slow, scratchy video previews on CRT but not HDMI

ohmycommodore

Hi folks,

Heads up that this applies to a pre-built image I'm fiddling with in order to learn some new things I haven't encountered before, in case they are useful for my main setup.

All systems and games are working fine on CRT via composite cable, and as well on our modern LCD via HDMI. One big difference though, is that on CRT the video previews play slow and sound scratchy. It looks and feels very similar to an N64 rom struggling.

Any thoughts on why this happens or if there's a remedy? Am I ignoring something simple here?

If it matters, there are lots of roms and thus lots of preview videos on this image, though the card has plenty of room to spare.

This setup includes Pi 3B+ / RetroPie 4.4.4 / USB controllers / 2.5 amp power supply / Kano bluetooth keyboard with USB dongle.

I'll try to paste my config.txt below. If it's not part of the issue, I'm still happy to have someone give it a look. The goal is to have a system that will stay on the CRT, but can move without any fuss to an LCD on occasion – either at home, on the road in a hotel, etc.

Since this was from a pre-built image, there may in fact be a couple of lines that I do or don't need included. Again, just learning along the way here :)

ohmycommodore

For more options and information see http://rpf.io/configtxtreadme.

Some settings may impact device functionality. See link above for details.

disable_splash=1

Uncomment if you get no picture on HDMI, for a default "safe" mode.

#hdmi_safe=1

Uncomment if your display has a black border of unused pixels visible and your display can output without overscan.

disable_overscan=0

Uncomment to adjust overscan. Use positive numbers if console goes off screen, and negative if there is too much border.

overscan_left=10
overscan_right=10
overscan_top=4
overscan_bottom=4

Uncomment to force a console size. By default it will be display's size minus overscan.

#framebuffer_width=1280
#framebuffer_height=720

Uncomment if hdmi display is not detected and composite is being output.

#hdmi_force_hotplug=1

Uncomment to force a specific HDMI mode (this will force VGA).

#hdmi_group=2
#hdmi_mode=9

Uncomment to force a HDMI mode rather than DVI. This can make audio work in DMT (computer monitor) modes.

#hdmi_drive=2

Uncomment to increase signal to HDMI, if you have interference, blanking, or no display.

#config_hdmi_boost=4

Uncomment for composite PAL.

#sdtv_mode=2

Uncomment to overclock the arm. 700 MHz is the default.

#arm_freq=800

Uncomment some or all of these to enable the optional hardware interfaces.

#dtparam=i2c_arm=on
#dtparam=i2s=on
#dtparam=spi=on

Uncomment this to enable the lirc-rpi module.

#dtoverlay=lirc-rpi

Additional overlays and parameters are documented /boot/overlays/README.

Enable audio (loads snd_bcm2835).

dtparam=audio=on
#gpu_mem_256=128
#gpu_mem_512=256
#gpu_mem_1024=256
gpu_mem=512

Uncomment for analog audio hiss fix.

audio_pwm_mode=2

Uncomment to force emulationstation to obey the same overscan settings as the console.

overscan_scale=1

A Former User

You can't get help here for pre-made images, you will need to go back to the person who made it. Nobody here knows how it was built, what tweaks have been done, or if any custom settings have been applied. Only the person who made the image will know this.
Saying that, try adding these to the config.txt.

audio_pwm_mode=0
disable_audio_dither=1

ohmycommodore

Some further searching with different terms gives me these links from earlier this year, regarding what appears to be the same problem:

https://retropie.org.uk/forum/topic/17107/bug-solved-omxplayer-on-stretch-based-builds-stutters-on-composite
https://sudomod.com/forum/viewtopic.php?f=44&t=5953&sid=a445fc61f5d69f18b005c1318d303f41&start=10
https://github.com/popcornmix/omxplayer/issues/625

A quick scan of them shows a bug in OMX player that affects composite only... and yes, OMX is turned on in this image I'm playing with.

I'll have a full read and a tinker later.

ohmycommodore

@John_RM_70 said in slow, scratchy video previews on CRT but not HDMI:

audio_pwm_mode=0
disable_audio_dither=1

Yes that appears to fix things, addressing the root cause, which is the bug I linked to above. Thanks.