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SReview::Video(3pm) User Contributed Perl Documentation SReview::Video(3pm)

NAME

SReview::Video - SReview internal representation of an asset

SYNOPSIS

  use SReview::Video;
  use SReview::Video::ProfileFactory;
  use SReview::Videopipe;
  # convert any input file to VP9 at recommended settings for vertical resolution and frame rate
  my $input = SReview::Video->new(url => $input_filename);
  my $profile = SReview::Video::ProfileFactory->new("vp9", $input);
  my $output = SReview::Video->new(url => $output_filename, reference => $profile);
  SReview::Videopipe->new(inputs => [$input], output => $output)->run();
  # do that again; but this time, force vorbis audio:
  $output = SReview::Video->new(url => $other_filename, reference => $profile);
  $output->audio_codec("libvorbis");
  SReview::Videopipe->new(inputs => [$input], output => $output)->run();

DESCRIPTION

The SReview::Video package is used to represent media assets inside SReview. It is a "Moose"-based base class for much of the other Video* classes in SReview.

There is one required attribute, "url", which represents the filename of the video (however, for SReview::Video::NGinX, it should be an HTTP URL instead).

If the "url" attribute points to an existing file and an attempt is made to read any of the codec, framerate, bit rate, or similar attributes (without explicitly writing to them first), then "SReview::Video" will call "ffprobe" on the file in question, and use that to populate the requested attributes. If it does not, or "ffprobe" is incapable of detecting the requested attribute (which may be the case for things like audio or video bitrate), then the attribute in question will resolve to "undef".

If the "url" attribute does not point to an existing file and an attempt is made to read any of the codec, framerate, bit rate, or similar attributes (without explicitly writing to them first), then they will resolve to "undef". However, if the "reference" attribute is populated with another "SReview::Video" object, then reading any of the codec, framerate, bit rate, or similar attributes (without explicitly writing to them first) will resolve to the value of the requested attribute that is set or detected on the "reference" object.

The return value of "SReview::Video::ProfileFactory->create()" is also an SReview::Video object, but with different implementations of some of the probing methods; this allows it to choose the correct values for things like bitrate and encoder speed based on properties set in the input object provided to the "SReview::Video::ProfileFactory->create()" method.

For more information on how to use the files referred to in the "SReview::Video" object in an ffmpeg command line, please see "SReview::Videopipe".

ATTRIBUTES

The following attributes are supported by SReview::Video. All attributes will be probed from ffprobe output unless noted otherwise.

url

The filename of the asset this object should deal with. Required at construction time. Will not be probed.

mtime

The mtime of the file backing this asset. Only defined if the file exists at the time the attribute is first read, and is not updated later on.

duration

The duration of this asset.

duration_style

The time unit is used for the "duration" attribute. One of 'seconds' (default) or 'frames'. Will not be probed.

video_codec

The codec in use for the video stream. Note that "ffprobe" will sometimes use a string (e.g., "vp8") that is not the best choice when instructing "ffmpeg" to transcode video to the said codec (for vp8, the use of "libvpx" is recommended). "SReview::CodecMap" is used to map detected codecs to output codecs and resolve this issue.

audio_codec

The codec in use for the audio stream. Note that "ffprobe" will sometimes use a string (e.g., "vorbis") that is not the best choice when instructing "ffmpeg" to transcode audio to the said codec (for vorbis, the use of "libvorbis" is recommended). "SReview::CodecMap" is used to map detected codecs to output codecs and resolve this issue.

video_size

A string representing the resolution of the video in "WxH" format, where W is the width and H is the height.

This attribute is special in that in contrast to all the other attributes, it is not provided directly by "ffprobe"; instead, when this parameter is read, the "video_width" and "video_height" attributes are read and combined.

That does mean that you should not read this attribute, and based on that possibly set the height and/or width attributes of a video (or vice versa). Instead, you should read either the "video_width" and "video_height" attribute, or this one.

Failure to follow this rule will result in undefined behaviour.

video_width

The width of the video, in pixels.

video_height

The height of the video, in pixels.

video_bitrate

The bit rate of this video, in bits per second.

Note that not all container formats support probing the bitrate of the encoded video or audio; when read on input objects with those that do not, this will resolve to "undef".

video_minrate

The minimum bit rate for this video, in bits per second.

Defaults to 0.5 * video_bitrate

video_maxrate

The maximum bit rate for this video, in bits per second.

Defaults to 1.45 * video_bitrate

aspect_ratio

The Display Aspect Ratio of a video. Note that with non-square pixels, this is not guaranteed to be what one would expect when reading the "video_size" attribute.

audio_bitrate

The bit rate of the audio stream on this video, in bits per second

audio_samplerate

The sample rate of the audio, in samples per second

video_framerate

The frame rate of the video, as a fraction.

Note that in the weird US frame rate, this could be 30000/1001.

fragment_start

If set, this instructs SReview on read to only read a particular part of the video from this file. Should be specified in seconds; will not be probed.

quality

The quality used for the video encoding, i.e., the value passed to the "-crf" parameter. Mostly for use by a profile. Will not be probed.

metadata

Can be used to set video metadata (as per "ffmpeg"'s "-metadata" parameter). Functions "add_metadata" and "drop_metadata" can be used to add or remove individual metedata values. Will not be probed.

reference

If set to any "SReview::Video" object, then when any value is being probed, rather than trying to run "ffprobe" on the file pointed to by our "url" attribute, we will use the value reported by the referenced object.

Can be used in "build a file almost like this one, but with these things different" kind of scenarios.

Will not be probed (obviously).

pix_fmt

The pixel format (e.g., "yuv420p" or the likes) of the video.

astream_id

Returns the numeric ID for the first audio stream in this file. Useful for the implementation of stream mappings etc; see "SReview::Map"

blackspots

Returns an array of hashes. Each hash contains a member "start", "end", and "duration", containing the start, end, and duration, respectively, of locations in the video file that are (almost) entirely black.

Could be used by a script for automatic review.

Note that the ffmpeg run required to detect blackness is CPU intensive and may require a very long time to finish.

astream_ids

Returns an array with the IDs for the audio streams in this file.

astream_count

Returns the number of audio streams in this file.

vstream_id

Returns the numeric ID for the first video stream in this file. Useful for the implementation of stream mappings etc; see "SReview::Map"

extra_params

Add extra parameters. This should be used sparingly, rather add some abstraction.

time_offset

Apply an input time offset to this video (only valid when used as an input video in SReview::Videopipe). Can be used to apply A/V sync correction values.

2022-10-15 perl v5.34.0