NAME
Media::Convert::Asset - Media::Convert representation of a media asset
SYNOPSIS
use Media::Convert::Asset;
use Media::Convert::ProfileFactory;
use Media::Convert::Pipe;
# convert any input file to VP9 at recommended settings for vertical resolution and frame rate
my $input = Media::Convert::Asset->new(url => $input_filename);
my $profile = Media::Convert::ProfileFactory->new("vp9", $input);
my $output = Media::Convert::Asset->new(url => $output_filename, reference => $profile);
Media::Convert::Pipe->new(inputs => [$input], output => $output)->run();
# do that again; but this time, force vorbis audio:
$output = Media::Convert::Asset->new(url => $other_filename, reference => $profile);
$output->audio_codec("libvorbis");
Media::Convert::Pipe->new(inputs => [$input], output => $output)->run();
# Merge the video stream from one file with the audio stream from another,
# and convert to VP9
use Media::Convert::Map;
my $input_v = Media::Convert::Asset->new(url => $input_video_filename);
my $input_a = Media::Convert::Asset->new(url => $input_audio_filename);
$profile = Media::Convert::ProfileFactory->new("vp9", $input);
$output = Media::Convert::Asset->new(url => $merged_filename, reference => $profile);
my $map_v = Media::Convert::Map->new(input => $input_v, type => "stream", choice => "video");
my $map_a = Media::Convert::Map->new(input => $input_a, type => "stream", choice => "audio");
Media::Convert::Pipe->new(inputs => [$input_a, $input_v], map => [$map_a, $map_v], output => $output)->run();DESCRIPTION
The Media::Convert::Asset package is used to represent media assets inside Media::Convert. It is a Moose-based base class for much of the other classes in Media::Convert.
There is one required attribute, url, which represents the filename of the asset.
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 Media::Convert::Asset 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 Media::Convert::Asset 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 Media::Convert::ProfileFactory->create() is also a Media::Convert 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 Media::Convert::ProfileFactory->create() method.
For more information on how to use the files referred to in the Media::Convert::Asset object in an ffmpeg command line, please see Media::Convert::Pipe.
ATTRIBUTES
The following attributes are supported by Media::Convert::Asset. 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.
canonical_duration
Which value to take as the canonical duration while probing the duration of a media file.
Unfortunately, some versions of ffprobe have bugs in that they either read or write corrupt values for some parts of a media file. Sometimes the video stream length is correct but the container length is not, sometimes it is the other way around.
Since, given that, it is not possible to choose a source that will always work as the probed value for the duration attribute, this needs to be configurable in some way.
This option can take the following values:
- container
-
Uses the duration value that is parsed from the container file, rather than any particular stream. If the parsing of that value is not buggy, this is the right thing to do, and therefore this is also the default.
- video
-
Uses the duration value that is parsed from the first video stream.
- audio
-
Uses the duration value that is parsed from the first audio stream.
duration
The duration of this asset. See canonical_duration for details on how it is probed.
duration_frames
The number of frames in this asset.
duration_style
The time unit is used for the duration attribute. One of 'seconds' (default) or 'frames'. Will not be probed.
Deprecated; will be removed in a future release. Use duration_frames instead of setting this to a non-default value.
force_key_frames
Can be set to an expression that can be passed to ffmpeg's -force_key_frames parameter. 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). Media::Convert::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). Media::Convert::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
video_preset
The value for the -preset parameter. Used by some codecs, like av1 (and pretty critical there).
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 Media::Convert 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 Media::Convert::Asset 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 Media::Convert::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.
channel_layouts
Returns an array of audio channel layouts, as detected by ffprobe.
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.
audio_channel_count
Returns the number of channels in the first audio stream
vstream_id
Returns the numeric ID for the first video stream in this file. Useful for the implementation of stream mappings etc; see Media::Convert::Map
extra_params
Add extra (output) parameters. This should be used sparingly, rather add some abstraction.
handles
add_param (adds an extra parameter)
drop_param (delete a parameter)
input_params
Add extra input parameters. This should be used sparingly, rather add some abstraction.
handles
add_input_param (adds an extra parameter)
drop_input_param (delete a parameter)
time_offset
Apply an input time offset to this video (only valid when used as an input video in Media::Convert::Pipe). Can be used to apply A/V sync correction values.