MediaTranscoder - Compression is not applied when using MP4 encoding profile?

Question

MediaTranscoder - Compression is not applied when using MP4 encoding profile?

Jared Goodwin 21

I'm using MediaTranscoder to encode video from uncompressed ARGB frames. Example:

var sourceVideoProperties = VideoEncodingProperties.CreateUncompressed(
    MediaEncodingSubtypes.Argb32,
    evenWidth,
    evenHeight);

var videoDescriptor = new VideoStreamDescriptor(sourceVideoProperties);

var mediaStreamSource = new MediaStreamSource(videoDescriptor);

When using this as the MediaStreamSource for the transcoder, no compression is applied to the output video when using MP4 MediaEncodingProfile. Even if I diff the frames between each sample request to only write frames that have changed since the last, the resulting file is always the same size. In a 10-second recording, it didn't matter if I wrote 400 frames or 10 frames.

But if I use WMV profile, the file size is greatly reduced and fluctuates as you'd expect. More movement on screen results in larger file size.

Is this normal?

Thanks.

Xiaopo Yang - MSFT 12,731 Reputation points Microsoft External Staff

2021-11-22T06:39:49.797+00:00

Can the resulting file be played?, Is the media encoding profile created properly? and Hope the MediaTranscoding sample works for you.
Jared Goodwin 21 Reputation points

2021-11-22T16:03:45.937+00:00

Thank you for the reply!

Yes, the resulting file can be played, and the media encoding profile is created properly.

The sample you linked has the same problem. It will encode and create the MP4 file, but it doesn't apply any compression at all.

In the below image, I took a 10-second clip of my desktop with no changes occurring on the screen. The resulting video is 20MB (which is too large, and the reason I posted).

I used the sample project you linked to re-encode it. At 1080p, no file size change. Reducing the resolution changed the file size, but it's still huge for no changes happening.

Then I re-encoded using WMV at 1080p. Notice the file size is only 1.6 MB. It applied compression.

The 1.6 MB size is what you'd expect from 1080p MP4 as well. Since there are no changes happening on-screen, it should be roughly the same size as a screenshot. Each frame should only be a diff since the previous frame. If there are no changes, it should essentially be just one frame. But the MP4 profile appears to be encoding each frame in its entirety, without any diffing/compression.
Anonymous

2021-11-23T01:21:14.62+00:00

@Jared Goodwin Would you mind telling me what kind of project it is? Is it a UWP project or win32 project?
Jared Goodwin 21 Reputation points

2021-11-23T02:00:47.027+00:00

Both. But to avoid any suspicions that I'm doing something wrong, the behavior is present in this UWP project as well: https://github.com/MicrosoftDocs/SimpleRecorder/

A developer on the Windows Composition team has since added to it, and it still has the same issue: https://github.com/robmikh/SimpleRecorder

He also published it to the Windows Store: https://www.microsoft.com/en-us/p/simple-screen-recorder/9n5mvvbd0tgw

Try recording a window with no changes happening. The resulting MP4 is enormous.
Anonymous

2021-11-23T08:45:27.187+00:00

@Jared Goodwin I've confused about your issue. If I understand you correctly, you want to create videos that are compressed, right? But the API VideoEncodingProperties.CreateUncompressed you are calling is used for creating an uncompressed video. It is expected to get an uncompressed video if you are using this API.

I made a test in the SimpleRecorder app. First of all, I go to Project CaptureEncoder, find the Encoder class, change the MediaEncodingSubtypes.Bgra8 into MediaEncodingSubtypes.Argb32 as you posted. Then I created a .mp4 file and a .wmv file like you did. But both of these videos have similar sizes about 20-21MB. Based on the result I got, this API has the same behavior when creating MP4 and WMV files which is different from the result you got.
Jared Goodwin 21 Reputation points

2021-11-23T16:03:53.677+00:00

Shouldn't the source be irrelevant? Shouldn't an encoder be able to take an uncompressed source and encode/compress it? Isn't that the point?

And no, that is not the correct steps to reproduce this using the SimpleRecorder project. You'd need to change the output format in Encoder.cs. Not the source.

Anyhow, I made a sample project that shows you exactly what I'm talking about: https://github.com/lucent-sea/Mp4NoCompressionExample

Just run the application. You'll see the below.

Accepted answer

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Xiaopo Yang - MSFT 12,731 Reputation points Microsoft External Staff

2021-11-22T06:39:49.797+00:00

Can the resulting file be played?, Is the media encoding profile created properly? and Hope the MediaTranscoding sample works for you.
Jared Goodwin 21 Reputation points

2021-11-22T16:03:45.937+00:00

Thank you for the reply!

Yes, the resulting file can be played, and the media encoding profile is created properly.

The sample you linked has the same problem. It will encode and create the MP4 file, but it doesn't apply any compression at all.

In the below image, I took a 10-second clip of my desktop with no changes occurring on the screen. The resulting video is 20MB (which is too large, and the reason I posted).

I used the sample project you linked to re-encode it. At 1080p, no file size change. Reducing the resolution changed the file size, but it's still huge for no changes happening.

Then I re-encoded using WMV at 1080p. Notice the file size is only 1.6 MB. It applied compression.

The 1.6 MB size is what you'd expect from 1080p MP4 as well. Since there are no changes happening on-screen, it should be roughly the same size as a screenshot. Each frame should only be a diff since the previous frame. If there are no changes, it should essentially be just one frame. But the MP4 profile appears to be encoding each frame in its entirety, without any diffing/compression.
Anonymous

2021-11-23T01:21:14.62+00:00

@Jared Goodwin Would you mind telling me what kind of project it is? Is it a UWP project or win32 project?
Jared Goodwin 21 Reputation points

2021-11-23T02:00:47.027+00:00

Both. But to avoid any suspicions that I'm doing something wrong, the behavior is present in this UWP project as well: https://github.com/MicrosoftDocs/SimpleRecorder/

A developer on the Windows Composition team has since added to it, and it still has the same issue: https://github.com/robmikh/SimpleRecorder

He also published it to the Windows Store: https://www.microsoft.com/en-us/p/simple-screen-recorder/9n5mvvbd0tgw

Try recording a window with no changes happening. The resulting MP4 is enormous.
Anonymous

2021-11-23T08:45:27.187+00:00

@Jared Goodwin I've confused about your issue. If I understand you correctly, you want to create videos that are compressed, right? But the API VideoEncodingProperties.CreateUncompressed you are calling is used for creating an uncompressed video. It is expected to get an uncompressed video if you are using this API.

I made a test in the SimpleRecorder app. First of all, I go to Project CaptureEncoder, find the Encoder class, change the MediaEncodingSubtypes.Bgra8 into MediaEncodingSubtypes.Argb32 as you posted. Then I created a .mp4 file and a .wmv file like you did. But both of these videos have similar sizes about 20-21MB. Based on the result I got, this API has the same behavior when creating MP4 and WMV files which is different from the result you got.
Jared Goodwin 21 Reputation points

2021-11-23T16:03:53.677+00:00

Shouldn't the source be irrelevant? Shouldn't an encoder be able to take an uncompressed source and encode/compress it? Isn't that the point?

And no, that is not the correct steps to reproduce this using the SimpleRecorder project. You'd need to change the output format in Encoder.cs. Not the source.

Anyhow, I made a sample project that shows you exactly what I'm talking about: https://github.com/lucent-sea/Mp4NoCompressionExample

Just run the application. You'll see the below.

Answer 1

Anonymous

Hello,

Welcome to Microsoft Q&A!

@Jared Goodwin After talking to other engineers, we've found the reason for this behavior. When you are calling MediaEncodingProfile.CreateMp4 and MediaEncodingProfile.CreateWmv, the default compression format that used in these two methods is different. The default compression format for MP4 is H264 and the default compression format for WMV is WVC1. This is why the sizes are different between the MP4 file and the WMV file. If you set the encodingProfile.Video.Subtype = "H264" before creating a WMV file, you will get a WMV file which size is similar to the MP4 file. So this behavior is normal. You could check all the supported subtypes here: VideoEncodingProperties.Subtype Property

Thank you.

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Jared Goodwin 21 Reputation points

2021-12-03T19:29:17.177+00:00

Thank you very much for the information. I didn't realize the default compression formats had such a large difference in resulting file size. So it seems the problem is my ignorance on the topic. :)

Thanks for your patience and persistence. Take care!
Anonymous

2021-12-06T01:20:59.49+00:00

@Jared Goodwin There is a simple suggestion from the team, instead of changing the subtype when using the Auto quality setting when creating the VideoEncodingProfile, we do recommend specifying a specific profile, and then you can override the Bitrate property. This will work up to a point (sometimes the codec has minimal values for various frame sizes / color formats / framerates that it will use in place).

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MediaTranscoder - Compression is not applied when using MP4 encoding profile?

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