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"Digital Signal Processing"
This post discusses how to record raw audio (PCM) and save it to wave file on Android. If you’re not familiar with WAVE audio file format, please refer to a previous post, WAVE Audio File Format.
The post is a follow up post for Record PCM Audio on Android. The [...]
This post discusses how to record PCM audio on Android with the android.media.AudioRecord class. If you’re not familiar with PCM, please read a previous post PCM Audio Format.
For the source code, please refer to AndroidPCMRecorder.
1. State Transition
The source code records the PCM audio with PcmAudioRecorder.java, which [...]
WAV (Waveform Audio File Format, also known as WAVE) is a commonly used audio file format for storing raw audio samples on Windows. It follows the RIFF (Resource Interchange File Format) generic format.
0. The Format
A wave file is a RIFF file with a “WAVE” chunk. The WAVE chunk consists of two [...]
Pulse Code Modulation (PCM) is a method to represent sampled analog signals in digital form, which is the standard form for digital audio representation in computers. In order to convert an analog signal to PCM, two steps are required. sampling: the magnitude of the analog signal are sampled regularly at uniform intervals. quantization: the value [...]
MPEG4 Part-2 introduced three error resilience tools, including Resynchronization, Data Partitioning and Reversible VLC. This post discusses Resynchronization only.
The Problem
The bitstream of a MPEG4 video frame (and lots of other video codecs) is encoded using VLC (Variable Length Coding). Because the number of bits for each coefficient varies and the length is [...]
There’re generally 3 ways to recover error caused by Internet transmission, including Retransmission, Redundant Data, and Error Concealment.
Retransmission
Retransmission is easy to understand. Just resend the packet that is lost or has error. It has the following pros and cons,
Pros:
Retransmission resends the entire packet, so the data error/lost is repaired accurately. [...]
This is the third method of the http video delivery. Unlike the first two methods: HTTP Progressive Download and Play, and HTTP Pseudo-streaming, this is a real streaming technology and it’s applicable for both live video and video on demand (VOD).
The basic idea of Dynamic Adaptive Streaming over HTTP (DASH) is [...]
HTTP Pseudo Streaming is the second method in HTTP Video Delivery. The method is also based on HTTP progressive download as the first method does, and it makes use of the partial download functionality of HTTP to allow user to seek the video to part that has not been downloaded yet.
HTTP Pseudo [...]
Progressive Download and Play is the first of the three methods in HTTP Video Delivery. The basic idea of this method is to embed the video through media player (e.g. JWPlayer, FlowPlayer etc.). When user request to play the video, a HTTP Get request will send to the web server, and the video will [...]
1. TCP Congestion Control and Window Size
TCP maintains a congestion window, which indicates the number of packets that TCP can send before an acknowledge for the first packet sent is received.
The congestion window size is default to 2 times of the maximum segment size (MSS, the largest amount of data in bytes [...]
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