iOS HW encoder: Increase data rate limit
The iOS H264 video toolbox encoder is currently undershooting the
intended bitrate. This seems to be caused by the data rate limit
property. This CL increases the data rate limit to a set
percentage above the intended bitrate to avoid undershooting. The
AverageBitRate property is still set to the intended bitrate, which
keeps it from overshooting the intended bitrate.
BUG=b/28713684
Review-Url: https://codereview.webrtc.org/2177873003
Cr-Original-Commit-Position: refs/heads/master@{#13526}
Cr-Mirrored-From: https://chromium.googlesource.com/external/webrtc
Cr-Mirrored-Commit: 62d695f6550cb8577191f00af9df76c4d8474afc
diff --git a/modules/video_coding/codecs/h264/h264_video_toolbox_encoder.cc b/modules/video_coding/codecs/h264/h264_video_toolbox_encoder.cc
index bbf3f0f..4cbe2cd 100644
--- a/modules/video_coding/codecs/h264/h264_video_toolbox_encoder.cc
+++ b/modules/video_coding/codecs/h264/h264_video_toolbox_encoder.cc
@@ -28,6 +28,11 @@
namespace internal {
+// The ratio between kVTCompressionPropertyKey_DataRateLimits and
+// kVTCompressionPropertyKey_AverageBitRate. The data rate limit is set higher
+// than the average bit rate to avoid undershooting the target.
+const float kLimitToAverageBitRateFactor = 1.5f;
+
// Convenience function for creating a dictionary.
inline CFDictionaryRef CreateCFDictionary(CFTypeRef* keys,
CFTypeRef* values,
@@ -519,11 +524,12 @@
bitrate_bps);
// TODO(tkchin): Add a helper method to set array value.
- int64_t bytes_per_second_value = bitrate_bps / 8;
+ int64_t data_limit_bytes_per_second_value = static_cast<int64_t>(
+ bitrate_bps * internal::kLimitToAverageBitRateFactor / 8);
CFNumberRef bytes_per_second =
CFNumberCreate(kCFAllocatorDefault,
kCFNumberSInt64Type,
- &bytes_per_second_value);
+ &data_limit_bytes_per_second_value);
int64_t one_second_value = 1;
CFNumberRef one_second =
CFNumberCreate(kCFAllocatorDefault,
