UserAgent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/70.0.3538.102 Safari/537.36

Example URL:
Any that I've come across; mostly YouTube

Steps to reproduce the problem:
1. Try to play video
2. Chrome makes up its own mind whether to play or stop the video when I'm doing UNRELATED things
3. Frustration!

What is the expected behavior?
It's really very simple.
PLAY MEANS PLAY.
STOP MEANS STOP.
NOTHING BUT PLAY MEANS PLAY.
NOTHING BUT STOP MEANS STOP.
***ONE*** exception: you can stop at the end of the video.
END OF VIDEO DOES NOT MEAN PICK SOME RANDOM OTHER VIDEO AND START PLAYING IT.
OPENING A TAB WITH A VIDEO IN IT DOES NOT MEAN 'PLAY VIDEO' because I might have some other music going on, eg in VLC.

I realise different people want different things so most of this will need to go into various settings.

What went wrong?
(1) Video playing in Tab A.  I'm in Tab B which is not video related.  I switch to tab C which is not video related.  Tab A stops playing.
(2) Fucking Autoplay keeps switching itself back on!!!! I have to install an extension to stop this confounded behaviour.  NO AUTOPLAY!!!!!!!!!
(3) Video is playing in Tab A.  I'm in Tab B.  I open new Tab C to Google something.  Video stops playing.
(4) Open some news source with some shitty advert or article video.  Video starts playing.  I DID NOT PRESS PLAY - DO NOT START PLAYING!  DO NOT EVEN START DOWNLOADING IT! Because I'm sometimes mobile and this stupid advert that I'm not going to buy anyway or news (w)anchor blathering on about bollocks takes up some of my LIMITED data, meaning I have to pay extra to watch something I could have watched as part of my included data before.

Did this work before? N/A 

Is it a problem with Flash or HTML5? N/A

Does this work in other browsers? Yes

Chrome version: 70.0.3538.102  Channel: n/a
OS Version: 10.0
Flash Version: 

Contents of chrome://gpu: 

Graphics Feature Status
Canvas: Hardware accelerated
Flash: Hardware accelerated
Flash Stage3D: Hardware accelerated
Flash Stage3D Baseline profile: Hardware accelerated
Compositing: Hardware accelerated
Multiple Raster Threads: Enabled
Native GpuMemoryBuffers: Software only. Hardware acceleration disabled
Out-of-process Rasterization: Disabled
Hardware Protected Video Decode: Hardware accelerated
Rasterization: Hardware accelerated
Skia Deferred Display List: Disabled
Skia Renderer: Disabled
Surface Synchronization: Enabled
Video Decode: Hardware accelerated
Viz Service Display Compositor: Disabled
WebGL: Hardware accelerated
WebGL2: Hardware accelerated
Driver Bug Workarounds
clear_uniforms_before_first_program_use
decode_encode_srgb_for_generatemipmap
disable_discard_framebuffer
disable_framebuffer_cmaa
exit_on_context_lost
force_cube_complete
msaa_is_slow
scalarize_vec_and_mat_constructor_args
disabled_extension_GL_KHR_blend_equation_advanced
disabled_extension_GL_KHR_blend_equation_advanced_coherent
Problems Detected
Some drivers are unable to reset the D3D device in the GPU process sandbox
Applied Workarounds: exit_on_context_lost
Clear uniforms before first program use on all platforms: 124764, 349137
Applied Workarounds: clear_uniforms_before_first_program_use
Always rewrite vec/mat constructors to be consistent: 398694
Applied Workarounds: scalarize_vec_and_mat_constructor_args
ANGLE crash on glReadPixels from incomplete cube map texture: 518889
Applied Workarounds: force_cube_complete
On Intel GPUs MSAA performance is not acceptable for GPU rasterization: 527565
Applied Workarounds: msaa_is_slow
Framebuffer discarding can hurt performance on non-tilers: 570897
Applied Workarounds: disable_discard_framebuffer
Use GL_INTEL_framebuffer_CMAA on ChromeOS: 535198
Applied Workarounds: disable_framebuffer_cmaa
Disable KHR_blend_equation_advanced until cc shaders are updated: 661715
Applied Workarounds: disable(GL_KHR_blend_equation_advanced), disable(GL_KHR_blend_equation_advanced_coherent)
Decode and Encode before generateMipmap for srgb format textures on Windows: 634519
Applied Workarounds: decode_encode_srgb_for_generatemipmap
Native GpuMemoryBuffers have been disabled, either via about:flags or command line.
Disabled Features: native_gpu_memory_buffers
Viz service display compositor is not enabled by default.
Disabled Features: viz_display_compositor
Skia renderer is not used by default.
Disabled Features: skia_renderer
Skia deferred display list is not used by default.
Disabled Features: skia_deferred_display_list
Version Information
Data exported	2018-11-22T11:17:43.970Z
Chrome version	Chrome/70.0.3538.102
Operating system	Windows NT 10.0.17134
Software rendering list URL	https://chromium.googlesource.com/chromium/src/+/4bbeebac88fdc09c97265e47c205868bbd190497/gpu/config/software_rendering_list.json
Driver bug list URL	https://chromium.googlesource.com/chromium/src/+/4bbeebac88fdc09c97265e47c205868bbd190497/gpu/config/gpu_driver_bug_list.json
ANGLE commit id	05c729f336ef
2D graphics backend	Skia/70 8adc53ec0ee4bbafbd9925024df38437c0fcf88a-
Command Line	"C:\Program Files (x86)\Google\Chrome\Application\chrome.exe" --flag-switches-begin --autoplay-policy=document-user-activation-required --flag-switches-end
Driver Information
Initialization time	349
In-process GPU	false
Passthrough Command Decoder	false
Sandboxed	true
GPU0	VENDOR = 0x8086 [Google Inc.], DEVICE= 0x5912 [ANGLE (Intel(R) HD Graphics 630 Direct3D11 vs_5_0 ps_5_0)] *ACTIVE*
Optimus	false
AMD switchable	false
Desktop compositing	Aero Glass
Direct Composition	true
Supports overlays	true
Overlay capabilities
NV12	SCALING
YUY2	SCALING
Diagonal Monitor Size of \\.\DISPLAY2	27.0"
Diagonal Monitor Size of \\.\DISPLAY1	23.5"
Driver D3D12 feature level	D3D 12.1
Driver Vulkan API version	Vulkan API 1.1.0
Driver vendor	Intel Corporation
Driver version	24.20.100.6286
Driver date	8-15-2018
GPU CUDA compute capability major version	0
Pixel shader version	5.0
Vertex shader version	5.0
Max. MSAA samples	16
Machine model name	
Machine model version	
GL_VENDOR	Google Inc.
GL_RENDERER	ANGLE (Intel(R) HD Graphics 630 Direct3D11 vs_5_0 ps_5_0)
GL_VERSION	OpenGL ES 2.0 (ANGLE 2.1.0.05c729f336ef)
GL_EXTENSIONS	GL_ANGLE_client_arrays GL_ANGLE_depth_texture GL_ANGLE_explicit_context GL_ANGLE_explicit_context_gles1 GL_ANGLE_framebuffer_blit GL_ANGLE_framebuffer_multisample GL_ANGLE_instanced_arrays GL_ANGLE_lossy_etc_decode GL_ANGLE_pack_reverse_row_order GL_ANGLE_program_cache_control GL_ANGLE_request_extension GL_ANGLE_robust_client_memory GL_ANGLE_texture_compression_dxt3 GL_ANGLE_texture_compression_dxt5 GL_ANGLE_texture_usage GL_ANGLE_translated_shader_source GL_CHROMIUM_bind_generates_resource GL_CHROMIUM_bind_uniform_location GL_CHROMIUM_color_buffer_float_rgb GL_CHROMIUM_color_buffer_float_rgba GL_CHROMIUM_copy_compressed_texture GL_CHROMIUM_copy_texture GL_CHROMIUM_sync_query GL_EXT_blend_minmax GL_EXT_color_buffer_half_float GL_EXT_debug_marker GL_EXT_discard_framebuffer GL_EXT_disjoint_timer_query GL_EXT_draw_buffers GL_EXT_frag_depth GL_EXT_map_buffer_range GL_EXT_occlusion_query_boolean GL_EXT_read_format_bgra GL_EXT_robustness GL_EXT_sRGB GL_EXT_shader_texture_lod GL_EXT_texture_compression_dxt1 GL_EXT_texture_compression_s3tc_srgb GL_EXT_texture_filter_anisotropic GL_EXT_texture_format_BGRA8888 GL_EXT_texture_rg GL_EXT_texture_storage GL_EXT_unpack_subimage GL_KHR_debug GL_KHR_parallel_shader_compile GL_NV_EGL_stream_consumer_external GL_NV_fence GL_NV_pack_subimage GL_NV_pixel_buffer_object GL_OES_EGL_image GL_OES_EGL_image_external GL_OES_compressed_ETC1_RGB8_texture GL_OES_depth32 GL_OES_element_index_uint GL_OES_get_program_binary GL_OES_mapbuffer GL_OES_packed_depth_stencil GL_OES_rgb8_rgba8 GL_OES_standard_derivatives GL_OES_surfaceless_context GL_OES_texture_float GL_OES_texture_float_linear GL_OES_texture_half_float GL_OES_texture_half_float_linear GL_OES_texture_npot GL_OES_vertex_array_object OES_compressed_EAC_R11_signed_texture OES_compressed_EAC_R11_unsigned_texture OES_compressed_EAC_RG11_signed_texture OES_compressed_EAC_RG11_unsigned_texture OES_compressed_ETC2_RGB8_texture OES_compressed_ETC2_RGBA8_texture OES_compressed_ETC2_punchthroughA_RGBA8_texture OES_compressed_ETC2_punchthroughA_sRGB8_alpha_texture OES_compressed_ETC2_sRGB8_alpha8_texture OES_compressed_ETC2_sRGB8_texture
Disabled Extensions	GL_KHR_blend_equation_advanced GL_KHR_blend_equation_advanced_coherent
Disabled WebGL Extensions	
Window system binding vendor	Google Inc. (adapter LUID: 000000000000a7e6)
Window system binding version	1.4 (ANGLE 2.1.0.05c729f336ef)
Window system binding extensions	EGL_EXT_create_context_robustness EGL_ANGLE_d3d_share_handle_client_buffer EGL_ANGLE_d3d_texture_client_buffer EGL_ANGLE_surface_d3d_texture_2d_share_handle EGL_ANGLE_query_surface_pointer EGL_ANGLE_window_fixed_size EGL_ANGLE_keyed_mutex EGL_ANGLE_surface_orientation EGL_ANGLE_direct_composition EGL_NV_post_sub_buffer EGL_KHR_create_context EGL_EXT_device_query EGL_KHR_image EGL_KHR_image_base EGL_KHR_gl_texture_2D_image EGL_KHR_gl_texture_cubemap_image EGL_KHR_gl_renderbuffer_image EGL_KHR_get_all_proc_addresses EGL_KHR_stream EGL_KHR_stream_consumer_gltexture EGL_NV_stream_consumer_gltexture_yuv EGL_ANGLE_flexible_surface_compatibility EGL_ANGLE_stream_producer_d3d_texture EGL_ANGLE_create_context_webgl_compatibility EGL_CHROMIUM_create_context_bind_generates_resource EGL_CHROMIUM_sync_control EGL_EXT_pixel_format_float EGL_KHR_surfaceless_context EGL_ANGLE_display_texture_share_group EGL_ANGLE_create_context_client_arrays EGL_ANGLE_program_cache_control EGL_ANGLE_robust_resource_initialization EGL_ANGLE_create_context_extensions_enabled
Direct rendering	Yes
Reset notification strategy	0x8252
GPU process crash count	0
Compositor Information
Tile Update Mode	One-copy
Partial Raster	Enabled
GpuMemoryBuffers Status
ATC	Software only
ATCIA	Software only
DXT1	Software only
DXT5	Software only
ETC1	Software only
R_8	Software only
R_16	Software only
RG_88	Software only
BGR_565	Software only
RGBA_4444	Software only
RGBX_8888	GPU_READ, SCANOUT
RGBA_8888	GPU_READ, SCANOUT
BGRX_8888	Software only
BGRX_1010102	Software only
RGBX_1010102	Software only
BGRA_8888	Software only
RGBA_F16	Software only
YVU_420	Software only
YUV_420_BIPLANAR	Software only
UYVY_422	Software only
Display(s) Information
Info	Display[2528732444] bounds=[-1920,0 1920x1080], workarea=[-1920,0 1920x1040], scale=1, external.
Color space information	{primaries_d50_referred: [[0.6524, 0.3321], [0.3438, 0.6147], [0.1599, 0.0757]], transfer:0.0000*x + 0.0000 if x < 0.0000 else (1.0000*x + 0.0000)**2.1992 + 0.0000, matrix:RGB, range:FULL}
Bits per color component	8
Bits per pixel	24
Info	Display[2779098405] bounds=[0,0 1920x1080], workarea=[0,0 1920x1040], scale=1, external.
Color space information	{primaries:BT709, transfer:IEC61966_2_1, matrix:RGB, range:FULL}
Bits per color component	8
Bits per pixel	24
Video Acceleration Information
Decode h264 baseline	up to 4096x2304 pixels
Decode h264 baseline	up to 2304x4096 pixels
Decode h264 main	up to 4096x2304 pixels
Decode h264 main	up to 2304x4096 pixels
Decode h264 high	up to 4096x2304 pixels
Decode h264 high	up to 2304x4096 pixels
Decode vp8	up to 7680x4320 pixels
Decode vp8	up to 4320x7680 pixels
Decode vp9 profile0	up to 7680x4320 pixels
Decode vp9 profile0	up to 4320x7680 pixels
Decode vp9 profile1	up to 7680x4320 pixels
Decode vp9 profile1	up to 4320x7680 pixels
Decode vp9 profile2	up to 7680x4320 pixels
Decode vp9 profile2	up to 4320x7680 pixels
Decode vp9 profile3	up to 7680x4320 pixels
Decode vp9 profile3	up to 4320x7680 pixels
Encode h264 baseline	up to 3840x2176 pixels and/or 30.000 fps
Encode h264 main	up to 3840x2176 pixels and/or 30.000 fps
Encode h264 high	up to 3840x2176 pixels and/or 30.000 fps
Diagnostics
... loading ...
Log Messages
GpuProcessHostUIShim:
[90744:84832:1122/090944.219:WARNING:angle_platform_impl.cc(59)] : compileToBinary(235): C:\fakepath(67,9-52): warning X3571: pow(f, e) will not work for negative f, use abs(f) or conditionally handle negative values if you expect them
[90744:23740:1122/090944.231:WARNING:angle_platform_impl.cc(59)] : compileToBinary(235): C:\fakepath(65,23-43): warning X3571: pow(f, e) will not work for negative f, use abs(f) or conditionally handle negative values if you expect them

You need to understand something about an audiophile listening to music: the music must continue uninterrupted.  That means Chrome has to behave predictably and not try to guess what I want.  Which means playing only on play request, and stopping only on stop request.  Your current algorithm, extremely clever I'm sure, consistently guesses wrongly.  Consequently I'm giving up on Chrome for YouTube.  Firefox seems to work as I want.