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media: clarify MediaFormat.KEY_FRAME_RATE for video encoders

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Bug: 228530100
Change-Id: I4fb6d1228f9e84541e2048ac6dfe29d4f8939c02
This commit is contained in:
Lajos Molnar
2022-05-25 14:41:26 -07:00
parent c56fb0fdeb
commit 2e9d9128de
1 changed files with 15 additions and 5 deletions
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20
media/java/android/media/MediaFormat.java
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@@ -456,17 +456,27 @@ public final class MediaFormat {
/**
* A key describing the frame rate of a video format in frames/sec.
* <p>
* The associated value is normally an integer when the value is used by the platform,
* but video codecs also accept float configuration values.
* Specifically, {@link MediaExtractor#getTrackFormat MediaExtractor} provides an integer
* value corresponding to the frame rate information of the track if specified and non-zero.
* Otherwise, this key is not present. {@link MediaCodec#configure MediaCodec} accepts both
* float and integer values. This represents the desired operating frame rate if the
* float and integer values.
* <p>
* This represents the desired operating frame rate if the
* {@link #KEY_OPERATING_RATE} is not present and {@link #KEY_PRIORITY} is {@code 0}
* (realtime). For video encoders this value corresponds to the intended frame rate,
* although encoders are expected
* to support variable frame rate based on {@link MediaCodec.BufferInfo#presentationTimeUs
* buffer timestamp}. This key is not used in the {@code MediaCodec}
* (realtime). Otherwise, this is just informational.
* <p>
* For video encoders this value corresponds to the intended frame rate (the rate at which
* the application intends to send frames to the encoder, as calculated by the buffer
* timestamps, and not from the actual real-time rate that the frames are sent to
* the encoder). Encoders use this hint for rate control, specifically for the initial
* frames, as encoders are expected to support variable frame rate (for rate control) based
* on the actual {@link MediaCodec.BufferInfo#presentationTimeUs buffer timestamps} of
* subsequent frames.
* <p>
* This key is not used in the {@code MediaCodec}
* {@link MediaCodec#getInputFormat input}/{@link MediaCodec#getOutputFormat output} formats,
* nor by {@link MediaMuxer#addTrack MediaMuxer}.
*/