| // Copyright 2017 The Fuchsia Authors. All rights reserved. |
| // Use of this source code is governed by a BSD-style license that can be |
| // found in the LICENSE file. |
| |
| #ifndef GARNET_BIN_MEDIA_AUDIO_SERVER_CONSTANTS_H_ |
| #define GARNET_BIN_MEDIA_AUDIO_SERVER_CONSTANTS_H_ |
| |
| #include <stdint.h> |
| |
| namespace media { |
| namespace audio { |
| |
| // The number of fractional bits used when expressing timestamps (in frame |
| // units) as fixed point integers. Ultimately, this determines the resolution |
| // that a source of PCM frames may be sampled at; there are 2^frac_bits |
| // positions between audio frames that the source stream may be sampled at. |
| // |
| // Using 64-bit signed timestamps means that we have 50 bits of whole frame |
| // units to work with. At 192KHz, this allows for ~186.3 years of usable range |
| // before rollover when starting from a frame counter of 0. |
| // |
| // With 13 bits of fractional position, a mix job's interpolation precision is |
| // only +/-61 ppm. Across multiple jobs we stay in sync, but for any single mix, |
| // this is our granularity. As an example, when resampling a 48 kHz audio |
| // packet, the "clicks on the dial" of our actual resampling rates are multiples |
| // of 6 Hz. Again, we do correct any positional error at mix job boundaries. |
| // |
| // This also affects our interpolation accuracy: because fractional position has |
| // a potential error of 2^-13, the worst-case error for interpolated values is |
| // [pos_err * max_intersample_delta]. This means full-scale very high-frequency |
| // signals are only guaranteed bit-for-bit accurate in the top 13 bits. |
| // TODO(mpuryear): MTWN-86 Consider even more fractional position precision. |
| constexpr uint32_t kPtsFractionalBits = 13; |
| constexpr uint32_t kPtsRoundingVal = 1 << (kPtsFractionalBits - 1); |
| // Used in places where PTS must be an integral number of frames. |
| constexpr uint32_t kPtsFractionalMask = (1 << kPtsFractionalBits) - 1; |
| |
| // This is the width of our floating-point audio processing pipeline. |
| constexpr uint32_t kAudioPipelineWidth = 25; |
| |
| // A compile time constant which is guaranteed to never be used as a valid |
| // generation ID (by any of the various things which use generation IDs to track |
| // changes to state). |
| constexpr uint32_t kInvalidGenerationId = 0; |
| |
| } // namespace audio |
| } // namespace media |
| |
| #endif // GARNET_BIN_MEDIA_AUDIO_SERVER_CONSTANTS_H_ |
