This page tests seamlessly looping playback of a good quality 44.1kHz music clip with an intro and custom loop points. Files:

biomechanics_44100hz_256kbs_stereo.mp3: Downloaded from https://www.dl-sounds.com/royalty-free/, license: https://www.dl-sounds.com/license/. The original file without looping.

In the following files, the loop should start at sample 1 499 996 (inclusively), and end at sample 3 970 030 (exclusively). That is, after sample 3 970 029, the next played sample should be sample 1 499 996.
biomechanics_intro_looping_44100hz_197kbs_stereo_lame3.99.mp3: Adapted from biomechanics_44100hz_256kbs_stereo.mp3 by adding a custom loop point. Encoded with Audacity 2.1.3 Win64 + Lame MP3 encoder 3.99.3, with options Bit Rate Mode: Preset, Quality: Standard 170-210 kbps, Variable Speed: Fast, Channel Mode: Joint Stereo
biomechanics_intro_looping_44100hz_320kbs_stereo.ogg: Converted from biomechanics_intro_looping_44100hz_197kbs_stereo_lame3.99.mp3 with Audacity 2.1.3 Win64, with option Quality: 9
biomechanics_intro_looping_44100hz_196kbs_stereo_ffmpeg2.2.2_aac.m4a: Converted from biomechanics_intro_looping_44100hz_197kbs_stereo_lame3.99.mp3 with Audacity 2.1.3 Win64 + FFmpeg 2.2.2, with option Quality: 300

Play uncompressed (Web Audio + AudioBufferSourceNode + decodeAudioData() to AudioBuffer):

Play compressed (<audio> element playing a Blob embedded as MediaElementAudioSource to Web Audio graph):

Current memory usage: 0 bytes.