck in the `processing` state rather than being set to the
`failed` state.
* Because the upload was stuck in the `processing` state, the upload
page would hang forever waiting for the upload to complete.
The fixes are to:
* Build FFmpeg with `--enable-libdav1d` to use libdav1d for decoding AV1
videos instead of the builtin AV1 decoder.
* Remove the index on the `upload_media_assets.error` column so that
setting overly long error messages won't fail.
* Catch unexpected exceptions in ProcessUploadMediaAssetJob so we can
mark uploads as failed, even if `process_upload!` itself fails because
it raises an unexpected exception inside its own exception handler.
* Check that the video is playable with `MediaFile::Video#is_corrupt?` before
allowing it to be uploaded. This way we can return a better error
message if we can't generate thumbnails because the video isn't
playable. This requires decoding the entire video, so it means uploads
may take several seconds longer for long videos. It's also a security
risk in case ffmpeg has any bugs.
* Define `MediaAsset#preview!` as raising an exception on error, so
it's clear that generating thumbnails can fail. Define `MediaAsset#preview`
as returning nil on error for when we don't care about the cause of
the error.
Add methods to MediaFile to calculate the duration, frame count, and
frame rate of animated GIFs, PNGs, Ugoiras, and videos.
Some considerations:
* It's possible to have a GIF or PNG that's technically animated but
just has one frame. These are treated as non-animated images.
* It's possible to have an animated GIF that has an unspecified
frame rate. In this case we assume the frame rate is 10 FPS; this is
browser dependent and may not be correct.
* Animated GIFs, PNGs, and Ugoiras all support variable frame rates.
Technically, each frame has a separate delay, and the delays can be
different frame-to-frame. We report only the average frame rate.
* Getting the duration of an APNG is surprisingly hard. Most tools don't
have good support for APNGs since it's a rare and non-standardized
format. The best we can do is get the frame count using ExifTool and the
frame rate using ffprobe, then calculate the duration from that.
* Move image thumbnail generation code to MediaFile::Image.
* Move video thumbnail generation code to MediaFile::Video.
* Move ugoira->webm conversion code to MediaFile::Ugoira.
This separates thumbnail generation from the upload process so that it's
possible to generate thumbnails outside of uploads.
* Add MediaFile abstraction. A MediaFile represents an image or video file.
* Move filetype detection and dimension parsing code from uploads to MediaFile.
