Derek Buitenhuis dwbuiten

Things to Look for When Evaluating Encoders

"Our encoder mixes DCT synergies and gamma radiation to provide excellent quality that abides by industry standard salsa dancing techniques, using adaptive streaming techniques." — Vendor.

First Steps

First, verify they actually have a product to sell that actually exists and can be tested in-house.

Warning signs: incredibly vague descriptions of the product, lots of "patent pending" claims with no real patents to be found, and insistence that they can do the testing for you and provide metrics instead of letting you test it yourself.

Problems & Solutions for Interaction Between C and Go

At Vimeo, on the transcoding team, we work a lot with Go, and a lot with C, for various tasks such as media ingest. This means we use CGO quite extensively, and consequently, have run into bits that are perhaps not very well documented, if at all. Below is my effort to document some of the problems we've run into, and how we fixed or worked around them.

Many of these are obviously wrong in retrospect, but hindsight is 20/20, and these problems do exist in many codebases currently.

Some are definitely ugly, and I much welcome better solutions! Tweet me at @daemon404 if you have any, or have your own CGO story/tips, please! I'd love to learn of them.

Table of Contents

	// This is pseudocode / example to explain what kind of implementation I mean.
	// I have not checked it for off-by-one errors, 100% accurate C compliance, etc.
	// It's just to show what I mean, implementation wise.

	#define SOME_DEFAULT_SIZE 20

	char vlc_uri_compose(const vlc_url_t uri)
	{
	char buf, enc;
	size_t len = SOME_DEFAULT_SIZE;

	draw.c:30: error: CHECKERS_DEAD_CODE
	Node not visited: 20
	28. static inline char get_char(char c)
	29. {
	30. > if (c > 31 && c < 127)
	31. return c;
	32. else
	33.

	Original code is here: https://github.com/dwbuiten/bxd/blob/master/draw.c#L28-34

	draw.c:30: error: CHECKERS_DEAD_CODE
	Node not visited: 20
	28. static inline char get_char(char c)
	29. {
	30. > if (c > 31 && c < 127)
	31. return c;
	32. else
	33.

	Original code here: https://github.com/dwbuiten/bxd/blob/master/draw.c#L28-34

	// Package cref implements a way to hose your Go garbage collection.
	package cref

	import (
	"fmt"
	"unsafe"
	)

	/*
	#include <pthread.h>

	#include <inttypes.h>
	#include <stdint.h>
	#include <stdio.h>
	#include <stdlib.h>
	#include <string.h>

	#include <lsmash.h>

	typedef struct ts {
	uint64_t dts;

	switch mystr {
	case "a", "b", "c", "d", "e":
	default:
	dostuff()
	}

	// versus

	if myster != "a" && mystr != "=" && mystr != "c" && mystr != "d" && mystr != "e" {
	dostuff()

	/*
	* posix_memalign wrapper with random failurres
	*
	* Copyright (c) 2013, Derek Buitenhuis
	*
	* Permission to use, copy, modify, and/or distribute this software for any
	* purpose with or without fee is hereby granted, provided that the above
	* copyright notice and this permission notice appear in all copies.
	*
	* THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES

	#!/usr/bin/env perl

	use strict;
	use warnings;
	use bigint;
	use File::Spec;
	use JSON::XS;

	my $filename = $ARGV[0];
	my $data = `ffprobe -show_streams -show_format -show_frames -of json $filename`;