What do you mean by step 1 "alter the behavior ... as chrome"?

I can't play this file in Chrome 49.0.2623.112 (Official Build) (64-bit) on my Linux machine while local media player application handles it fine.

chrome://media-internals reports the following:

render_id: 464
player_id: 0
pipeline_state: kPlaying
event: PAUSE
url: file:///usr/local/.../test.mp4
total_bytes: 4206633
streaming: false
single_origin: true
passed_cors_access_check: false
range_header_supported: false
error: FFmpegDemuxer: failed creating video stream
info: FFmpegDemuxer: created audio stream, config codec: aac bytes_per_channel: 4 channel_layout: 3 samples_per_second: 44100 sample_format: 6 bytes_per_frame: 8 seek_preroll: 0ms codec_delay: 0 has extra data? true encrypted? false
duration: 5.852
found_audio_stream: true
audio_sample_format: Float 32-bit planar
audio_codec_name: aac
audio_channels_count: 2
audio_samples_per_second: 44100
found_video_stream: false
max_duration: 5.852
start_time: 0
bitrate: 5750694
audio_dds: false
audio_decoder: FFmpegAudioDecoder

I set a few GYP flags(ppmpeg_branding='chrome')which can alter the behaviour of Chromium's HTML5 audio/video implemention. So Chromium can support some mp4 file.

You need ffmpeg_branding="Chrome" and proprietary_codecs=true

Dale, the file attached in the OP doesn't play in the official Chrome builds I tried (like Chrome 52 on Mac or 49 on Linux). I don't think it's the build flags issue, rather an mp4 that can't be played.

Ah yeah that won't help either :) The file is mpeg4 and not h264, so in order to play that in desktop Chrome you'll need to set ffmpeg_branding="ChromeOS"

(That will only work on Linux though)