Extracted hardcoded constants from cast_rtp_stream.

chrome/renderer/media/cast_rtp_stream.cc

Index: chrome/renderer/media/cast_rtp_stream.cc
diff --git a/chrome/renderer/media/cast_rtp_stream.cc b/chrome/renderer/media/cast_rtp_stream.cc
index 1b9d2da7b055d32dfe99a87b7fd11399fa83e1c7..4716b2f1902477114599d543f1dd4d306eaa8092 100644
--- a/chrome/renderer/media/cast_rtp_stream.cc
+++ b/chrome/renderer/media/cast_rtp_stream.cc
@@ -181,7 +181,7 @@ bool ToAudioSenderConfig(const CastRtpParams& params,
   config->rtp_payload_type = params.payload.payload_type;
   config->use_external_encoder = false;
   config->frequency = params.payload.clock_rate;
-  if (config->frequency < 8000)
+  if (config->frequency < media::cast::kMinUnackedFrequency)

[miu, 2015/09/14 17:55:07]

8000 is the largest of the minimum sampling rate required by all codecs (e.g.,
Opus).  It has nothing to do with unacked frames.

[msu.koo, 2015/09/15 00:05:06]

Changed to use media::limits::kMinSampleRate instead.
And if the minimum audio sample rate is 8000 for all codecs,
I think we can also change the value of kMinSamleRate to 8000.(currently 3000)

[miu, 2015/09/15 04:16:57]

There's a difference: 3000 is an operational lower-bound for the entire audio
stack.  However, 8000 is the lower-bound for the audio codecs that process the
audio here.  So, this constant really does need to be 8000.

Can you add a kMinSampleRateForEncoding constant (set to 8000) here:
https://code.google.com/p/chromium/codesearch#chromium/src/media/cast/cast_de...

     return false;
   config->channels = params.payload.channels;
   if (config->channels < 1)
@@ -222,7 +222,7 @@ bool ToVideoSenderConfig(const CastRtpParams& params,
   config->start_bitrate = config->min_bitrate;
   config->max_frame_rate = static_cast<int>(
       std::max(1.0, params.payload.max_frame_rate) + 0.5);
-  if (config->max_frame_rate > 120)
+  if (config->max_frame_rate > media::cast::kMaxUnackedFrames)

[miu, 2015/09/14 17:55:07]

120 was chosen arbitrarily in the past.  Instead, I think
media::limits::kMaxFramesPerSecond is more appropriate.  You'll need to #include
"media/base/limits.h"

[msu.koo, 2015/09/15 00:05:06]

Done.

And IMHO, kMaxFramesPerSecond 1000 is too large for the MaxFPS. It was
originally introduced for video capture implementations, so I think 120 is also
OK for this value.

     return false;
   if (params.payload.codec_name == kCodecNameVp8) {
     config->use_external_encoder = IsHardwareVP8EncodingSupported();