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fre:ac


fre:ac development status update 09/2018 Drucken E-Mail
Geschrieben von: Robert   
Sonntag, den 07. Oktober 2018 um 17:47 Uhr

Hi all, this is the fre:ac development status update for September 2018.

New alpha release

I published a new alpha last month, integrating the SuperFast encoding mode and freaccmd's dynamic arguments support that I wrote about in last month's issue. With these features added, the new alpha is now almost feature complete with respect to what is planned for fre:ac 1.1 beta.

Improved tags interoperability

Several changes have been implemented to improve compatibility with tags written by other applications (most notably foobar2000). These changes enable fre:ac to extract more information from files containing such tags than previously possible. The individual improvements are:

  • Support reading and writing ID3v2 tags from/to .wav files
  • Support reading cue sheets from ID3v2 tags
  • Use album artist for artist field if only the former is set

One example where these will be useful is when ripping a CD to a single .wav file with foobar2000. Upcoming fre:ac releases will be able to list the individual tracks contained in the .wav file even if no separate .cue file is available.

Improved error handling

Despite fre:ac 1.1 alpha releases having supported parallel conversions for some time, error handling is still designed for single threaded operation. When a conversion fails, the affected thread shows an error message and the whole conversion process stops at that point.

This will be much improved in the next release. An error in one conversion will not stop the whole process any longer. Instead, error messages will be collected and displayed all in one dialog at the end of the conversion process.

In other words, when the 100th file in a 1000 files conversion job causes an error, fre:ac will continue to process the other 900 files instead of stopping the whole job. No more worrying that large unattended conversion jobs stop early without you noticing.

HiDPI improvements

Last but not least, I've also implemented some improvements for the placement of tool windows and dialogs in HiDPI mode. Dropdown lists, popup menus, tooltips and dialogs should now be displayed where you would expect them when running in scaled mode.

This concludes this month's issue. Be sure to come back in a month for the next report.

 
fre:ac development status update 08/2018 Drucken E-Mail
Geschrieben von: Robert   
Montag, den 10. September 2018 um 21:59 Uhr

So I'm really late for the monthly status update this time. Will try to post earlier next month.

There are only two things to be reported this time, but those surely are great news:

SuperFast codecs merged into mainline

The SuperFast versions of the LAME, AAC (FAAC, FDK-AAC and Core Audio), Opus and Speex codecs have finally been merged into mainline fre:ac. You still have to enable SuperFast mode manually on the Resources configuration page to make full use of them, but that option is set to become enabled by default before the fre:ac 1.1 final release.

Enabling SuperFast mode
SuperFast mode is marked experimental for now and has to be enabled manually

Read here and here for more details on fre:ac's SuperFast encoding technology.

Dynamic arguments feature merged

I wrote about the dynamic arguments feature for freaccmd in last month's issue. Now that code has been merged, making it the second big feature completed this month.

While not visible for users of the graphical UI, this will make things much easier for those who would like to script and/or automate conversions with the command line interface.

There will be a new alpha release with these changes in the next few days. Keep watching for it and stay tuned for the next update in about a month.

 
fre:ac development status update 07/2018 Drucken E-Mail
Geschrieben von: Robert   
Sonntag, den 05. August 2018 um 19:39 Uhr

Hi all, here is the July 2018 update on fre:ac development.

New alphas and SuperFast preview

There were two new alpha releases last month providing all the new features talked about in previous development status reports and fixing several issues. Unlike previous alphas, the current version is now recommended for everyone to try out. If you find any issues, please report them to support@freac.org.

There also is a new preview of the SuperFast conversion technology, this time including SuperFast LAME. If you missed the article on how SuperFast LAME is made possible, check it out here: SuperFast LAME technical details

The SuperFast technology will be included in the next regular alpha release and will then be available for everyone to use.

Dynamic encoder arguments for freaccmd

An important item on the feature list for fre:ac 1.1 beta is support for command line configuration arguments for all codecs added during fre:ac 1.1 development. Currently, freaccmd supports arguments for a very limited set of codecs only. The code to change that lives in the dynamic-arguments branches of fre:ac and BoCA and I made good progress towards merging it with the master branches in the past month.

With the new code, codecs can specify which command line arguments they support and freaccmd will make them available without the need for any codec specific code in the command line frontend itself.

Other changes

  • Improved handling of album artist in tag editor
    Handling of album artists in the tag editor has been improved to fix issues when the field is changed in album editing mode. Prior to this change this could result in the album artist information getting lost for some or all of the relevant tracks.
  • Improved adjustment of dialogs to text sizes
    Several dialogs have been reworked to adjust dynamically to the size of translated texts. The width of labels displayed in a dialog can vary greatly in different languages, so dynamic adjustment is necessary. This is not completed yet, so work on this will continue in the next few months.

That's all for this issue. Make sure to come back next month for the August status update.

 
SuperFast LAME technical details Drucken E-Mail
Geschrieben von: Robert   
Freitag, den 20. Juli 2018 um 19:27 Uhr

So I finished the SuperFast LAME multi-threaded MP3 encoder last week and it's time to write about some technical aspects of it.

tl;dr: Implementing SuperFast LAME required some additional work to handle certain features of the MP3 format. You can download a preview release of fre:ac with SuperFast LAME support from GitHub.

The challenge

SuperFast LAME is significantly more complex than the SuperFast components for AAC, Opus and Speex, mostly because of technical peculiarities of the MP3 format.

The main difficulty is that while most other formats have discrete frames of audio samples in their bitstreams, MP3 frames can overlap each other:

In this example, the average frame size is 4 blocks of data. The individual frame lengths are 4, 3, 4, 3, 1, 5, 5 and 7 blocks. In an AAC bitstream, each frame will simply have a length matching the number of data blocks required for that frame and the frames will neatly come one after another. In an MP3 bitstream, however, (at least for CBR files, VBR is more complicated) frames have a fixed size and when there is space left in a frame after all samples have been encoded, that space can be used by the following frames. This space available to following frames is called bit reservoir and allows the codec to maintain a set target quality in most cases, even when frame sizes are fixed and audio complexity changes.

Have a look at the example. The 5th frame is only one data block long and that data block fits completely into the 4th frame. It even leaves some space, so the first data block of the 6th frame starts in the 4th frame as well. Looking at only the 5th and 6th frame, their layout in the bitstream looks like this:

Here the frame headers come after the data and in case of frame #5, there even is data of another frame (#6) between its data and its header. In real world MP3 streams, the situation can be even more intricate.

Basic SuperFast operation

So this is a problem when implementing the SuperFast technology for MP3. SuperFast works by passing chunks of audio data to separate encoder instances and later joining the encoded data blocks back together in the right order. This requires the frames to be available in discrete form in order to deal with overlap and joining the frames correctly. The SuperFast encoding loop usually looks like this (click to jump to example source code):

  1. Find next worker thread and wait until it is ready
  2. Check if worker thread has encoded frames
    a. Skip overlap frames
    b. Write other frames to output stream
  3. Pass next chunk of audio to worker thread

MP3 difficulties

When dealing with MP3, multiple issues arise from the peculiarities around the bit reservoir:

  • The encoder might not return all encoded frames after processing a chunk of data as some frames might still be waiting for additional data to put in the bit reservoir.
  • Frames are not available in discrete form, but may be overlapping each other.
  • After dealing with the above, frames need to be put back into an MP3 compatible bitstream after joining.
  • Frames might require more reservoir than is available after joining with frames coming from other codec instances.

Previous attempts to create multi-threaded MP3 encoders dealt with these issues in a very simple way: They completely disabled the bit reservoir to get nicely laid out frames with no overlapping data. This solution cuts into the resulting MP3's quality, though, which is why such encoders never really gained traction.

So let's see how we can handle these issues more adequately.

Unraveling it

The first one is relatively simple. After encoding a chunk of data, we call lame_encode_flush_no_gap to force the encoder to return all encoded frames even if they are not completely filled yet. This makes sure we can operate with all the relevant frames in the next steps.

The second issue is handled by a bitstream unpacker that parses the data returned by the encoder and extracts discrete frames from the bitstream. After this step all frames will be laid out as a frame header followed by the complete data belonging to that frame. No more intermixing with other frames' headers or data.

After unpacking, we are ready to perform overlap skipping and ordering of data chunks from different encoder instances.

When writing the ordered frames to the output stream, we now need to make sure to repack them back into an MP3 compatible bitstream. The repacker deals with frame sizes and the bit reservoir and tries to pack frames in the most compact way.

Sometimes, though, a frame requires more reservoir than is currently available and the repacker needs to find a way to fit it in. It basically has two options to accomplish this: If only a few extra bits are needed, the repacker can add padding to a frame. This will add an additional byte and sometimes this is enough to provide the required reservoir. In cases where it is not sufficient, the repacker can enlarge one or more previous frames to a bigger frame size. This usually allows to provide enough reservoir, but requires all affected frames to be repacked again.

However, even this might not be enough when issue number 4 comes into play. In some rare cases, a frame requires so much reservoir that it is simply not possible to fit it into the bitstream. This can happen because one encoder instance cannot know how much reservoir will be left over by the instance encoding the preceding chunk. In cases where the preceding instance has to deal with a difficult to encode signal, it might leave next to no reservoir available to the next encoder.

Dealing with this was difficult. While there are some simple options like forcing the encoder to use a lower bitrate, these might potentially result in audible quality drops. So I tried to find another way to handle this.

Basically, the SuperFast algorithm will try to re-encode the audio part starting with the non-fitting frame and repeat this until it fits. To work around situations where it might never fit using this strategy, each time it fails, we try to put some more pressure on the bit reservoir by prepending a few frames of difficult to encode dummy data. These dummy frames force the encoder to spend some reservoir on them and lead to using less reservoir for our previously non-fitting frame, eventually allowing us to fit the frame into the bitstream.

The result

With all these additional steps, the process for SuperFast LAME now looks like this (click to jump to source code):

  1. Get next worker thread and wait until it is ready
  2. Check if worker thread has encoded frames
    a. Unpack frames
    b. Skip overlap frames
    c. Repack other frames
    i. If successful, continue with 2d
    ii. Write completed frames to output stream
    iii. Put increasing pressure on the reservoir
    iv. Re-encode starting from failed frame
    v. Continue with 2a
    d. Write repacked frames to output stream
  3. Pass next chunk of audio to worker thread

Arriving at this point took several months of work, but was absolutely worth it. The SuperFast LAME encoder scales well with the number of CPU cores and can provide a 3.5x speedup on a quad-core processor. On my 8 core, 16 thread CPU, I was able to achieve up to 12x speed increase with it.

Unlike previous attempts to speed up MP3 encoding, SuperFast LAME does this while still using the MP3 format's bit reservoir feature and uses an unmodified encoder library - the necessary changes are all implemented in the frontend application and could be used with alternative MP3 encoders as well.

I plan to implement this technology on top of the command line LAME frontend in the future. For now, my priority is on releasing fre:ac 1.1 beta and final versions, though. But keep watching this blog for future annoucements about a SuperFast enabled stand-alone LAME version.

Downloads

SuperFast LAME is now in testing and included in the SuperFast Preview Release 3 available at GitHub.

Source code

Check out the SuperFast repository on GitHub if you would like to learn more or build the code yourself. The SuperFast LAME implementation can be found in the components/lame folder.

 
fre:ac development status update 06/2018 Drucken E-Mail
Geschrieben von: Robert   
Mittwoch, den 04. Juli 2018 um 23:39 Uhr

The June development update is overdue, but better late than never, here it is. It was a very productive month, so let's get right to the good stuff.

Parallel conversion jobs

The current alpha release supports only one conversion job at a time. Multiple tracks in a conversion can be processed in parallel, but when you try to start a new job while a conversion is still running, you just get a message asking if you would like to schedule the new job for after the current one is finished.

The next release will enable parallel conversion jobs. As long as there are CPU threads left, multiple conversions, possibly using different settings, can run at the same time. This helps when converting multiple albums to a single file per album or when ripping CDs using multiple drives.

Improved handling of automatic ripping

This brings us to the next item. There are some issues with the current alpha when using the automatic ripping option with multiple drives. When inserting a disc while other tracks are still in the joblist, the new ripping job will try to process those other tracks again, leading to some tracks being ripped more than once. Also, the new job will not start before any currently running rip is finished. Both issues will be fixed in the next alpha which makes ripping with multiple drives much more usable.

Fixed metadata bug with Core Audio on Windows

In May, a user opened an issue on GitHub reporting that when converting ALAC files to AAC using the Core Audio encoder on Windows, tags were missing on some files. I could easily reproduce the issue, but it seemed really strange. It occurred only when converting files decoded with an external decoder (i.e. a separate .exe called by fre:ac) and the selected encoder was Core Audio. That didn't seem to make any sense at first.

It turned out to actually be a bug in Apple's Core Audio implementation on Windows. It would make file handles created by its API calls inheritable by sub-processes. The sub-processes (in this case the external decoders) would then inherit any open handles and lock the respective files, making them unwritable by the tagger component.

Making handles inheritable is something that an API never should do as it can lead to unforeseeable behavior and very difficult to analyze bugs.

Fortunately there is a work-around by avoiding the problematic APIs. The next alpha release will include this fix.

Automatic codec builds

Till now, all the codecs included with fre:ac are built manually: Set the correct compiler flags for each codec on each supported OS, apply necessary patches, configure the codecs with the right flags and run make to build them. This costs a lot of time whenever a new codec version is relased and also is a bit error-prone, so it was necessary to change it.

I built a script to automate all the steps listed above for most of the necessary codecs and some other libraries. The script can compile FAAC, FAAD2, FDK-AAC, FLAC, LAME, libav, libogg, libsamplerate, libsndfile, Monkey's Audio, mpg123, Opus, RubberBand, Speex, Vorbis and WavPack on Windows, macOS, Linux and FreeBSD. Whenever a new version of one of these libraries is released in the future, I can simply update the package download URL and run the script to build a new release.

The script can be found in the source repository on GitHub.

Reworked donation dialog

The donation dialog has been reworked to support more payment types. Previously supporting only PayPal, the new dialog adds support for Donorbox, SEPA transfers and the Bitcoin and Ethereum crypto currencies.

Other items

A number of other changes have been implemented in the past month, the most notable of which are:

  • HiDPI icons
    Preparing for the upcoming beta release, I added higher quality versions of the toolbar icons that now look crisp on HiDPI displays like Apple's Retina screens.
  • Completely translatable
    In the current alpha release, not all strings are translatable. This applies to configuration dialogs for external codecs especially. The next alpha will fix this and enable translations for WavPack, Musepack, OptimFROG and TAK configuration dialogs along with some other previously untranslatable strings.
  • Fixed MP4 metadata bug
    When converting multiple files in parallel to AAC or ALAC output, it can happen that some files end up being unoptimized due to a bug in the MP4v2 library used by fre:ac. Optimization of MP4 files means that tags and the seektable are moved to the beginning of the file for more efficient processing. The next alpha release will include a work-around for the MP4v2 bug fixing the issue of MP4 files not being optimized.
  • Downloads now hosted on GitHub
    The links on the downloads page now point to GitHub instead of SourceForge. This enables direct downloads without an intermediate page to choose a mirror and allows downloading using right-click + save as.

SuperFast LAME status

There were some open issues with the SuperFast LAME implementation when I last wrote about it in the April status update. These have been fixed now and there will be another SuperFast preview release including LAME support very soon after the next alpha. I'm also preparing a technical article about how the MP3 bit reserviour is handled in SuperFast LAME. This should be out within one week from now.

That's it for this month. Be sure to come back in about one month for the next update.

 
fre:ac development status update 05/2018 Drucken E-Mail
Geschrieben von: Robert   
Donnerstag, den 31. Mai 2018 um 22:35 Uhr

Hi all, it's time for an update on fre:ac development again. The past month was quite productive and so I have lots of things to talk about.

Integration with Travis CI

The GitHub projects for the smooth Class Library, BoCA and fre:ac are now integrated with the Travis CI platform for automated build tests. Every commit to one of these repositories now starts automatic build processes on Linux and macOS to check if anything got broken. This improves the development process by ensuring that build-breaking issues will be noticed quickly.

The build processes are also started for pull requests, so anyone who submits a patch can immediately see if it breaks anything.

Fast CRC patches accepted into FLAC and Ogg

The patches for faster CRC calculations I wrote about last month have been accepted by the upstream FLAC and Ogg projects. So with the next FLAC and Ogg releases, any software using them will benefit from faster encoding and decoding.

Allowing playback during conversions

Until now, it's not possible to play a track in fre:ac while a conversion is running. This limitation will be lifted with the next alpha release. You will be able to play tracks during conversions as long as they are not on a CD that is currently being ripped from.

Faster AAC, APE and WMA encoding

fre:ac's AAC, Monkey's Audio (APE) and WMA encoder components use temporary files for writing output data. The content of these files is transferred to the actual output file after the encoding process is finished which causes a small delay at the end of each conversion. The next alpha release will fix this by writing directly to the actual output file from the start.

Making this possible required an addition to the internal IO filter interface and extensive testing. This is why it was not done like this earlier.

Improved handling of album artists

Starting with the next alpha release, fre:ac will make use of the <albumartist> placeholder in the default output filename pattern. This prevents the creation of separate folders for each track when dealing with sampler CDs. On samplers, the previously used <artist> placeholder would resolve to a different artist for each track, while <albumartist> will usually be something like Various artists and be the same for every track.

SourceForge Project of the Month

fre:ac has been chosen as the SourceForge Project of the Month of May 2018. This is the second time fre:ac won this award after October 2015. You can read a short interview with me in the SourceForge blog.

This closes this month's issue. Be sure to come back in June for another update.

 
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