OutOfMemory while recording 4K video to low class SD card

[Eugene B]

When recording 4K video to a low-class (e.g., Class 4) SD card, the video stream continuously fills the internal buffer faster than the data can be written to the slow storage medium. This quickly leads to a system-level low memory condition. To maintain overall OS functionality, Android's process management then terminates all background and, eventually, foreground processes, including the camera app.

The SD card specification does not provide a standardized way to query the card's speed class directly. Therefore, the application cannot retrieve this information reliably. While we could theoretically perform a write speed test ourselves, implementing such a feature seems out of scope for a core Camera application.

I have reviewed the CameraX API but could not find a method to obtain the size of the VideoRecorder's internal buffer. The VideoRecordEvent.RecordingStats only provides information about the number of bytes written.

Question: Is there any way to access or determine the size of the VideoRecorder buffer in CameraX?

13:21:54.723   300   300 I lowmemorykiller: Kill 'com.some.store:AppMetrica' (19951), uid 10029, oom_score_adj 945 to free 31888kB rss, 55172kB swap; reason: min watermark is breached and thrashing (109%)
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13:21:55.445   300   300 W lowmemorykiller: Failed to open /proc/20255/oom_score_adj; errno=2: process 20255 might have been killed
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13:21:56.669   630 21208 I DropBoxManagerService: add tag=system_server_lowmem isTagEnabled=true flags=0x6
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[Scott Nien]

Hi there, 

This seems something we can improve. 

Can you share more information to us? 

1) What devices are you using 
2) What is the purpose of recording 4K videos on a sd card? Is this a key user journey in your app or is it reported by your app users?

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[Eugene B]

Hi Scott,

This is not a device issue. Even if a device doesn’t have an SD card slot, AOSP supports USB hubs, which in turn support SD cards. AOSP also supports other external storage media.
In our Camera app, we give the user the option to choose which storage to use for saving media. We want the Camera app to behave reliably, regardless of whether the user understands the variety of SD cards and other external storage options.
If the storage turns out to be too slow, the app will stop recording video and notify the user that this storage does not support 4K recording.

[Scott Nien]

Thanks for the information. This makes sense. Let me double check,  so what CameraX can improve is to 

Avoid the OutOfMemory crash by 

1) adjust the internal buffer size properly 

2) provide a way to detect if the speed is fast enough for 4K recording, if not trigger an error to warn the app user. 

Is it correct?  

And do you think this SD cards / other USB storage case is very important for 4K recording as it needs large amount of disk space?  

[Eugene B]

Ideally, the CameraX API would automatically stop recording video if the accumulated buffer grows too quickly, for example with the too_slow_storage error—this would be a unified approach, as for other cases.

Regarding the second point, I don't see a quick way to determine the write speed of the selected storage. I developed a utility class for measuring speed and discovered the following:
Measurements revealed that when recording a file smaller than 25 megabytes, the measured write speed is significantly underestimated and does not reflect the actual speed.

For example, when recording a 10-20 MB file:
A low-class SD card shows a write speed of 2-3 MB/s.
A class 10 SD card shows 2.5-3.5 MB/s.
Internal storage shows 50-70 MB/s.

When recording a 25 MB file, the calculated speed is more realistic:
Low-class SD card: 2-3 MB/s.
Class 10 SD card: 5-8 MB/s.
Internal storage: 120-160 MB/s.

I don't think the Camera API should be responsible for determining the speed of the storage device itself.

Professional cameras supports 4K video recording to an SD card. I see no reason to limit the user. After all, we all strive to make our products better.

четверг, 4 декабря 2025 г. в 18:49:28 UTC+3, scot...@google.com: