International organisation for standardisation

Creation of Task Groups

Task groups were convened for the duration of the MPEG meeting, as shown in 3. Results of task group activities are reported below.

Approval of previous meeting report

The Chair asked for approval of the 95^th Audio Subgroup meeting report, which was registered as a contribution. The report was approved.

Review of AHG reports

There were no requests to review any of the AHG reports.

Joint meetings

Groups	What	Where	Day	Time
S, A	USAC Audio/Systems Interaction	Systems	Tue	1400-1500
All	MMT	Rm 18	Wed	1600-1730
R, A	Audio for HEVC	Audio	Thu	1000-1100

Received National Body Comments and Liaison matters

No.	Title	Source	Responding
m19533	IEC NP: Audio Archive System -- Part 1: Physical format -- Part 2: Audio archive system	IEC TC 100 via SC 29 Secretariat	S.R. Quackenbush
m19534	IEC NP: Text-to-Speech Functionality for Television - General requirements	IEC TC 100 via SC 29 Secretariat	S.R. Quackenbush
m19538	IEC CDV 61937-2/Amd.1	IEC TC 100 via SC 29 Secretariat	S.R. Quackenbush

Plenary Discussion

There were none.

3Record of AhG meetings

There were no AhG meetings.

4Task group activities

Joint Meeting

With Systems on USAC Audio/Systems Interactions (Tue 1400-1500)

Schuyler Quackenbush, Audio Research Labs, presented

m19972

Thoughts on USAC /systems interaction

S. R. Quackenbush

This contribution proposes means to achieve the following functionality:

• 
  Exact Round-Trip Coding. Given an arbitrary input signal, e.g. as a *.wav file, any compliant USAC encoder can encode to an MPEG-4 File and a USAC decoder, with the help of some “out of scope” but simple Systems level functionality, can decode the file such that the exact same signal is obtained.
  
• 
  File Random Access and Signal Excerpt. Building upon the Exact Round-Trip Coding functionality, a USAC decoder, with the help of some “out of scope” but simple Systems level functionality, can efficiently reconstruct an arbitrary, sample-exact excerpt of the compressed waveform.
  

There was very good discussion between Audio and Systems experts about the objectives (e.g. to understand the definition of round-trip-coding), the mechanism (e.g. what boxes in the MPEG-4 File Format are needed to support the functionality) and, most importantly, the need for the functionality.

The following is a summary of the widely-expressed views in the joint meeting:

Since round-trip coding is well defined and has a very apparent value in the context of file-based processing of time-domain and compressed waveforms, there was considerable support for an EditListBox in all MPEG-4 Files containing a USAC bitstream.

There was less support for an EditListBox, SyncSampleBox, SampleToGroup box and the SampleGroupDescription box (where the last contains an AudioSampleGroupEntry which contains a AudioRollRecoveryEntry which contains the roll_distance value) in MPEG-4 Files containing a USAC bitstream.

It was remarked that if the desired access unit is chosen exactly on a random access point, (or even the access unit immediately after the random access point), then the sound signal must be decoded from the PRECEDING random access point, because of the pre-roll due to the MDCT transform.

Finally, there was wide agreement that the concepts of round-trip and random excerpt did not have much utility in a streaming environment (i.e. with no MPEG-4 file).

Further Discussion in Audio Subgroup

Based on the information gathered in the joint meeting, it was decided that Audio experts should study the proposal of mandating EditListBox in MP4F, with the intention of a decision at the next MPEG meeting. There are two specific issues to study: 1) how to mandate that USAC bitstreams in an MPEG-4 File shall have an EditListBox with appropriate information to support round-trip coding and 2) how the USAC standard should indicate proper use of the EditListBox. To address the second issue, the presenter expressed the intention of bring a contribution to the next meeting containing text appropriate for inclusion in the informative part of the USAC specification.